This is nonsense...There's no such thing as 'pure' digital transmission, every transmission is analog.
To have bit perfect trasmission you need trasmission protocols with error correction, retransmission of data, etc.
Finally for streamed data you don't even need to trasmit and receive all the bits...all you need is to receive the great part of it in a timely manner.
There's no a single way to transmit audio via USB.
For instance you can transfer audio as a file but you'll need a buffer to seamlessly play it and it will not be realtime.
BTW Isochronous trasmission can be done both synchronous or asynchronous (the difference is in which clock the trasmission use)
If a system is digital, the bits are transmitted and received or not. There's no "in between." If the bits aren't transmitted and received, there's dropouts if and when the lack of transmission/reception exceeds data correction. You recite a nice slogan, but that's all it is.
Sorry, false.
If the analog transmission representing digital data can't be interpreted there's an error.
If the transmission protocol provides a method for retransmisson you can then request again the missing data.
You're supposing the protocol provides retrasmission, there are protocols that don't do it.
Nicer than: That's the beauty of digital. You transmit the bits or you don't. ?
BTW mine is not a slogan but a simple, plain fact that every electronic engineer (should) know.
Yes, dropouts, if the error is great enough to cause correction to fail. You'd have to really work at it to cause this to happen, though no doubt some high end cable peddler or ignorant diy-er could have managed the feat. A cheap USB cable from any normal retail outfit will work perfectly in this system.
Are we still in context?
Am I right in assuming there is no error correction at all?
regards
Am I right in assuming there is no error correction at all?
regards
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Hi Marce,
can you elaborate?
While it's obviously true that "digital transmission is digital transmission" (truism), at the physical layer you transmit analog waveforms representing digital data, like pulses, squarewaves or a limited set of continuously varying wave forms (passband trasmission).
So, at the physical layer, digital transmission is still subject to physics and so to errors, which can be handled, if needed, at higher levels by transmission protocols (error checking, error correction, retransmission).
The whole digital domain is actually an abstraction.
Where am I wrong?
yes my understanding of USB audio transmission was slightly wrong
Isynchronous (sp) is waht hte majority of DACs handle from what ive seen, data is streamed in 0s and 1's, the DAC doesn't care if what it receives is what's sent, it just handles the signal and converts it to analog.
Asynchronous (sp) is more like hte method for which you would transfer data which cannot be received incorrectly, the data is checked, and resent if necessary before being processed, there are Asynchronous DACs available after research, which in theory shoudl completely remove the need for an overpriced cable? should it not?
So, to summarize... if you have an isynchronous DAC, the quality of the cable can potentially affect the recieved signal. Can you hear it? that's another matter completely
I hope i have this right please feel free to correct me
Isynchronous (sp) is waht hte majority of DACs handle from what ive seen, data is streamed in 0s and 1's, the DAC doesn't care if what it receives is what's sent, it just handles the signal and converts it to analog.
Asynchronous (sp) is more like hte method for which you would transfer data which cannot be received incorrectly, the data is checked, and resent if necessary before being processed, there are Asynchronous DACs available after research, which in theory shoudl completely remove the need for an overpriced cable? should it not?
So, to summarize... if you have an isynchronous DAC, the quality of the cable can potentially affect the recieved signal. Can you hear it? that's another matter completely
I hope i have this right please feel free to correct me
I smell entrenched positions, time for some posters to look at the bigger picture.
2nd order effects exist, fact!
Cables can't filter the data, fact!
Data either passes with a high enough accuracy to completely recovered or it does not, this in independent of resending, fact!
It would be nice if someone who claims 'better' cables can make an audible difference could point to blind listening tests that back up that position. Surely if 2nd order effects were audible there must be some way to 'queer' a test to prove it?
That no manufacturer yet has points to the truth.
2nd order effects exist, fact!
Cables can't filter the data, fact!
Data either passes with a high enough accuracy to completely recovered or it does not, this in independent of resending, fact!
It would be nice if someone who claims 'better' cables can make an audible difference could point to blind listening tests that back up that position. Surely if 2nd order effects were audible there must be some way to 'queer' a test to prove it?
That no manufacturer yet has points to the truth.
Digital signal transmission is covered by digital engineering techniques, this appears quite often on this site, as a possible explanation for certain theory's. it is the wrong way to think, if you are transmitting digital signals you follow the rules and guidelines for such, whilst it is true that a digital wave is made up of numerous sine harmonics they are treated in a different way than analogue.
If you want to learn about working with digital signals read anything you can from the following two gentlemen, as Dr Bogatin says about digital "No myths allowed"
https://www.printedcircuituniversit...TSsid=gsg2p54fq28fubhi45js3mlvc3&toggleview=1
Signal Consulting, Inc. - Dr. Howard Johnson
beTheSignal.com
If you want to learn about working with digital signals read anything you can from the following two gentlemen, as Dr Bogatin says about digital "No myths allowed"
https://www.printedcircuituniversit...TSsid=gsg2p54fq28fubhi45js3mlvc3&toggleview=1
Signal Consulting, Inc. - Dr. Howard Johnson
beTheSignal.com
Isochronous asynchronous mode revolves around clock source, not error correction. It provides feedback to the transmitter controlling data transmission rate as reception clock is located at the receiver.
