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Audio Note DAC 5 vs AMR DP-777

پنجشنبه 4 آگوست 2016
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دیشب بین دک 33000 دلاری Audio Note UK و دک 5000 دلاری AMR تست گرفتیم که AMR خیلی بهتر صدا میداد. من توضیحات رو مینویسم و هنوز ذهنم نمیتونه باور کنه این اختلاف رو و بازم آخر ذهنم اینه نکنه DAC آئودیونت باید سرویس میشده یا لامپهاش عوض میشده و یا یه مشکلی بوده. در هر صورت تست دیشب خونه آرمن انجام شد و آرمن گفت شرایط تست برای هر دو مساوی هست و فقط کابل برق این دو تا با هم فرق داره. اینو بگم DAC باید برای تست خوب کار کنه و گرم بشه ، آرمن میگفت رومی هیچوقت DAC هاشو خاموش نمیکنه.

این تست هم Blind انجام شد و هم بعدش جدا DAC هارو شنیدیم. AMR خیلی تو میدرنج بهتر بود انگار صدا تو میدرنج یه Harmonic Integrity خیلی خوبی داشت و شفاف تر هم بود اما Audio Note کلا قاطی بود صداش و حالت Coherent و پایدار نداشت.

من اولش که Blind تست گرفتیم و نمیدونستم کدوم DAC داره پخش میکنه صدا رو ، گفتم انگار این DAC (منظورم Audio Note هست) تازه به برق وصل شده و صداش هنوز پایدار نشده و از نظر داینامیکی و تونالیته قاطی داره اما آرمن گفت هر دو DAC ها به یک اندازه کار کردند و روشن بودند.

در هر صورت یه راه برای اینکه بفهمیم وضعیت Audio Note چطوره داریم اونم اینکه DAC EAR 4 من رسید با AMR مقایسه اش بکنیم و اگر AMR با همین اختلاف EAR رو بزنه که معلوم میشه AMR سلطان DAC هاست و Audio Note سالم بوده اما اگر EAR DAC 4 صداش به AMR نزدیک باشه این احتمال شکل میگیره که Audio Note نیاز به سرویس داشته باشه.

در هر صورت Audio Note خیلی ناامید کننده بود. من قبلا اگر یادتون باشه نوشتم DAC Audio Note بهترین DAC تو میکرو هست :

DAC پیشنهادی

حالا منتظر میمانیم ببینیم EAR 4 وضعیت رو چطور شکل میده. حداقل چیزی که از Audio Note انتظار میرفت میدرنج خوب بود که اونم اصلا خوب نبود.

ولی حالا این تست حداقل این نتیجه رو داشته که فاکتور قیمت رو باید از ذهنمون دور کنیم و چون یک DAC قیمتش 50000 دلاره پس باید صدای خیلی بهتری از DAC مثلا 5000 دلاری بده اینطور نیست و باید تو شرایط یکسان صداهارو شنید.

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Berkeley Alpha USB to S/PDIF Converter

دوشنبه 1 آگوست 2016
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اینم داره به جمع سیستم من اضافه میشه ، دلیلش اینه EAR DAC 4 ورودی USB رو به خوبی SPDIF پخش نمیکنه و با پیشنهاد خود Gordon که ایشون تو طراحی همین Alpha USB نقش داشت تصمیم گرفتم این USB to SPDIF Converter رو بیارم . ست نهایی این میشه :

Macbook pro 2014 USB 3.0 -> Berkeley Alpha USB -> EAR DAC 4 (BNC input) -> EAR HP4 Headphone Amplifier (XLR input) -> Sennheiser HD800

All Cabling : Purist audio

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Philips TDA1541 Multi-bit DAC R-2R 1984 1985

یکشنبه 31 جولای 2016
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ظاهرا TDA1541 اگر درست پیاده سازی بشه سلطان DAC های دنیاست. بعد از این DAC میشه روی کیفیت Wolfson WM8741 و AD1865 حساب کرد. تورستن طراح AMR خیلی روی این DAC کار کرده.

این DAC EAR ما از گمرک ترخیص بشه یه تست عالی بین EAR DAC 4 و Audio Note DAC 5 و AMR DP-777 میگیریم. اولی از Wolfson WM8741 استفاده میکنه ، دومی از AD1865 و سومی از TDA1543 که این تست خیلی جالب خواهد شد. اولی 8000 دلار هست دومی 33000 دلار و سومی 5000 دلار.

در مورد مبدل مالتی بیت TDA1541 فیلیپس که در AMR CD-77 استفاده شده بخونید :

http://www.dutchaudioclassics.nl/philips-tda1541.asp

Philips TDA1541 FAQ

What is a TDA1541 DAC?
The TDA1541 series are multi-bit DACs employing a DEM (dynamic ekement matching) circuit.
What is DEM?
To put it simply, DEM (patented by R. van der Plassche) is a superior system developed by Philips technicians that employes 4 to 5 current sources inside the DAC applied in turn to achieve a 1/4 to 1/5 reduction in DAC conversion errors. At first, the TDA1541 was used in combination with the Philips-made SAA7220P/A 4x over sampling digital filter (a noise shaper circuit was not required and was not used).
When and where was the TDA1541 produced?
The TDA1541 (non -A) was launched from 1985 to 1988, and it had no grades. The TDA1541 was specified for exceptional 1/2 LSB linearity. The TDA1541A was produced from 1988 to 1998.
The silicon wafer of the TDA1541 were produced at Philips Nijmegen. Final assembly was at plants in Holland, Taiwan, China or India.
What grades does the TDA1541A have?
The TDA1541A has 4 grades: standard, The R1, the S1 single crown and the S2 double (or gold) crown.
What does the grades mean?
The (standard) TDA1541A is specified at THD+N of 0.8% (-42 dB). The TDA1541A S1 and TDA1541A S2 grades are specified at THD+N of 0.45% (-47 dB) at -60 dBFS. In addition, S2 is specified for THD+N of 0.0014 % (-97 dB) at full level, as opposed to 0.0018% claimed for non S2 grade. The S versions are guaranteed by Philips for this performance, but that does not mean that non S grades can not match the same performance level. Apart from S grades there is also R1 grade. However Philips documentation is a little confusing about it – sometimes it is slightly better specified than unmarked TDA1541A, sometimes it is inferior.

There will still be intrinsic errors in DAC linearity due to the tolerance in the alignments of the various masks during the IC production process. As further fine-tuning of the DACs is not possible, Philips has adopted a grading process to pick out those which offer the best performance. When the finished doped and etched silicon wafer emerges from the semi-conductor plant, it carries many dozens of individual DACs. A computer-controlled tester, consisting of 28 needle probes, then connects to the appropiate pads on each raw DAC die, providing power and supplying serial data from a CD player. If a DAC fails to work in this go/no-go test, the result being no analog music output, it is marked with a paint spot. Automatic machinery then slices the wafer into the individual dies and mounts those that passed the initial test in the familiar 28-pin DIL plastic package.

At this stage, the finished TDA1541 ICs are graded by a computer-controlled test station into three classes.

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Peter Qvortrup On Digital

یکشنبه 31 جولای 2016
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Audio Note DAC 5 Special Review

Peter Qvortrup On Digital

Jack: Peter, please share with us your opinion on the basic differences between CD and vinyl sound.

Peter: My view is that digital cannot resemble the original because of the inaccuracies introduced at the point of entry in the digital domain. The errors and omissions introduced by all current and past methods of conversion are so great that, at best, all we get is a card board copy of the original and it is clearly audible, as a quick comparison between a decent turntable and even the most expensive CD replay set up will quickly reveal.

This is because much like the flawed assumptions used by mathematicians to create the financial “innovations” which lie at the heart of the current financial crisis, the fundamental assumptions that created the way we digitize the analogue signal also fail to describe the content of dynamic wide band signals and the way they flow. The end result is a set of mathematical formulas that are sadly lacking in their ability to model the full range of variables in a music signal, and as a result when we come to make the analogue to digital conversion process, the bar is set at a level which is lower than it needs to be, resulting in conversion technology which does not do justice to the analogue signal it is being presented with, resulting in an anemic digital version of the analogue original.

It is therefore no major surprise that the digital medium, as we know it, lacks authority, authenticity, immediacy, instrumental medium and density, dimensionality, and overall presence when compared to its analogue version, to the point where even some digital recordings sound better on LP than the CD (the reverse is of course also occasionally true, but for sake of a proper comparison, we should always compare early all-analogue recordings on LP with their CD counterparts from the early to mid 1980s, my experience has always been that AAD recordings generally sound better than ADD, and ADD generally sounds better than DDD), which leads me to believe that the signal damage goes beyond merely the digital conversion process itself, as it would appear that the longer the signal stays in the digital domain the more damage it suffers, which may also explain some aspect of what I hear in music servers.

