USB audio transmission isn’t bit true

[mansr]

10 minutes ago, Arpiben said:

When an audio packet (max 1024 bytes) is detected faulty it is not discarded just played as it is.

That's not true.

[firedog]

On 11/27/2018 at 8:45 PM, beerandmusic said:

Gordon Rankin: What we have here is an explanation with screenshot proof that USB audio transmission isn’t bit true

Which without context is a meaningless statement. Something you seem incapable or unwiling to understand. 

[tmtomh]

On 11/27/2018 at 1:45 PM, beerandmusic said:

Gordon Rankin: What we have here is an explanation with screenshot proof that USB audio transmission isn’t bit true

 

And you wonder why others accuse you of repeating the same mantra over and over and not in any way changing your view when new information or evidence comes in.

 

If you are accused of something, and the accusation is true, you've no one to blame but yourself for the negative feedback you get.

[Arpiben]

1 hour ago, mansr said:

That's not true.

That was my understanding when dealing with asynchronous audio transfer. It can be DAC choice to discard the packet or not..

Do you mind elaborating, thanks.

 

[mansr]

6 minutes ago, Arpiben said:

That was my understanding when dealing with asynchronous audio transfer. It can be DAC choice to discard the packet or not..

Do you mind elaborating, thanks.

Damaged packets are detected and reported by the host controller. It probably depends on the hardware whether the payload of such packets is available at all. Even if it is, it would be quite foolish of a DAC to play bad data since it could easily result in very loud bursts with the potential to damage speakers. The XMOS based DAC I tested clearly drops bad packets without padding or interpolating.

[Sonicularity]

I wonder what the special mechanism might be and how the RME device goes about correcting a drop-out.   Maybe they are repeating the last known bit?  I suppose with a large enough buffer that other options would be available.

 

Quote

"The ADI-2 DAC features a unique data checking, detecting errors during transmission via USB and displaying them in the Settings dialog. "Additionally the ADI-2 DAC provides a special mechanism to continue recording and playback in case of drop-outs, and to correct the sample position in real-time."

 

http://www.rme-audio.de/download/adi2dac_e.pdf

[esldude]

2 hours ago, Sonicularity said:

I wonder what the special mechanism might be and how the RME device goes about correcting a drop-out.   Maybe they are repeating the last known bit?  I suppose with a large enough buffer that other options would be available.

 

 

http://www.rme-audio.de/download/adi2dac_e.pdf

If it displays errors, I wonder if it ever has any to show?

[botrytis]

On ‎11‎/‎28‎/‎2018 at 1:33 PM, JohnSwenson said:

There actually IS a difference. Music uses isochronous transmission which has NO error correction. Most other forms of data use transmission protocols which DO have error correction, thus transmission errors get corrected so the end user never sees an error. With music there is no correction so transmission errors DO show up at the DAC.

 

Per my previous post transmission errors are very rare with shorter cables, but do happen a LOT with longer cables.

 

So while in some sense data is data, how music data gets sent over USB is very different.

 

John S.

Not exactly. You are ONLY partly correct and that is the problem - from https://www.edn.com/design/consumer/4376143/1/Fundamentals-of-USB-Audio a small quote - Henk Muller, Principal Technologist XMOS Ltd.(this is from 2012).

 

"A single isochronous transfer can carry 1024 bytes, and can carry at most 256 samples (at 24/32 bits). This means that a single isochronous endpoint can transfer 42 channels at 48 kHz, or 10 channels at 192 kHz (assuming that High Speed USB is used - Full Speed USB cannot carry more than a single stereo IN and OUT pair at 48 kHz)."

 

This mean there is plenty of data that is transmitted and MORE data than most will listen to over USB. 

 

 

 

[fas42]

14 hours ago, beerandmusic said:

that was in his test case....there are literally a million different possibilities with different hardware and different environments...the point is that error rate can and will affect SQ...but again, I believe can be avoided with a "properly optimized system".  I think USB can be fine, but that it is subject to SQ issues....even when using a non-optimized multi function pc, i had hard time telling if i liked usb better than enet or visa versa...so with a well tuned usb system, i see no practical issues.

 

If one looks at things more closely, there are very obvious reasons why USB audio has sound quality issues, as often implemented. And it has zero to do with the digital "gettings the bits right" - how the receiver is set up, and feeds into the DAC, to me, is a rat's nest, guaranteed to cause SQ degradation. I looked at a few designs of what's out there, and I didn't like a single one of them - only someone who has scrupulously looked at, and considered every aspect of how the circuitry should operate is likely to get optimum quality from that part of the chain ... as you say, best is a solution that completely eliminates the USB link.

[Ralf11]

the DACs are not getting their bits accurately because the bits are being lost to gravitational leakage 

[Daccord]

6 minutes ago, Ralf11 said:

the DACs are not getting their bits accurately because the bits are being lost to gravitational leakage 

Either that or the USB cable shielding contains olestra.

[Arpiben]

4 hours ago, Sonicularity said:

I wonder what the special mechanism might be and how the RME device goes about correcting a drop-out.   Maybe they are repeating the last known bit?  I suppose with a large enough buffer that other options would be available.

 

 

http://www.rme-audio.de/download/adi2dac_e.pdf

 

Most probably it must be some kind of interpolation.

Otherwise in digital transmission you do have error correction mechanisms such as Vitterbi or/and Reed Solomon. But those supposed you send extra bits for error correction at receive side.

Such is not implemented in USB audio as far as I know.

[beerandmusic]

 

MANSR>> Damaged packets are detected and reported by the host controller. It probably depends on the hardware... The XMOS based DAC I tested clearly drops bad packets without padding or interpolating.

 

+1

I would rather a DAC drops errors so the errors are more obvious rather than interpolate, where you may not know...I don't want a DAC to interpolate... I say get it right first, without trying to fix...

