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In Reply to: RE: I expected more from you - apparently, was wrong. But that's OK. posted by carcass93 on June 18, 2013 at 10:20:57
There is no signal on a USB cable in between the packets. Nada. In this regard there is no difference in between two packets in the middle of a musical selection as after the final packet sent that complete a play list. There may be some measure of electrical activity on the wire at these times, but any variation about 0 would be called "noise" and not "signal".
In more detail, USB is designed so that several different devices can be connected to the same "bus" out of the computer. This works because the packets the computer sends are addressed as to the specific devices intended to receive it. When the computer is not sending to the DAC it may be sending to another device, such as a printer. (This might be a poor configuration for a high quality audio system, but it would probably play without glitches on most modern computers. This illustrates the point that transmission on USB is not continuous.) If you want to learn the gory details of how USB works, all the documentation is available on line, but reading it is a pretty dull way to pass a rainy afternoon. You will find sufficient details to see what waveforms are permissible at the input of a USB device. You will also find detailed specification of how much deviation is allowed in the waveforms a USB device must interpret as the same sequence of bits. This defines the amount of "noise" that the USB receiver is required to reject.
It is certainly possible that a DAC may have inadequate circuitry that causes it to respond to residual electrical energy at times when no data is being transferred. Indeed, it may have poor power supply noise rejection that causes it to be affected by residual noise on the power cable, such that a nearby computer affects it even if that computer isn't connected by USB to the DAC. However, if this happens it represents a defect in the DAC. The situation is not that different from what happens with noise on the power wiring, where susceptibility to this noise is obviously a defect and not a "feature". The power case is more clear cut to those who don't understand how digital signaling works but who do have some understanding of AC power wiring.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Follow Ups:
where else would there be impedance and other electrical parameters specified for usb transfer?
Weird concepts like 'when is a signal not a signal' form a barrier to rational discussion in this forum
"Weird concepts like 'when is a signal not a signal' form a barrier to rational discussion in this forum"
The key attribute of a signal is that it conveys information. A signal is a purposeful construct. Puffs of smoke from a fire are a signal if someone is using them to attract attention or send a coded message. Otherwise, they are just smoke.
See below.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
... a playback chain that includes async USB device, connected to that computer. This is true for ANY async USB device (DAC, converter) in existence, and the more resolving is the DAC and the system, the bigger the improvement.After such fact is established (and, don't know about you, but it IS established for me), you have to look for answers WHY - and "perfect 1/0", or "perfect on/off" theory that you're disseminating, is NOT helping the cause.
Edits: 06/18/13
"This is true for ANY async USB device (DAC, converter) in existence, and the more resolving is the DAC and the system, the bigger the improvement."You say that this is true for every Async device, but there are several designers who state that they have made improvements and are making additional improvements to their DACs that reduce the amount of these effects. Your conflation of "resolving" in a DAC with the ability to hear irrelevant differences is an indication of what is wrong with your approach. A "resolving" system should resolve what is on the recording, not extraneous noise that is in the environment. I would wager that as much of 50% of the differences that audiophiles think constitute "resolution" have nothing to do with playing what is on a recording, but very much to do with noting artifacts caused by their equipment limitations.
It may be a fact that today every currently marketed async USB DAC has these defects, but it doesn't mean that this is a necessary feature of every future product Furthermore, it doesn't necessary mean that changing computer systems is a better approach than making improvements to a DAC. IMO, if half the energy being spent by audiophiles improving their computer audio systems could be directed instead to manufacturers improving DACs, then I suspect we would all be in a better situation. For this to happen, audiophiles would have to start demanding that their DACs be immune to these problems.
For starters, I suggest that magazine reviewers be instructed to listen to a DAC using a variety of transports (computer or otherwise) and then to write their review based on how the DAC sounds with the worst sounding transport. Similarly, for those who place faith in measurements, those reviewers who publish measurements should measure only with input signals that just barely meet the USB specifications, conducting each and every measurement using that legal USB input waveform that makes the resulting DAC performance measure the worst possible.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Edits: 06/18/13
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