The high “resolution” formats like SACD and DVD-A are no better, just different versions of the same problems that beset Redbook, but unlike standard Redbook, the SACD/DVD-A converters are virtually impossible to improve upon as the 1Bit system they use do not allow removing the oversampling and digital filtering, for example, so we are reduced to playing with component choices and power supply configurations, which is like putting lipstick on a bulldog, to use a currently popular phrase!

Jack: Then Peter, how did you come to build some of the most musical sounding CD players, DACs, and Transports?

Peter: Well, from the onset I disliked CD with a vengeance, but over some years I was increasingly faced with the opposing choices or dilemma if you like, of preferring the quality of the purely analogue source but also a great need to be able to hear a lot of the music I liked that only came out on CD. So, I had no real choice but to try to work out how one makes a digital-analogue converter that does not completely sucks the life out of any musician’s best efforts, including when the recording engineers have also not done their greatest job, which of course many LPs also suffer under, but which to me at least manifests itself as far worse when it is on CD than LP.

I always felt that the main improvements were available in the DAC, so that is where our main efforts have been concentrated. However, recent development work has shown that the CD transport has equally great potential for improvement, so considerable efforts are now given to find out how far the CD transport can be taken: We now employ a valve power supply in our best CD transport for part of the circuit!

Perhaps a little history?

In 1991, I set about with my engineer at the time, Guy Adams (of Voyd Turntables fame!) to develop a digital-to-analogue converter which has a less digital signature. This work led to the use of a transformer as the I/V interface, a practice we patented across the world, and the DAC3 was born in 1993. I have always been doubtful about techniques that purport to improve the signal, so sometime in 1994 I asked Guy whether it was possible to remove the oversampling and digital filters from the converter. Guy felt it was not feasible after speaking to various people at Burr Brown, so in late 1995 I mentioned it to Andy Grove, and Andy said he would look at it, a prototype was made a week later and the sound was a revelation, although it needed some fine tuning to get rid of the out of band interference.

We released the first non-oversampling (we call it 1xoversampling) design as the DAC5 Special in July 1997, and the rest is really history. We have spent the years since then refining the circuit, I/V interfaces and power supplies.

We added dedicated 1xoversampled CD players in 1998 and started work on CD transports in 1997, the first one being the CDT Two, unfortunately the Korean manufacturers who were building all the CD products for us went under in 2000, and it took us another 4 – 5 years to develop a replacement for the CDT Two. The CDT Two/II was released in late 2004.

Jack: One last question Peter, what are Audio Note’s future plans for digital playback?

Peter: We continue to refine the circuitry and power supplies and we keep discovering incremental improvements to add to the circuits, components and materials. As an ultimate statement, Andy has been working on two major projects, the first is an all discrete 20 – 24 bit converter, and the second, which is more interesting, is a completely new conversion system which we originally designed as an out-of-house project for a company that does investigations into molecular resonance in materials; initial experiments look promising, so we shall see.

On the CD transport side, we are finishing development of the CDT Five, where a couple of valve in part of the power supply has shown that even here, valves are superior to semiconductors.

I think that covers it!

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PCM vs Delta Sigma & DSD

جمعه 29 جولای 2016
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این دو روزه خیلی با Gordon ایمیل بازی کردم. یکی از بهترین طراحان USB DAC و کلی هم راهنماییم کرد. ایشون برای خیلی از شرکت ها DAC طراحی کرده و فقط روی برند خودش فعالیت تجاری نداره. جسیکا دزل که از کاربران خیلی فعال و باهوش کلاب رومی هست از DAC این طراح استفاده میکنه و خود رومی هم نوشته شنیدم اگر کسی بتونه USB رو خوب پیاده سازی کنه نتیجه خیلی عالی هست و خود Gordon هم معتقده اگر USB DAC خوب پیاده سازی بشه خیلی بهتر از SPDIF هست. کلا از SPDIF دوری میکنه.

آقای Gordon به من گفت با مک بوک پرو خودت حتما هارد اکسترنال هم بگیر که با پورت Thunderbolt کار کنه. توصیه کرد حتما از کابل خوب استفاده کنم و خودش از Audio Quest استفاده میکنه. گفته ممکنه کابل خیلی گران هم بخرید اما اون کابل USB یا SPDIF خوب نباشه. گفت از Audirvana بدون دخالت iTunes استفاده کنم. گفت پورت سمت راست مک بوک بهتره برای گرفتن سیگنال USB و برای ریپ کردن سی دی حتما error correction برنامه itunes باید فعال باشه. گفت بین فرمت های ALAC , WAVE و FLAC و … از فرمت AIFF برای مک استفاده کنم. من قبلا خونده بودم WAVE بهتره اما گوردون گفت از AIFF استفاده کنم.

آخرش هم گفت :

Amir,

Learn by doing, not by reading.

این جمله معنی زیادی داره.

اما در مورد تبدیل آنالوگ به دیجیتال :

ببینید دیتای دیجیتال یک سری 0 و 1 هست که ما تعیین میکنیم به چه شکل اون سیگنال آنالوگ به این 0 و 1 ها تبدیل بشه . دو فرمت رایج فعلی PCM و DSD هست. تو حالت PCM ما با Analog to Digital Converter میاییم با یه فرکانسی مثلا 44.1Khz اندازه ولتاژ سیگنال آنالوگ رو میخونیم و اون عدد رو به یه عدد دیجیتال تبدیل میکنیم. عدد دیجیتال محدود و قابل شمارش هست مثلا اگر 2 بیت باشه ما 4 تا عدد داریم و اگر 3 بیت باشه ما 8 حالت داریم و اگر 16 بیت باشه ما مقادیر 0 تا 65536 رو خواهیم داشت. هر بیت فقط دو حالت 0 و 1 رو میتونه داشته باشه و با n تعداد بیت ما 2 به توان n حالت داریم .

حالا برای 16 بیت ما میتونیم 65536 حالت داشته باشیم. کاری که میکنیم اینه محدوده ولتاژ آنالوگ رو که مثلا بین -2 تا +2 ولت هست رو به 65536 قیمت تقسیم میکنیم و تو تبدیل آنالوگ به دیجیتال اندازه ولتاژ به یکی از این 65536 عدد نزدیکتره و اون عدد رو براش اختصاص میدیم. مثلا ولتاژ 0 ولت میفته روی  32768 و سیستم اینجوریه که ما با فرکانس 44.1khz کلاک میزنیم و با هر کلاک 16 بیت اطلاعات رو از روی شکل موج آنالوک تبدیل به دیجیتال میکنیم. شکل زیر 3 بیت رو نشون داده.

به عبارتی معنی PCM 16-bit 44.1khz این میشه ما هر 1 تقسیم بر 44100 ام ثانیه (میشه هر 0.000022675737 ام ثانیه) 16 بیت دیتا دیجیتال استخراج میکنیم.

برای PCM 24-bit 192khz هم همین منطق هست و فقط با فرکانس بیشتری ما 24 بیت دیتا ذخیره میکنیم. عبارت PCM مخفف Pulse Code Modulation  هست.

اما در مورد DSD این طور نیست و ما با فرکانس 2.8 مگا هرتز فقط 1 بیت ذخیره میکنیم. ببینید :

تو شکل بالا ما فقط یک بیت داریم که یا 0 هست یا 1 و با فرکانس بالا 2.8 مگا هرتز سیگنال آنالوگ رو رصد میکنه و وقتی شیب تغییرات سیگنال آنالوگ زیادتره مثل نقطه شروع شکل بالا این بیت بین 0 و 1 بیشتر نوسان میکنه و هر چقدر که به قله شکل موج سینوسی نزدیک میشیم و روند تغییر دامنه ولتاژ آهسته تر میشه میبینید اون بیت دیرتر تغییر وضعیت میده و یه جورایی فرکانس تغییر اون بیت بر اساس مشتق تابع سیگنال آنالوگ هست.

همونطور که میبینید سیستم  DSD پیچیده تر از PCM بنظر میاد. به این نوع تبدیل کردن میگیم Pulse Density Modulation یا همان PDM .

Pulse-density modulation, or PDM, is a form of modulation used to represent an analog signal with a binary signal. In a PDM signal, specific amplitude values are not encoded into codewords of pulses of different weight as they would be in pulse-code modulation (PCM). Instead, it is the relative density of the pulses that corresponds to the analog signal’s amplitude. The output of a 1-bit DAC is the same as the PDM encoding of the signal. Pulse-width modulation (PWM) is a special case of PDM where the switching frequency is fixed and all the pulses corresponding to one sample are contiguous in the digital signal. For a 50% voltage with a resolution of 8-bits, a PWM waveform will turn on for 128 clock cycles and then off for the remaining 128 cycles. With PDM and the same clock rate the signal would alternate between on and off every other cycle. The average is 50% for both waveforms, but the PDM signal switches more often. For 100% or 0% level, they are the same.