 

I am glad that both sides agree that DACS get errors, that USB is subject to error rate because of isosynchronous transmission , and the errors can be a result of a number of different reasons...and it appears even in a very stable environment, that a dac can interpolate such that it would be difficult to hear....either way, a USB interface  is unnecessary, and enet may be preferred by many, including LUMIN, who now even offer a network player with fiber input....now we are talking!

[mansr]

2 minutes ago, Arpiben said:

Most probably it must be some kind of interpolation.

Otherwise in digital transmission you do have error correction mechanisms such as Vitterbi or/and Reed Solomon. But those supposed you send extra bits for error correction at receive side.

Such is not implemented in USB audio as far as I know.

If they use a custom protocol (not UAC), they could have some form of error correction. The quoted text does not really suggest that, though.

[asdf1000]

37 minutes ago, mansr said:

If they use a custom protocol (not UAC), they could have some form of error correction. The quoted text does not really suggest that, though.

 

Like Chord's Windows (ASIO) driver:

 

https://www.head-fi.org/threads/chord-electronics-hugo-2-the-official-thread.831345/page-867#post-14264276

 

[diecaster]

44 minutes ago, beerandmusic said:

I am glad that both sides agree that DACS get errors, that USB is subject to error rate because of isosynchronous transmission , and the errors can be a result of a number of different reasons...and it appears even in a very stable environment, that a dac can interpolate such that it would be difficult to hear....either way, a USB interface  is unnecessary, and enet may be preferred by many, including LUMIN, who now even offer a network player with fiber input....now we are talking!

 

USB is not subject to errors because of isosynchronous transmission. It can’t correct errors due to isosynchronous transmission. 

 

In the several dozen times I have tested for bit perfect transmission over USB with my DAC and various setups, I have never had it not be bit perfect. A proper USB setup should not see errors as a matter of course. 

[esldude]

51 minutes ago, beerandmusic said:

 

MANSR>> Damaged packets are detected and reported by the host controller. It probably depends on the hardware... The XMOS based DAC I tested clearly drops bad packets without padding or interpolating.

 

+1

I would rather a DAC drops errors so the errors are more obvious rather than interpolate, where you may not know...I don't want a DAC to interpolate... I say get it right first, without trying to fix...

 

I am glad that both sides agree that DACS get errors, that USB is subject to error rate because of isosynchronous transmission , and the errors can be a result of a number of different reasons...and it appears even in a very stable environment, that a dac can interpolate such that it would be difficult to hear....either way, a USB interface  is unnecessary, and enet may be preferred by many, including LUMIN, who now even offer a network player with fiber input....now we are talking!

Yes, we are glad you agree we all agree even though we don't just so you will feel okay about having a useless and wrong-headed conception about USB.  This way you can rationalize (to use the word loosely) your idea ethernet will be superior.  

[Superdad]

3 hours ago, Daccord said:

Either that or the USB cable shielding contains olestra.

 

No, olestra causes one to loose their sh*ts, not their bits.  

[esldude]

1 hour ago, Superdad said:

 

No, olestra causes one to loose their sh*ts, not their bits.  

He's talking about audiophile grade olestra.  Added for smoothness, but also may cause some coloration. 

[beerandmusic]

9 hours ago, diecaster said:

 

USB is not subject to errors ...

 

Do you use a fancy usb cable?

Dedicated PC?

Optimized PC?

Quality PC?

 

[diecaster]

I didn't say that USB is not subject to errors. I said that "A proper USB setup should not see errors as a matter of course."

 

I have used a variety of computers, including laptop, desktop, and server systems I have used "special" and typical USB cables shorter than 3 meters. I have not used an optimized system but always a quality system. I have used special purpose systems as endpoints. This would include the microRendu, the ultraRendu, and various SoTM endpoints.

 

You don't have to do any "special" to get reliable data transfer over USB. You just don't want to do anything unusual like use 6 meter USB cables or crappy endpoints.

[beerandmusic]

9 minutes ago, diecaster said:

I didn't say that USB is not subject to errors. I said that "A proper USB setup should not see errors as a matter of course."

 

I have used a variety of computers, including laptop, desktop, and server systems I have used "special" and typical USB cables shorter than 3 meters. I have not used an optimized system but always a quality system. I have used special purpose systems as endpoints. This would include the microRendu, the ultraRendu, and various SoTM endpoints.

 

You don't have to do any "special" to get reliable data transfer over USB. You just don't want to do anything unusual like use 6 meter USB cables or crappy endpoints.

 

Ok, i also see you are using an ultra rendu....I can accept that you have a reliable usb solution....I can agree that "A proper USB setup" should resolve for isosynchronous transmission. 

[diecaster]

I am using an ultraRendu now. But, in the past I have run a variety of systems directly the DAC with no special cables and there were no errors detected when I checked.

 

Again, USB 2.0 Audio is not inherently error prone. The premise in the title of this thread is just plain wrong.

[beerandmusic]

10 minutes ago, diecaster said:

I am using an ultraRendu now.

Why did you switch from pc direct connect to usb?

[diecaster]

You mean why did I switch from direct connect USB (computer to DAC) to a server/endpoint setup using USB at the DAC?

 

There were several reasons. One was that I wanted to stop using my office computer or my laptop to play music. I wanted a dedicated server for Roon so whatever I was doing on my computers did not affect music playback. Another was that I wanted the best sound quality possible and I knew that my noisy desktop and laptop systems talking to the DAC directly over USB was about the worst way to go in that regard. Some kind of special purpose endpoint was the way to go there. Finally, I wanted multiple "zones" to play music with all of them accessing the same music. The best way to do that was to have a Roon Core server with multiple "endpoints".