USB audio transmission isn’t bit true

[mansr]

18 minutes ago, beerandmusic said:

The actual bits won't be accurate at the input pin(s) to the dac....that is what many/most people try to sell you here, but it is untrue. A lot of things are logical to me now in realizing this.

The error rate of USB is actually very low in normal circumstances. This can be trivially tested by capturing the output of a USB to S/PDIF converter.

[mansr]

7 minutes ago, beerandmusic said:

Gordon Rankin

Gordon Rankin is not trustworthy.

[mansr]

10 minutes ago, esldude said:

Which I have done for hours and hours and hours never once getting an error.

A bit error rate of 1e-12 should be achievable. With 192 kHz 24-bit stereo audio, that's one error every 30 hours or so. Nothing anyone would notice.

[mansr]

33 minutes ago, sandyk said:

We aren't talking about the printing on a piece of paper where the letters aren't always 100% evenly spaced and it doesn't matter if the letters are a little blurred. Just try copying the contents of a forum page to notepad and you will often see just how imprecise looking this can be after digital copying, with some letters almost touching each other in many cases.

They still can't even prevent some letters that you type coming out in the wrong order.  In many cases it should be blindingly obvious that you couldn't possibly have spelled the word that way.

What on earth (or elsewhere) are you talking about?

[mansr]

5 minutes ago, yamamoto2002 said:

USB specification says, in the worst case 1 bit in 1000 000 000 000 bit may be corrupted.

That's for USB 3. The USB 2.0 spec doesn't mention any particular number. Of course, given the much lower data rate, achieving the same level there should not be a problem.

[mansr]

2 minutes ago, beerandmusic said:

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

I can provoke an error too if I use a sufficiently horrible cable. Or just wait a few days.

[mansr]

51 minutes ago, beerandmusic said:

 You can believe Rankin would do that, i don't...

He did. You provided the evidence. It's not interesting that he once observed an error. Only the error rate is meaningful.

[mansr]

6 minutes ago, beerandmusic said:

not disputing the error rate....just that it is not always bit perfect.

Of course there will be an error if you wait long enough. Nobody sane has ever claimed otherwise. What is claimed, and rightfully so, is that the error rate in practice is low enough as to be utterly irrelevant.

[mansr]

7 hours ago, JohnSwenson said:

I have done same tests that Gordon did and get similar results. Under some conditions you can get lots of data errors (many per second) with USB audio, under other conditions you can get no errors for days.

 

The biggest correlation I got was with cable length. With a cable greater than 3m you have pretty good chance of getting a large number of errors. Under 2m errors are few and far between (days between errors).

 

Between 2m and 3m is where the fun happens, you can trade off cable length and cable quality. For example with Supra cables you can go with significantly longer cables than cheap cables. In this range hardware has significant impact. For example my SuperMicro motherboard is error free with longer cheap cables than my cheap laptop.

 

I also did a lot of listening to the audio with different error rates on the USB. At low error rates the sound is identical. As error rates increase you start hearing the infamous clicks and pops. If you are getting say a click per minute, the sound quality in between clicks doesn't change. As the clicks come more often they get so annoying its impossible to tell if the sound quality is changing or not. At some point the errors come so often the system just shuts down, it can't handle that many errors. (a 5m cheap cable has a high probability of doing this).

 

So my conclusion was that if you stay with cables less than 2m you can be pretty sure you are essentially error free.

 

These rare bit errors do not seem to cause any sound change (other than a possible click).

That matches my own experience exactly.

[mansr]

What we have here is a failure to communicate.

[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.

[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.

[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.

[mansr]

6 minutes ago, davide256 said:

common OS/player USB error characteristics

USB typically has no errors. Assuming a perfectly realistic bit error rate of 1e-12, you get less than one bad packet per day of continuous playback.

[mansr]

12 hours ago, beerandmusic said:

I wonder why some designers are moving to bulk-pet over isosynchronous for DSD to shorten the audio latency.

 

https://www.itf.co.jp/prod/audio_solution/bulk-pet/bulk-pet-en

 

It is defined to using Isochronous Transfer to transmit the audio data in USB Audio Class.
Audio data is transmitted in a constant period in Isochronous Transfer.
On the other hand, huge proccessing loading also appears in a constant period on host CPU and device CPU.
This huge processing loading causes the sound quality slight changes.