تو حالت PDM میبینید که بر اساس تغییرات ما یک بیت رو تغییر میدیم و همانطور که میدانید تو آمپلی فایر های Class D هم داره چنین اتفاقی میفته و ما با تبدیل تغییرات سیگنال آنالوگ به 1 بیت اونو کد میکنیم. یعنی منطق آمپلی فایر Class D و منطق DSD و منطق Delta Sigma همگی به این برمیگردند که ما یک بیت داریم با یک فرکانس بالا و اون بیت بر اساس سرعت تغییرات فرکانسش تغییر میکنه.

حالا میریم سراغ قسمت تبدیل دیحیتال به آنالوگ.

تو قسمت اول که آنالوگ تبدیل به دیجیتال شد ما برای PCM از مالتی بیت استفاده کردیم و برای DSD از سینگل بیت و حالا راه درستش اینه که برای بازگشت از دیجیتال به آنالوگ برای PCM از DAC مالتی بیت استفاده کنیم و برای DSD از DAC سینگل بیت .

سیستم مالتی بیت واقعی همین سیستم R-2R Ladder هست که ولتاژ هر بیت به یک مقاومت پسیو وصل میشه و تو خروجی از جمع ولتاژها سیگنال آنالوگ کاملا خطی ساخته میشه. به این حالت میگن True Multi-bit یا همان R-2R Conversion .

اینم شکل دیگر :

این حالت عالیه و رومی و تورستن هم به گفته آرمن موافق همین سیستم True Multi-bit هست. مقاله MSB و Lampizator رو بخونید جالبه :

http://www.mother-of-tone.com/conversion.htm

http://www.msbtech.com/support/dac4_vince.php?Page=supportHome

http://www.msbtech.com/support/How_DACs_Work.php?Page=supportHome

http://www.lampizator.eu/Fikus/R2R_DISCRETE.html

نکته اینه قدیما از مقاومت استفاده میشد بعدش Analog Device و Philips و Burr Brown اومدند و همین سیستم r2-r رو داخل یک چیپ پیاده سازی کردند.

The TDA chip is nothing but a ladder of several hundred resistors built in the form of integrated circuit (silicon chip) and hence miniaturized to a reasonable size, usable in home electronics. This type of DAC chips is called multibit or R2R. (resistor to resistor)

اون analog Device اومد AD1865 رو زد و Philips مدل TDA1541 رو زد و Burr Brown هم مدل PCM1704 رو زد. بعدش دیگه کلا بساط R2R برچیده شد .

The absolute peak of R2R was the chip from Burr Brown (Japan) (later acquired by Texas) called PCM1704, with close followers of Philips’ TDA1541A, (and 1547) Analog Devices AD1865 and the Burr Brown’s own PCM 63. These chips are considered the pinnacle of the PCM era and were all discontinued about 20 years ago.

این DAC ها همشون برای 44.1khz و 16 بیت بودند و برای فرکانس های بالاتر و بیت بیشتر ورژنی ندادند. البته فک کنم PCM1704 تا 96 کیلوهرتز هم میره با 24 بیت. خود Lavry برای DAC 2002 مجبور شد از همون مقاومت ها استفاده کنه برای فرکانسهای بالاتر و 24 بیت.

از AD1865 شرکت Audio Note استفاده میکنه ، از TDA1541 شرکت AMR و Zanden استفاده میکنند ، از PCM1704 هم چند شرکت محدود دیگه. شکل زیر شبکه مقاومت هارو ببینید :

لیست DAC های مالتی بیت :

CEC DA 0 3.0
Trinity DAC
Ypsilon DAC 100
Phasure NOS1 DAC
MSB Platinum
Total DAC
Audial DAC Model S (Pedja Rogic)
AMR top DAC and CD-77 (Thorsten Loesch)
Lampizator
Wavelength USB DAC
Exasound
Reimyo
CH precision

Acoustic Plan

Zanden Audio
Audio Zone DAC-1

Audio Note UK

ادامه دارد …

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Wavelength Audio Wavelink HS 24/192

پنجشنبه 28 جولای 2016
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این DAC 4 شرکت EAR احتمالا نیاز به یه رابط SPDIF داره. من بین همه این رابط ها از WaveLink HS خوشم اومده که در زیر میبینید :

 

Wavelength Audio – WaveLink HS 24/192 USB to SPDIF converter $900

  • Streamlength Asynchronous USB
  • XMOS USB receiver
  • Sampling Frequency : 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4khZ, 192kHz
  • Bit depth: 16/24
  • Output: S/PDIF (BNC)
    Included is BNC-BNC SPDIF cable and with a mating BNC->RCA adapter
  • Thesycon USB Class 2 Audio driver (Windows)
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در ادامه DAC و Computer Audio

چهار شنبه 27 جولای 2016
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اول این لینک هارو دقیق بخونید خیلی خوبن :

http://www.stereophile.com/content/pdm-pwm-delta-sigma-1-bit-dacs#uvK84ec8zX22B853.97
http://www.thewelltemperedcomputer.com/index.html
http://www.mojo-audio.com/blog/

Thorsten Loesch
http://www.audiostream.com/content/qa-thorsten-loesch-amrifi#lj9GAqmbHhKALb2T.97

Gordon Rankin
http://www.audiostream.com/content/qa-wavelength-audios-gordon-rankin#H5fQlcaW35sB3Gl2.97

http://www.6moons.com/audioreviews/wavelength2/brick_2.html

John Swenson
http://www.audiostream.com/content/qa-john-swenson-part-1-what-digital#mh5Q2RTVxyOBCJRK.97
http://www.audiostream.com/content/qa-john-swenson-part-2-are-bits-just-bits
http://www.audiostream.com/content/qa-john-swenson-part-3-how-bit-perfect-software-can-affect-sound

Steve Nugent
http://www.audiostream.com/content/qa-steve-nugent-empirical-audio

Benjamin Zwickel
http://www.mojo-audio.com/blog/computer-audio-misconceptions/

Pedja Rogic
https://www.audialonline.com/topics/

http://www.monoandstereo.com/2008/04/interview-with-pedja-rogic-of-audial.html

این روزها در مورد DAC و موضوع حذف نویز و جیتر از PC میخونم. تورستن و گوردون و ژان و استو بیشترین تحقیقات رو تو زمینه گرفتن بهترین نتیجه از PC داشتند با ارتباط USB . دو مورد هست یک ایزوله کردن (Galvanic USB Isolation) گالوانیک نویز PC از DAC که هر چقدر ایزوله تر باشه بهتره اما با امکانات این صنعت (دو راه یکی کوپل نوری که جیتر بیشتری داره و دیگری استفاده از چیپ های Analog Device مثل ADUM4160 که هم محدودیت 96کیلوهرتز دارند و هم جیتر بیشتر) عملا هر چقدر ایزولیشن بیشتر بشه جیتر هم بیشتر میشه و موضوع مهم دیگر برای صدای خوب حذف و کاهش جیتر که اونم کار راحتی نیست.

First isolation is a good thing to have. I run a CG filter from my main power and put all the computer stuff on one side and all the analog on another. That way the switching computer noise has 2 filters to jump thru before it gets to the analog side.

I isolate at the I2S level. We found over the years that this was the best place for it. We reclock all the signals on the DAC side so the jitter is very low.

Using the Analog Devices ADUM series… well requires some engineering. First it is not setup to drive cables. These chips were meant to be on the board of the isolating endpoint. They also don’t sound that good… not sure why… maybe the same reason some USB cables don’t sound good. They are limited in speed to Full Speed or 24/96.

Most of the current asynchronous or even adaptive have no isolation. Anything that is self powered cannot have isolation…. well SPDIF converters can because they can have a transformer or optical output. But then again as pointed out above SPDIF leads to more jitter. This does not mean they are bad. These just may require a little more setup and adjustments than those that are.

I really would not get hung up on this as much as getting something that sounds good to you. Visit a dealer or have a dealer send you something to hear. Don’t buy by numbers or what people say here. Nobody listens the same or has the same system, room etc…

have fun!
Gordon

فعلا با نتایج من تو اینترنت بهترین حالت Computer Audio گرفتن دیتا از asynchronous usb کامپیوتر هست.

DAC بهتره و شاید لازمه که True Multi-Bit باشه یعنی از سیستم R-2R استفاده کنه و نه از سیستم Delta Sigma و حتی اگر عبارت Multi-Bit رو قبل Delta Sigma دیدید بدونید اون دک مالتی بیت واقعی نیست.

http://www.hifi.ir/wp-content/uploads/2016/07/Best-Performance.pdf

http://www.mojo-audio.com/blog/optimizing-os-x-yosemite/

Introduction:

So you have an Apple computer running OS X Yosemite and you want to optimize performance. I’ve got you covered. If you prefer to run an older version of OS X, I have another optimization blog that covers Snow Leopard through Mountain Lion.