Hi Marce,
thanks for the links, I'll read with interest.
I do agree but why digital transmission should not be affected by noise, distortion, impedance mismatch and reflections, bandwidth problems, etc. ?
From what I've studied at school it is...sure digital transmission is by design less sensitive to such problems but still affected.
If the trasmission protocol have no error correction and/or retransmission, like isochronous mode, any trasmission error affect data.
thanks for the links, I'll read with interest.
I do agree but why digital transmission should not be affected by noise, distortion, impedance mismatch and reflections, bandwidth problems, etc. ?
From what I've studied at school it is...sure digital transmission is by design less sensitive to such problems but still affected.
If the trasmission protocol have no error correction and/or retransmission, like isochronous mode, any trasmission error affect data.
I would agree.
But it is still transmission of a digital signal. It is not transmission of an analogue signal.
Hi Andrew,
if you have trasmission errors in isochrounous data how can be data unaffected?
This IF is important. Do "audiophilically inferior" usb cable introduce errors in the data stream? I very much doubt it as these would be clearly audible.
The problem with usb transmission is usually not data. Data errors would require either a truly awful usb host or a terrible cable. Any decently built cable will see to that.
There could be some troubles with usb though. I'll list two from memory, feel free to add more:
- usb transmits power as well as data, the "quality" of the power and ground lines can affect the proper operation of the attached device (which are mixed digital-analog).
- many usb receiver chips are also providing the master clock, which can either be derived, more or less directly, from the usb stream itself (pure isochronous or adaptive mode) or not (asynchronous). In the first case, we're looking at problems similar to spdif wrt clock recovery (there's a wonderful - if somewhat dated - article about that somewhere online by Hitoshi Kondoh, who designed the pcm2702 for TI). In the second case (asynchronous), the quality of the usb stream becomes less relevant. Still, hf noise riding on the data lines might interfere with the proper working of the usb receiver IC (once again, a mixed signal affair, not pure digital) and, in fine, with the quality of the master clock.
In both cases, the cable could "in theory" play a role but:
- the low jitter (probably not audible) achieved by many adaptive (not even asynchronous) usb receivers show that common cables are providing a sufficient performance;
- in real life, I've experienced problems (like noise floor going up by 10's of db) coming from different usb ports (different computers, same computer but different workloads, etc), never from the usb cables;
- galvanic isolation and some rf filtering makes in either case much more sense in problematic setups than expensive cables (and it is quite cheap thx to the adum).
There could be some troubles with usb though. I'll list two from memory, feel free to add more:
- usb transmits power as well as data, the "quality" of the power and ground lines can affect the proper operation of the attached device (which are mixed digital-analog).
- many usb receiver chips are also providing the master clock, which can either be derived, more or less directly, from the usb stream itself (pure isochronous or adaptive mode) or not (asynchronous). In the first case, we're looking at problems similar to spdif wrt clock recovery (there's a wonderful - if somewhat dated - article about that somewhere online by Hitoshi Kondoh, who designed the pcm2702 for TI). In the second case (asynchronous), the quality of the usb stream becomes less relevant. Still, hf noise riding on the data lines might interfere with the proper working of the usb receiver IC (once again, a mixed signal affair, not pure digital) and, in fine, with the quality of the master clock.
In both cases, the cable could "in theory" play a role but:
- the low jitter (probably not audible) achieved by many adaptive (not even asynchronous) usb receivers show that common cables are providing a sufficient performance;
- in real life, I've experienced problems (like noise floor going up by 10's of db) coming from different usb ports (different computers, same computer but different workloads, etc), never from the usb cables;
- galvanic isolation and some rf filtering makes in either case much more sense in problematic setups than expensive cables (and it is quite cheap thx to the adum).
Don't mix problems, please.
In this moment we're discussing about digital transmission and if different cables can give different error rates.
I'm talking about about industrial cables which insures higher signal integrity, a measurable difference.
The USB certification ensure that all certified cables are compliant to a set of minimum specifications, not that they perform exactly the same or have the same error rate.
You can find a variety of industrial and cheap USB cables, using different AWG, different shielding, with and without ferrite rings, all of them USB certified.
Audibility is another matter and we already know there's no general agreement on it.
I am not mixing problems, I am talking about the same - chances of USB cables introducing bit errors.
Randomly changed bits in audio transmission are easily audible as loud cracks. The signal looses continuity. No need to discuss that, just try it. What the "superior" USB cables backers claim is a very different change - the typical blanket off, better instrument separation, etc. In no way could a random bit change (transmission error) result into such effect. A different noise level could, but that is a different topic
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