Bulk Pet is the technology that transmitting the audio data in Bulk Transfer.
In Bulk Transfer, it’s able to control the transmission data volume and transmission frequency.

That's all complete nonsense.

[mansr]

3 minutes ago, diecaster said:

When will you get it that "Americans" refers to people of the United Stats of America?

 

https://en.wikipedia.org/wiki/Americans

From that article: The word "American" can also refer to people from the Americas in general.

[mansr]

12 minutes ago, sandyk said:

So Mansr must be a suave sophisticate

I've been called many things, but never that.

[mansr]

1 minute ago, audiobomber said:

Why the fixation with isosynchronous USB? Aren't most audiophile DAC's asynchronous?

Firstly, it's called isochronous. This means a fixed bandwidth from host to DAC is reserved, ensuring that it isn't starved of data due to other device activity. Transfers are scheduled at regular intervals. Isochronous endpoints can have any of several synchronisation types defined by the USB spec:

 

Most DACs use an asynchronous sink coupled with an adaptive source (the host computer).

[mansr]

1 hour ago, beerandmusic said:

you even provided me the links where MANSR was testing a fubar cable...besides this quote, he provided wav file and said buzzing and distortion also occurred besides skips...granted, he was using a fubar cable....

 

MANSR QUOTE>>>" When errors start showing up, it's as an occasional skip which is clearly audible. The thing is, as soon as a single bit is wrong, an entire packet is discarded, and this causes a huge error in the recovered data stream. "

 

But i don't entirely agree with the statement...., i agree with IFI that single bit errors can also cause distortion...and also don't think all dacs will drop the entire packet for a single bit error....more likely, if a packet is dropped you would hear a click/skip/dropout...but I also believe some DACS will interpolate and some will process even with errors...and clearly if it's just a single bit you likely would not even hear it....think many thousands of bits per second...you would not hear one bit...now if you have many crc errors and the dac doesn't drop the entire packet, you would have distortion....MANSR did state that he heard buzzing and distorted sound in one of his tests where there were many errors, so it sounded like in that thread, that he acknowledged that error rates can cause both distortion and dropouts....really depends on how the DAC manages the CRC errors.  Archimago also stated error rate can cause distortion in one of his blogs....again, i am not suggesting in an optimal normal setup, that this likely would occur....i am thinking it is more dependent on noise and computer interrupts.  Why else worry about things like running processes, buffer settings, and why would people suggest noise limiting cables and usb toys and reclockers etc...designed to minimize noise can help in some environments...it just depends on hardware, noise, buffer settings, computer interrupts, etc....many things can cause crc errors, but it has been proven by IFI that noise can impact CRC errors....and we all know now, that if there are errors, the packet will not be resent...the errors will be processed in one way or another by the dac.

This is just too funny.

[mansr]

29 minutes ago, Superdad said:

please don't pour your stream of consciousness into ours.

I think you mean maelstrom.

[mansr]

12 hours ago, sandyk said:

Most recent DACs use an asynchronous sink coupled with an adaptive source (the host computer) ?

Name one DAC using synchronous mode.

[mansr]

2 minutes ago, sandyk said:

The discussion at the attached link by Graham Slee may be of interest to some.

 

https://www.hifisystemcomponents.com/forum/isochronous-or-asynchronous_topic1887.html

He's got the terminology all wrong (synchronous, asynchronous, and adaptive are all subtypes of isochronous endpoints). I wouldn't trust anything that man has to say.

[mansr]

25 minutes ago, sandyk said:

Who can you trust if you can't even trust well known E.Es  ?.

( He was originally a BBC Engineer before going into business for himself)

I don't care if he's the Pope himself. When he can't get basic terminology right, he loses all credibility.

[mansr]

42 minutes ago, sandyk said:

That wasn't my point.

 Misinformation is spread by many Professionals.

 It then comes down to who can you trust, or is it because you need to source this information from Professionals who work specifically in these areas, and aren't Electronic " Jack of All Trades"  ?

Regarding USB, the best source of information is the actual spec. It's free to download.

[mansr]

9 minutes ago, sandyk said:

Like Gordon Rankin perhaps ?

What does he have to do with USB?