Less is more…

It’s obvious Steve Jobs is dead. Forget about the fact that when Yosemite was first released it had so many bugs and conflicts you would think it was engineered by Microsoft. Apple was on the cutting edge of professional audio and video production, photography, and CAD, but has now redirected their marketing efforts toward the average social networking, iCloud using, multiple mobile device consumer.

Yosemite emphasizes a plethora of “eye candy” aesthetic features, automated multi-device and multi-platform integration, and organizational apps such as Mission Control, Dashboard, and Widgets.

The more of these optional processes you remove, the more you’ll improve Yosemite’s performance.

My company, Mojo Audio, manufactures and sells high-end computerized music and video servers for the home theater enthusiast and recording/editing professional. Though this blog was written to assist our customers in optimizing the performance of Yosemite running on their upgraded Mac Mini media servers, these same optimizations will work on any Mac running Yosemite.

I’ll walk you through exactly what you need to do to disable memory resident programs that automatically load by default when Yosemite boots up. And I’ll also show you how to turn off optional wireless control interfaces, such as infrared, WiFi, and Bluetooth.

When you disable these optional processes and reallocate system resources, your computer does less switching, swapping, interrupting, and error correcting. Freeing up system resources and turning off unused wireless control interfaces results in noticeably more efficient performance which translates to a more fluid and coherent audio and video presentation.

Warning! I recommend that before making any changes or updating software in any computer that you backup your drives. Using “cloning” software, such as Carbon Copy Cloner, creates a bootable backup.

It’s a perfect use of your time . . . you can clone your drives while you review the rest of this guide.


Start with a clean install of Yosemite:

It’s often easier to start with a clean slate than to figure out how to turn off and undo things we may have unknowingly turned on.

You did remember to back up your data and boot drives, right?

When you do a clean install you’re going to erase everything, so now’s a good time to make and test (yes, test) your system backups.

Warning! When doing a clean install do not activate any automated features. Activate only one web browser, preferably Safari. Don’t activate any optional features or plug-ins, such as Google Chrome. BTW, Chrome and Yosemite don’t play nice together, so I wouldn’t recommend using Chrome under any circumstances.

Here is a link to a guide on how to do a clean install.

Now that you’re back to clean, and nothing optional has been added, I’ll show you how to turn off a series of default resident processes that automatically boot up with Yosemite.


Improve Safari performance:

Safari does all sorts of things automatically to enhance your browsing experience. Of course, anything automatic consumes system resources. One option would be installing software, such as ClicktoPlugin, that prevents Safari from automatically loading plugs-ins.

Software like ClicktoPlugin not only speeds up browsing, but also reduces fan speed and extends battery life. It also improves performance of audio and video streaming.

The way it works is that it replaces any plug-in object with an unobtrusive placeholder that can be clicked on to load the embedded content of the plug-in. Now plug-ins only activate manually.

Another option you have instead of or in addition to using a plug-in management Application would be to uninstall Adobe Flash. Without Flash and plug-ins, Safari performs better.


Clear your desktop:

Remove any files, folders, or infrequently used Dock icons. These convenience and organizational options slow down performance by requiring the system to constantly redraw them on the screen.

Remove from Dock

For a minimized Dock, the only icons you need are Finder and Trash. The rest of the icons can be deleted. Some people like to keep Launchpad in their Dock for easier access to Applications.

Launchpad

To keep icons in your Dock, opposite click on the icon and select Keep in Dock. If you use an Application all the time and want it to open whenever you restart your computer, just opposite click on the icon and select Open at Login.

Other Keep 2

If you are optimizing for audio or video, you want your player and/or recording software to automatically open at Login. For desktop use, this could be accounting software, CAD software, and/or a web browser.

Applications automatically opening when the computer restarts is very important to restore function for media servers or home automation.

Close all Applications

Before applying any optimizations, make certain the only application running is Finder.

The Force Quit window will allow you to view all applications that are running.

Go into the  Apple Menu, drop-down menu, and select Force Quit.

Click to Enlarge

Click on and highlight an application. Press the Force Quit button in the lower right corner. Repeat until the only application shown is Finder.

Click to Enlarge


Disable pretty and automatic:

Disabling “eye candy” such as Transparency and turning off automated features such as Widgets will improve Yosemite performance.

Reduce Transparency:

Go into the  Apple Menu, select System Preferences, and click on Accessibility.

Yosemite System Preferences

In the Accessibility window, check the Reduce Transparency box.

Reduce Transparency

Change Minimize Windows to Scale:

Any effect that is used when minimizing windows unnecessarily consumes system resources.

Go into the  Apple Menu, select System Preferences, and click on Dock. Change the Minimize windows from Genie effect to Scale effect.

Dock

Uncheck the Animate opening applications box. You can check or uncheck any of these features. Remember: less is more.

Disable Widgets:

Widgets are cool looking and convenient, but they use quite a bit of system resources. Not updating Widgets significantly speeds up rebooting and improves performance. Click on the Widgets toggle in the upper right corner.

Widgets 2

Uncheck, deactivate, and remove as many items as possible from both the Today and the Notifications panels.

Disable the Extensions that you don’t need:

Go into the  Apple Menu, select System Preferences, and click on Extension.

Extensions

Go to the Today options in the left column and uncheck any or all extensions you don’t require.

Disable sleep, Power Nap, and screen saver:

Go into the  Apple Menu, select System Preferences, and click on Energy Saver.

Energy Saver

Uncheck everything except Prevent computer from sleeping automatically and Start up automatically after a power failure. Move the Turn display off after slider to the far left set to Never.

Disable Notifications:

Go into the  Apple Menu, select System Preferences, and click on Notifications.

Notifications

In the left column click on and highlight the Do not disturb option and uncheck as many boxes as possible.

Notifications 2

In the left column click on and highlight each of the features (Calendar, Face Time, Mail, Messages, etc) and uncheck as many boxes as possible. Change to 1 recent item for each feature.

Speed up new Finder window generation:

In the Finder pull down menu select Preferences.

Finder Preferences 2

Set the New Finder windows show to the place you go to most often. This could be Desktop, Documents, Music or your user home folder.

Finder Preferences

You can also control several other aesthetic features by checking or unchecking these features.

Removing unused languages:

Go into the  Apple Menu, select System Preferences, and click on Languages & Region.

Language

Make certain that only the language(s) you use are listed. Highlight and delete unused languages and add any languages you may need using the + and – buttons.

Removing the presentation order for Spotlight:

Go into the  Apple Menu, select System Preferences, and click on Spotlight.

Spotlight 2

In the Spotlight control window, select the Search Results tab.

Spotlight

You’ll see a list of Applications with check boxes next to them. Uncheck all of the boxes. There is no point in leaving “Music” for a music or media server because your library/player software doesn’t access through Spotlight.

Disabling Login Items:

Ideally you want only one Application to automatically open when you login to your computer. If you use your Mac as a dedicated music server, you would want only your player software to open at Login. If you are a professional, you would want your accounting software, CAD software, etc. to automatically open at Login. At the same time, you want to disable any other applications that may automatically want to open at Login.

Go into the  Apple Menu, select System Preferences, and click on Users & Groups. To streamline the Login items click on the Login Items tab at the top.

Users & Groups 3

Note: This is the same window you can add guests and users with restricted access. For example, you could allow your children to log on to your media server and play recordings from your NAS drive, but not have access to change any of your administrative settings.

You’ll see all the Applications you’ve set to automatically open at Login in the main window. You can remove any optional automated fluff Apps, such as iTunes Helper, to improve system performance.

Users & Groups

I recommended that you upgrade iTunes with a high-performance music/media player Application.

Disabling Automatic Software Update:

Go into the  Apple Menu, select System Preferences, and click on App Store. Uncheck the Automatic Updates box.

App Store 2

Note: This is the same place you can manually check for updates.

I cannot recommend more strongly that before updating you always make and test (yes, test) a backup of your drives.

App Store

Often updates have bugs or conflicts with drivers. Having a bootable backup allows you to easily return to your former working system, when as is quite common, an update screws up your computer : P

Repairing disk permissions:

For optimal system performance, Repair Disk Permissions after you do OS X updates, do Application updates, or transfer large quantities of data. This is a good habit to get into.

You can find Repair Disk Permissions in your Disk Utility Application.

Launchpad

Activate your Launchpad. Disk Utility is located in your Other folder.

Yosemite Other

Note: use the Escape key on your keyboard to return from the Other folder to the rest of your Launchpad Applications.

Disk Utility 3

To Repair Disk Permissions, simply highlight the disk you want to repair.

Disk Utility 2

When repairing disk permissions is done, you will see Permissions repair complete at the bottom of the Show details window.

Disabling the Time Machine automatic backup:

Go into the  Apple Menu, select System Preferences, and click on Time Machine.

On the left side of the window, you’ll see a slide selector that has off at one end and on at the other. Make sure the selector is switched off.

Time Machine

Warning! Your drive will inevitably fail: back up often. Using a bootable backup will save you a significant amount of time when you have to reinstall your boot drive.

Disable the automatic journaling feature:

Just as before, launch Disk Utility by activating Launchpad, clicking on the Other folder, and selecting the Disk Utilities icon.

Individually select any drive on the list. Hold down the Option button on your keyboard and click on the File drop-down menu. Slide down the File drop-down menu and select Disable Journaling. If you don’t hold the Option button down while selecting the File drop-down menu, Disable Journaling will not be a selectable option.

Disable Journaling

Repeat this for all drives.

If you wish to enable the automatic journaling feature for a drive, simply repeat the above process and select Enable Journaling in the same drop-down menu.


Turn off wireless control interfaces:

Turning off unused wireless control interfaces, such as WiFi, Bluetooth, and Infrared, improves performance by freeing up system resources and reducing data corruption caused by EMI “noise” on sensitive internal circuitry.

Systems Mojo Audio sells with our optimized Yosemite have Infrared turned off because it’s rarely used and Bluetooth and WiFi turned on since they are often used to set up new systems. I recommend turning off as many wireless control interfaces as possible.

Warning! Turning off wireless control interfaces can disable control devices, such as your Apple Bluetooth keyboard/mouse/pad. I recommend a USB keyboard and mouse for setup and troubleshooting.

For highest performance use no wireless control interfaces:

  • Connect to the internet via Ethernet cable on a LAN.
  • Control your desktop computer with USB control devices.
  • Use your laptop’s integrated monitor/keyboard/pad.
  • Use cables to transfer data between computers and devices.

The second-best option is to use only one wireless control interface.

Let’s start by looking at what works with what so you’ll have a better idea of which wireless control interfaces you’ll want to turn off.

Control devices associated with wireless interfaces:

  • Most keyboards and mice = USB (wired or wireless)
  • Apple keyboard and mouse = Bluetooth
  • Apple and aftermarket remote controls = Infrared
  • iOS and mobile device remote control = Bluetooth
  • iOS and mobile devices remote desktop App = WiFi

The above list may differ from brand to brand or App to App and may even change over time. I recommend connecting a simple USB keyboard/mouse/pad and turning on/off wireless control interfaces one at a time and testing each of your control devices to confirm which works with which.

Note: Wireless devices that plug into USB have relatively low noise compared to WiFi or Bluetooth because they have external receivers, cause less EMI noise, and are better shielded from internal circuitry.

Turning on/off the infrared:

Go into the  Apple Menu, select System Preferences, and click on Security & Privacy.

System Preferences

Click on the Advanced button.

Security & Privacy

Off: Check the box next to Disable remote control infrared receiver. On: Uncheck this same box to activate the infrared receiver.

If a windows Lock icon is in the locked position, you must unlock it before making any changes. To unlock any window, click on the Lock icon; you’ll be prompted to enter your administrative password.

Note: The password for any Mojo Audio optimized system is “Mojo.”

Turning on/off the WiFi control interface:

Go into the  Apple Menu, select System Preferences, and click on Network.

WiFi Networking 2

Click on and highlight WiFi in the left column:

Off: Click on the Turn WiFi Off button. On: Click on the Turn WiFi On button.

Note: The color of the dot on the left of the networking interface goes from green to red when an interface is turned off and returns to green when turned back on.

Turning on/off the Bluetooth:

Go into the  Apple Menu, select System Preferences, and click on Bluetooth. Click on the Bluetooth status button. Note the status changes.

Bluetooth 2

Click on the Advanced button and additional Bluetooth options appear. Check or uncheck the options you want. Personally I uncheck them all.

Bluetooth

Note: So that Apple keyboards/mice/pads work with our new systems we leave the Bluetooth on. I would recommend switching to a simple USB keyboard/mouse/pad and turning all the Bluetooth off.


Deactivate processes using Terminal:

Warning: incorrectly entering code in the Terminal Application can permanently disable your computer. It could require that you reformat and reinstall your entire boot drive.

Did you test your bootable backup? Always a good idea.

The Terminal application is a text-driven command-line interface that allows you to communicate directly with the Unix-based operating system at the core of OS X Yosemite. Unix is the lowest possible level of human interface above machine language, giving the most streamlined and direct control over Yosemite.

I’ll show you how to use Terminal to remove Apps and processes that are set running by default when Yosemite boots up .

To launch the Terminal application, activate Launchpad, go into the Other folder, and click on the Terminal icon. The Terminal interface will appear. Now you are ready to enter commands into the command-line.

Yosemite Other

Tip: To minimize the potential for error, I recommend you copy the commands and paste them into the Terminal’s command-line.

Terminal

Remove Mission Control: copy/paste the following lines into Terminal’s command-line one at a time and hit the Enter key after each one:

defaults write com.apple.dock mcx-expose-disabled -bool TRUE [Enter]

killall Dock [Enter]

Remove Dashboard: copy/paste the following lines into Terminal’s command-line one at a time and hit the Enter key after each one:

defaults write com.apple.dashboard mcx-disabled -boolean YES [Enter]

killall Dock [Enter]

Remove Spotlight: copy/paste the following into Terminal’s command-line and hit the Enter key:

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist [Enter]

In order for the following command to take effect you’ll be required to enter your administrative password and hit the Enter key.

Note: The password for Mojo Audio optimized systems is: “Mojo.”

Remove Automatic Termination: copy/paste the following into Terminal’s command-line and hit the Enter key:

defaults write -g NSDisableAutomaticTermination -bool TRUE [Enter]

Finder is the main organizer in Yosemite. Unlike most applications which you can quit or Force Quit, the default settings in Yosemite will allow you to relaunch but not to actually quit Finder.

Terminal 2

Resetting Yosemite to quit  Finder: copy/paste the following into Terminal’s command-line one at a time and hit the Enter key after each one:

defaults write com.apple.finder QuitMenuItem 1 [Enter]

killall Finder [Enter]

Important! Quit the Terminal Application.

To maintain optimal performance, each time you reboot your computer, and each time you use Finder, you will need to follow the instructions below to manually quit the Finder Application. Since Yosemite needs at least one Application to be open before you can quit Finder, you’ll need to open your player or primary software first.

Click on the Finder icon in the dock.

Select the Finder column in the top drop-down menu next to the  Apple Menu in the upper left corner of your screen.

Quit Finder

Slide down to the bottom row and select Quit Finder.

You’ll know Finder is not running if the dot under the Finder icon in the dock is gone.


Reactivate processes using Terminal:

Reactivate Dashboard: copy/paste the following into Terminal’s command-line one at a time and hit the Enter key after each one:

defaults write com.apple.dashboard mcx-disabled -boolean NO [Enter]

killall Dock [Enter]

Reactivate Mission Control: copy/paste the following into Terminal’s command-line one at a time and hit the Enter key after each one:

defaults write com.apple.dock mcx-expose-disabled -bool FALSE [Enter}

killall Dock [Enter]

Reactivate Spotlight: copy/paste the following into Terminal’s command-line and hit the Enter key:

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist [Enter]

In order for the following command to take effect you will be required to enter your administrative password and then hit the Enter key.

Reactivate Automatic Termination: copy/paste the following into Terminal’s command-line and hit the Enter key:

defaults write -g NSDisableAutomaticTermination -bool FALSE [Enter]

Reactivate Finder: copy/paste the following into Terminal’s command-line one at a time and hit the Enter key after each one:

defaults write com.apple.finder QuitMenuItem 0 [Enter]

killall Finder [Enter]

Important! Quit the Terminal Application.


Perform periodic maintenance:

To maintain the highest level of performance and security, you must periodically do a few tasks manually:

  • Turn off the Finder application every time you open or reboot.
  • Close applications other than your player or primary software.
  • Clone or back up your media and documents as they change.
  • Repair disk permissions every time you rip or download files.
  • Update software only as needed – if it’s not broke, don’t fix it.
  • Always clone or back up your boot drive before updating.
  • Repair disk permissions after updating or installing Apps.

If you like what you read in this blog and are interested in getting more free tips and tricks, sign up for Mojo Audio’s Audiofiles blog. Also, sign up for our e-newsletter to get more useful info as well as coupons, special offers, and first looks at new products.

Plus, don’t forget to “like us” on Facebook.

Enjoy!

Benjamin Zwickel

Read More

Asynchronous USB looks to be the perfect solution

پنجشنبه 21 جولای 2016
/ / /

این متن عالیه :

http://www.thewelltemperedcomputer.com/KB/USB.html

http://www.empiricalaudio.com/computer-audio/technical-papers/

USB

Universal Serial Bus (USB) is a serial bus standard to interface devices. USB was designed to allow many peripherals to be connected using a single standardized interface socket and to improve the plug-and-play capabilities by allowing devices to be connected and disconnected without rebooting the computer (hot swapping). Other convenient features include providing power to low-consumption devices without the need for an external power supply and allowing many devices to be used without requiring manufacturer specific, individual device drivers to be installed.

http://en.wikipedia.org/wiki/USB

A nice story about the development of the USB interface: The D/A diaries: A personal memoir of engineering heartache and triumph by Hitoshi Kondoh.

USB is a computer bus like any other but for some reason it inspires people to make all kind of funny products.

Wedding

USB wedding ring

Introduction

USB audio is very popular.
One of the reasons is that USB audio is part of the USB standard and as a consequence native mode drivers are available in all the popular OS (Win, OSX and Linux).
Connecting a USB audio device is a matter of plug&play.

USB audio is a flexible solution as any PC offers USB.

If you use a laptop this is probably the way to go if you want to improve on the on-board sound card.

The audio is routed to the USB.
This is a matter of choosing the USB audio device in your media player.
The on-board sound card is bypassed; in fact you don’t need a sound card at all.

The USB audio device is your (outboard) sound card.

 

Today the resolution of USB audio ranges from 16 bit/ 32 kHz to 32 bit/ 384 kHz.
A lot of DACs are still limited to 16 bit/ 48 kHz max.

 

The data transfer from the PC to the DAC can be done in adaptive or in asynchronous mode.
In adaptive mode the DAC adjust its timing to the rate the data is pouring in.
In asynchronous mode the DAC keeps its timing constant and controls the amount of data send by the PC. By design asynchronous mode eliminates input jitter.

Resolution

A lot of people think USB audio is limited to 16 bits/48 kHz max.
A lot of (cheap and sometimes not so cheap) USB DACs are indeed limited to this resolution.

This is because the manufacturer decided to use a simple and cheap of the shelf hardware solution.

Another common misunderstanding is the specification of the bus (USB 1,2 or 3) and the USB audio standard (1 or 2).

USB Audio Class 1 standard (1998)

This standard allows for 24 bits/96 kHz max.
The standard itself doesn’t impose any limitation on sample rate.
Class 1 is tied to USB 1 Full Speed = 12 MHz
Every millisecond a package is send.
Maximum package size is 1024 bytes.

2 channel * 24 bit * 96000 Hz sample rate= 4608000 bits/s or 576 Byte/ms
This fits in the 1024 byte limit.
Any higher popular sample rate e.g. 176 kHz needs 1056 bytes so in excess of the maximum package size.

 

All operating systems (Win, OSX, and Linux) support USB Audio Class 1 natively.
This means you don’t need to install drivers, it is plug&play.
All support 2 channel audio with 24 bit words and 96 kHz sample rate

USB Audio Class 2 standard (2009)

It is downwards compatible with class 1.
USB Audio Class 2 additionally supports 32 bit and all common sample rates > 96 kHz
Class 2 uses High Speed (480 MHz). This requires USB 2 or 3.
As the data rate of High Speed is 40 X Full speed, recording a 60 channel using 24 bits at 96 kHz  (132 Mbit/s) is not a problem.

From mid-2010 on USB audio class 2 drivers are available in OSX 10.6.4 and Linux.
Both support sample rates up to 384 kHz.
It is unclear if Microsoft is going to support USB Audio 2.
You need a third party USB class 2 driver on Windows.

Companies like Thesycon or Centrance have developed  a USB Class 2 Audio driver for Windows.

Using High Speed USB for playback  there are no limits in resolution.

USB Speed

  • Superspeed – 10 Gbps USB data rate (USB 3.1)
  • Superspeed – 5 Gbps USB data rate (USB 3.0)
  • High Speed – 480 Mb/s with a data signalling tolerance of ± 500ppm (USB 2).
    This means every 125 µs a SOF packet arrives with a allowed deviation of ± 0.0625 µs..
  • Full Speed – 12 Mb/s with a data signalling tolerance of ±0.25% or 2,500ppm. (USB 1&2)
    This means every 1ms a SOF packet arrives with a allowed deviation of ± 500ns.
  • Low Speed – 1.5Mbits/s with a data signalling tolerance of ±1.5% or 15,000ppm (USB 1&2)

USB receivers

The data send over the USB must be transformed to a format a DAC (the chip doing the DA conversion) does understand. This can be SPDIF or I2S.
This is the task of the receiver chip.

Adaptive mode 16 bit units often use the Cmedia or TI (PCM270x) based chip sets. These are not programmable and usually only support 16 bit  and 32, 44.1, 48 kHz sample rate.

An example of how this chip-set performs compared with asynchronous USB can be found below.

24 bit adaptive mode DACs needs a programmable design (TAS1020 or other USB Audio Controller).

This chip enables 24 bit/ 96 kHz over USB.

Chips like the TAS1020 are limited to full speed.

You can’t do high speed as needed for USB audio class 2.

96 kHz is the upper limit when using native mode USB Audio Class 1 drivers.

A USB audio class 2 or a custom driver is needed to run 176/ 192 kHz and higher.

An example is the Tenor TE8802L by Galaxy Far East Corp.

 

  • USB2.0 Audio Class v2.0 and v1.0
  • 2-Inputs support by one I2S pairs with 128/256 Fs.
  • 2-Output support by one I2S pairs with 128/256 Fs
  • Adaptive/Asynchronous Mode supported
    • High-Speed mode support Adaptive/Asynchronous
    • Full-Speed mode support Adaptive only
  • Resolutions support 16/ 24Bit with sampling rates support 44.1/48/88.2/96/176.4/192KHz
  • Built in one IEC60958 professional 24 bit/96KHz S/PDIF RX, with I2S pins as well.
  • Built in one IEC60958 professional 24 bit/192KHz S/PDIF TX, with I2S pins as well.

 

Today you can buy complete USB-receiver modules like XMOS.

Basically a USB to I2S or SPDIF converter.

A couple of these interfaces can be found here.

Transfer modes

Data is exchanged over USB using one of the four possible modes:

  • Control Transfers: command and status operations,
  • Interrupt Transfers: device requires the attention of the host
  • Bulk Transfers: large volumes of data like print jobs
  • Isochronous Transfers: time sensitive information, such as an audio or video stream
    • Guaranteed access to USB bandwidth.
    • Bounded latency.
    • Stream Pipe – Unidirectional
    • Error detection via CRC, but no retry or guarantee of delivery.
    • Full & high speed modes only

Transfer modes explained in detail.

Isochronous transfer

When the computer sends the audio stream to an USB port, if first reads the data from the hard disk and caches blocks of the data in memory.

It is then spooled from memory to the output port in a continuous stream (Isochronous mode).

Frames are sent out every millisecond.
This happens whether there is any data in the frame or not.
The rate at which the frames go out is determined by a oscillator driving the USB bus.
This rate is independent of everything else going on in the PC.
In principle this guarantees a constant flow of the frames.
In practice the frames might not be filled properly with data because some program simply hogs the CPU or the PCI.
Anti virus polling the internet at high priority are a well known example.

 

Isochronous transfer can be done with three possible types of synchronization modes in the USB audio device.

Synchronous, adaptive and asynchronous synchronization

There must be some kind of synchronization between the PC and the DAC to avoid buffer under/overrun.

Synchronous

The clock driving the DAC is directly derived from the 1 kHz frame rate.
This mode was used by the early USB audio devices.
They were limited to 48 kHz and pretty jittery.

Adaptive

In this mode the timing is generated by a separate clock.
A control circuit (sample rate guesser) measures the average rate of the data coming over the bus and adjusts the clock to match that.
Since the clock is not directly derived from a bus signal it is far less sensitive to bus jitter than synchronous mode, but what is going on the bus still can affect it.
It’s still generated by a PLL that takes its control from the circuits that see the jitter on the bus.

adaptive1

Asynchronous

In this mode an external clock is used to clock the data out of the buffer and a feedback stream is setup to tell the host how much data to send.

A control circuit monitors the status of the buffer and tells the host to increase the amount of data if the buffer is getting too empty or to decrease if it’s getting too full.
Since the readout clock is not dependent on anything going on with the bus, it can be fed directly from a low jitter oscillator, no PLL need apply.
This mode can be made to be very insensitive to bus jitter.

async1

 

The warm reception in the audiophile world of asynchronous USB as developed and promoted by Wavelength inspired other brands to offer asynchronous USB DACs .

 

Asynchronous mode is not better by design but by implementation because you can implement a top quality (low jitter) clock in the DAC.

There is actually a good example of this case of its the implementation of the clock thats important, not the asyncness itself that is important. The recent inexpensive Musiland devices use an asynchronous protocol but then use a frequency synthesizer to generate the local clock rather than use a fixed frequency oscillator. The result is jitter that is actually worse than some of the better adaptive implementations!

John Swenson

The best way to get the most out of a dac chip is to put 2 audio oscillators right next to the dac chip. Buffer the oscillators and send them back to the USB controller to use to create the I2S (or other audio data stream L/R justified, DSP whatever) and this will give you the best response and the lowest jitter.

 

What many companies are doing is using the Frequency Synthesizer to create the audio oscillators. Basically these are frequency multipliers that can create any frequency and in the case of the TAS1020 down to 4Hz resolution. The problem with a Frequency Synthesizer is that the jitter can be as much as 100x that of a fixed oscillator. When enabling the oscillator in the TAS1020 also adds noise to the audio data stream because of the noise it fixes to the power supplies.

 

So choose wisely what you buy and ask the correct questions.

It’s not about the code… though all of ours is different, it may have an effect on the sound. But more so it has to do with the hardware and how that functions.

Thanks
J. Gordon Rankin

 

Not everybody agree that asynchronous is better.

Centrance, manufacturer of adaptive mode solutions, is one of them.

Some manufacturers may lead you to believe that Asynchronous USB transfers are superior to Adaptive USB transfers. This no more true than saying that you “must” hold the fork in your left hand. If you know what you are doing, you will feed yourself with either hand.

Michael Goodman, Chief Product Architect

Async USB provides a simpler way to implement a low jitter DAC relative to adaptive mode USB. For the cost of a small number of lines of firmware code, you reduce the amount and complexity hardware needed and potentially reduce the cost of the hardware needed for a high quality result. Most thinking engineers appreciate simplicity and the potential for low cost designs that deliver the goods.

You can find plenty of bovine excrement in the marketing of all kinds of high-end gear. Marketing products using buzz words without supporting detail or test results works when the audience is technically ignorant.

Old Listener

The perfect solution

Asynchronous USB looks to be the perfect solution.
You configure your PC for bit-perfect output and the DAC takes care of the timing totally independent of the timing of the PC.
But there are posts on the Internet claiming that even in case of an async USB DAC what is happening upstream is still affecting sound quality.

 

Almost all recent offerings of quality DACs have asynchronous USB input.

 

One issue with USB is that it sends regular bursts of info like the start of frame packet – “The SOF packet consisting of an 11-bit frame number is sent by the host every 1ms ± 500ns on a full speed bus or every 125 µs ± 0.0625 µs on a high speed bus”. If the timing of this shifts or is variable, this could elicit a different & variable reaction from the USB receiver & translate into a different & varying jitter or noise spectrum. Making the PC end as solid & stable as possible without undue processing could be one factor in ameliorating this variation. It might not be the low level of jitter that we notice but the variation in jitter – that’s one reason why I say that the measurements we currently run seem not to be capable of picking up these issues or we are not directing them to the correct target for measuring.

Jkeny

Vendor specific

Some companies don’t use USB audio in isochronous transfer mode.
They implement their own solution using bulk mode transfer.
Bulk mode is asynchronous by design.

As it is bulk mode,

  • No guarantee of bandwidth or minimum latency
  • Error detection via CRC, with guarantee of delivery.

In case of isochronous mode it is exactly the reverse.

As long as the DAC is the only one connected to an internal hub, bandwidth is in general not the problem using USB high speed mode.

 

Inherent to a vendor specific solution is that he either supports your OS or not.
The advantage of USB audio is that it is natively supported by Win, OSX and Linux.
However in case of USB audio class 2 on Win you need a third party driver too.

Anyway this solution does audio over the USB without using the USB audio of the operating system.

 

Measurement

Jim Lesurf did a nice experiment.
He measured the analog out of a DAC Magic when feed by its own adaptive mode USB and by a asynchronous USB to SPDIF converter (Halide).

The differences between adaptive (USB direct) and asynchronous (Halide) are clear.

According to the author not only measurable but also audible. [5]

Archimago [11] measured the jitter performance of a adaptive mode USB and a async mode.

adaptive mode USB

 

Asynchronous mode USB (CM6631A

Indeed, the jitter performance improves with asynchronous USB

USB cables

Cable length between full speed devices is limited to 5 meters. For a low speed device the limit is 3 meters.

As the signal degrades proportional to the length of the cable, a short cable is often recommended.

Other says this can put a source of RFI (the PC) to close to the USB-DAC.

Audiophile USB cables

As file based audio is gaining momentum and many believe asynchronous USB the way to go there is a growing market for audiophile grade USB cables.

The question of course is why a cable can have any impact on sound quality.
Some say that improved jitter performance of a cable can make a difference.
Others say that the reason we use asynchronous USB is exactly to have zero input jitter at the DAC so all what is happening upstream is irrelevant cable included.[1]
Audiophile USB cables are becoming as controversial as high-end power cords.

The Limitations of digital audio processors and cables create timing errors known as jitter, which remove portions of the audio signal and replace them with noise and distortion. Cables tend to round off the square waveforms of the signal, making them less clear to the processor, thus increasing jitter. This rounding effect varies greatly among cables and a truly superior digital audio cable can make great improvements in sound quality.
http://www.wireworldcable.com/categories/usb_cables.html

 

Another manufacturer talking some marketing bull shit?
They do have a point.
Digital is indeed sending fully analogue electrons over a wire.
And indeed, the block pulse degrades with the length.
A good digital cable is one who minimizes this degradation.

The USB 2.0 specification lists a maximum cable length of 5 meters (~15 feet). This is marginal with the best of cables, and many “audiophile grade” cables will run into problems even with far shorter lengths. There have been many credible reports of improved sound quality with some cables, but these have almost all been in systems using Class 1 Audio, with a maximum data rate of 12 MHz. When the data rate is boosted by a factor of 40x to 480 MHz, there are very few “audiophile” cable companies that have the tools and experience to ensure good results.
Computer Audio Playback Overview – Ayre

This is an easy test.
Connect your high speed USB device, e.g. a hard disk using your audiophile grade USB cable. If hi-speed mode (480 Mbps instead of 12 Mbps, the old USB 1 standard) fails, it is a bad DIY digital cable not even compliant with USB 2 standards.

Configuring

A clear and well written step by step guide to setup and USB DAC using XP, Vista or OSX can be found at the Ayre website.

Setup for Win7.

Setup for Vista.

Check

You can check if your asynchronous USB DAC is really asynchronous.
Audio devices supporting asynchronous transfer mode should have an extra ‘endpoint descriptor’ with
bmAttributes = 0x5 (USB_ENDPOINT_TYPE_ASYNCHRONOUS).

Svyr has more

A simple way to find out is to use the Thesycon USB Descriptor Dumper

Drop out.

Some users complain about dropouts when playing USB audio.

This might be due to different devices sharing the same USB-Hub.

If your audio and your graphics card are on the same hub, the bandwidth required by the graphics might cause the audio to stutter.

Anti-virus programs polling the internet with high priority might interrupt the audio too.

Trouble shooting

Trouble shooting USB audio is covered here.

References
  1. Universal Serial Bus – usb.org
  2. USB audio spec and jitter – John Swenson
  3. How USB Works – Tech-Pro.net
  4. USB in a NutShell – Byond Logic
  5. Time for a change? – Jim Lesurf
  6. Universal Serial Bus Device Class Definition for Audio Devices 1 – Universal Serial Bus (1998)
  7. Universal Serial Bus Device Class Definition for Audio Devices 2 – Universal Serial Bus (2006)
  8. USB audio standards – Computer Audio Asylum
  9. How can USB performance impact audio quality? – Computer Audio Asylum
  10. Confirming whether your DAC is asynchronous as claimed or not – svyr
  11. MEASUREMENTS: Adaptive AUNE X1, Asynchronous “Breeze Audio” CM6631A USB, and Jitter – Archimago’s Musings
  12. USB made simple – MQP Electronics Ltd
  13. Fundamentals of USB Audio – Henk Muller, Principal Technologist XMOS Ltd. -June 27, 2012
  14. CYCLIC REDUNDANCY CHECKS IN USB – USB Implementers Forum
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CEC DA 0 3.0

چهار شنبه 20 جولای 2016
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این برند CEC آمده ایران و رومی از CEC استفاده میکنه به عنوان ترنسپورت. تو انگلیس هم Living Voice محصولاتش رو با این CEC دمو میکنه با Audio Note ژاپن.

ما هم این ترنسپورت رو شنیدیم و تفاوتش رو دیدیم چقدر زیاد بوده با ترنسپورت های دیگه.

حالا این CEC اومده یه Dac زده که روی کاغذ خیلی وسوسه کننده است. مالتی بیت ، R2R بدون هیچ چیپ تبدیل ، بدون فیلتر خروجی و …

نگاهی بهش بندازید جالبه :

http://www.cec-international.com/PAGES/s25.html

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Computer Audio

جمعه 15 جولای 2016
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نتایج من تا این لحظه (بعد از 30 ساعت مطالعه) این بوده در عمل بهترین گزینه USB هست (دقت کنید فقط USB 2 و USB 3 خوب هستند و گزینه USB1 مناسب نیست) بصورت Asynchronous و استفاده از یه کابل خوب مثل پیوریست و اینکه استفاده از ری کلاکر و واسط های حذف نویز اصلا خوب نیست. بهتره از مک استفاده بشه با نرم افزار بیت پرفکت Audirvana با تنظیمات مربوط. کل دیتای فایل موزیک باید تو حافظه باشه.

بعضی ها معتقدند بهتره از Toslink اپتیک برای ایزوله کردن استفاده کنیم که من حس میکنم راه حل USB (با پیشرفت بیشتر USB در آینده) راه حل بهتری خواهد بود. خود تورستن هم میگه این راه حل خیلی Jitter داره و اصلا خوب نیست.

راه دیگه هم Firewire هست که عملا نه DAC سازان رفتند سمتش و نه تو مک بوک خیلی بهش توجهی شده. این راه حل خوبه اما خیلی برای ماها عملی نیست و بیشتر بدرد استودیوها میخوره و برای پهنای باند بالا خوبه. راه حل PC با کارت صدای AES یا Firewire و سیستم لینوکس هم خیلی در موردش به نتایجی کسی نرسید که بخواد توضیحی به ما بده. عملا بهترین حالت استفاده از پورت یو اس بی MAC هست با Audirvana. خوبی دیگر Usb نسبت به Firewire در سادگی و نداشتن درایور هم هست.

هارد چه SSD چه معمولی خیلی فرقی روی ماجرا ندارند اما SSD کمی بهتره. برق یا باطری روی کامپیوتر مهمه و خودم ترجیح میدم از یک Power Supply خوب استفاده کنم.

موضوعی که مهمه اینه که تو انتخاب DAC باید به نکات زیر دقت کنیم :

  • اون DAC حتما ورودی USB 2.0 یا USB 3.0 داشته باشه
  • ورودی USB مبدل DAC حتما باید حالت Asynchronous گوردون داشته باشه مثل Wavelength یا Ayre یا Berkeley USB Alpha
  • باید ورودی USB اون DAC سیگنال رو مستقیما به چیپ DAC برسونه و نیاد اول به SPDIF تبدیلش کنه چون کل ارزش USB به همون Jitter کم Asynchronous mode هست و اگر بخواد تبدیل به SPDIF بشه دیگه کار خراب میشه.

دقت کنید نقش کابل USB برای کاهش نویز از PC به DAC بسیار مهمه.

از سایت رومی این لینک رو دیدم که مصاحبه های سال 2013 هست.

 

http://www.positive-feedback.com/Issue41/ca_intro.htm

Larry Moore and Eric Hider of Ultra Fi Audio Designs

Andreas Koch of Playback Designs

Tony Lauck

Steve Nugent of Empirical Audio

Gordon Rankin of Wavelength Audio

Jon Reichbach of Sonic Studio/Amarra

Vinnie Rossi of Red Wine Audio

John Stronczer of Bel Canto Designs

Daniel Weiss of Weiss Digital Audio

Vincent Sanders and John Hughes of VRS Audio Solutions

Kent Poon of Design w Sound

Charles Hansen of Ayre Acoustics

Pete Davey of Positive Feedback Online

رومی میگه جای نظرات Dan Lavry,  Ed Meitner, Michael Ritter and Pflash Pflaumer هم خالیه. شرکت های Lavry Engineering و  EMM Labs و berkeley audio design .

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Asynchronous USB DAC Bit-Perfect NOS Tube Non-Oversampling No Filter

جمعه 15 جولای 2016
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نتایج ما از یک سورس دیجیتال خوب تو میکرو :

  1. در صورت استفاده از کامپیوتر ورودی یو اس بی USB (نسخه های 2 و بالاتر) بهتر از SPDIF و بقیه ورودی ها هست اگر USB خوب پیاده سازی بشه بصورت آسینکرون Asynchronous USB و حذف نویز کامپیوتر . اینو هم تورستن میگه هم گوردون طراح Wavelength
  2. بیت پرفکت بودن یعنی آپ سمپل نشدن NOS (Non-Oversampling) و عدم استفاده از فیلتر دیجیتال و بطور خلاصه هیچ تغییری روی دیتای دیجیتال ندادن. این موضوع رو هم Peter Qvortrup طراح Audio Note و 47Lab میگه و هم رومی و تورستن (طراح AMR) و طراح Lampizator (آقای Lukasz Fikus ) خیلی روش تاکید دارند و طراح Wavelength (آقای Gordon Rankin) هم همین اعتقاد رو داره. همه اینها با دستکاری دیتای دیجیتال و هر نوع پردازش حتی ساده مخالفند. تمام DSP ها کارشون دستکاری دیتای دیجیتال هست.
  3. عدم استفاده از op-Amp و فیلتر خروجی و در مقابل استفاده از خروجی لامپ و ترانس که Tim طراح EAR و طراح Audio Note و طراح Lampizator بهش اعتقاد دارند.
  4. برق Power Supply خوب
  5. حذف کامل جیتر Jitter

در مورد این DAC USB شرکت Wavelength Audio بیشتر بخونیم :

Cosecant USB DAC by Gordon Rankin

http://www.6moons.com/audioreviews/wavelength3/cosecant.html

  – The Cosecant v3 connects the USB controller to a DAC module. The USB firmware to run that DAC module resides there so each module has its own developed code. The output of the module connector is sent directly to the 6GM8/ECC86 dual triode output tube, which drives the transformer-coupled output.
– The Cosecant has an external power supply with IEC connector to isolate the power from the DAC and its audio transformers.
– This is my own design and I wrote the software (1,800 lines of code for the USB controller to do what it does) like no one else does on the planet.
– The DAC featured in this review uses Asynchronous USB mode as do the Crimson. The USB interface is bidirectional, and has built-in error correction and buffering at both ends; it is an asynchronous interface. Clocking synch problems associated with SPDIF are not present with USB. The result is that the data on the disk is identical to what is leaving the DAC all the time. At start-up, the DAC tells the computer it can handle 16 bit audio at 32K, 44.1K and 48K. Since the USB receiver only has to handle these 3 frequencies, the clocking to the DAC has almost no jitter. SPDIF actually has to be synched to the exact frequency of the transport (i.e. if the transport is working at say 44.0896K instead of 44.1K the DAC has to sync to that frequency). Therefore the jitter problems of SPDIF are all but eliminated. The result is a zero error protocol to link between computer and DAC, with ultra low jitter.
– None of these DACs use any type of operational amplifiers (opamps) in their design. The DAC module is the only solid-state portion of the overall DAC.
– The output stage of each of these products is the key design element which is responsible for their overall sound.
– These DACs incorporate the TDA1543N2 (select top 5%) DAC chips with passive I/V using Shinko Tantulum resistors in a configuration that does not use analog or digital filters. Some people call these NOS DACs or what I call zero DACs. The data input is the data output without any up/oversampling or other manipulation, which seems to make for a very analog presentation.

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PageIndex=1&postID=8265#8265

Well, I admit that I was clueless on the subject but I was intrigued and I consulted my engineering recourses.  It turned out that what I proposed above was not exactly accurate: for instance regular computers do not use I2S bas interface…

To make the long story short: For a computer the USB port is a devise of the same hierarchy as sound card and there is not different for a computer to where output stream: to a driver on the sound card or to the driver the sit behind the USP port designation. With identical drivers used the ASE/EDU interface has fundamentally lower jitter interface, where the min jitter for USB is not even included in the USB standard. So, with identical design (more of the time used) the USB has no chance to be superior.

There is a catch however. With proper design, when USB is made not for utilitarian purposes but for high quality transfer, the USB has internal chance to be way more advanced. The ASE/EDU is forward-only interface where stream flows only in one direction with data mixed with clock marks. The USB is full duplex or bi-directional interface where stream flows in both ends. This enables designers to put a clock that might everything on the receiver side (DAC) and let this clock to manage the USB’s and even reader timing. USB sends data in burps by requests of by scheduled timing, this marks all might be managed by receiver side clock. In ASE/EDU the receiver shell recognize the timing marks and PLL or re-clock data. In USB there are no needs for PLL or re-clocking as the data arrives at the marks of the original clock. The USB in this case acts like an elephant that sticks a long trunk to another devise and sucks juice… according to my consultants this USB implementation is the most proper way to do the things. Or course no one knows HOW the USB is managed even if a DAC has USB port…

The Cat

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