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In Reply to: RE: Improved Regen sound posted by jkeny on November 24, 2015 at 04:01:23
I don't doubt the perceptions, but the theory seems somewhat incomplete. The problem is that the clock is the USB bit clock. Phase noise has nothing to do with phase noise modulating the audio clock, because this clock is at a totally unrelated frequency. A possible theory might add that the regulator noise caused jitter in the USB bit clock affects the USB receiver circuitry's power consumption. This is related to John S's theory of how the REGEN works to improve sound quality, but as far as I know this is just speculation as there is no hard evidence of what is going on.
We do know that noise on the REGEN power can be coupled into the analog output of some DACs in the form of common mode noise. This noise appears at the packet clock rate (8 kHz), indicating that the regulation isn't sufficiently stiff.
It beats me why DAC designers don't deal with these issues. There is no excuse for any 8 kHz noise to appear in the output of any USB DAC, regardless of the input signal, assuming only that the input signal conforms to the USB specification.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Follow Ups:
Why the usb interface is used without recognising the noise problems?
Yes, Tony, sorry my theory was a more general observation about what the characteristic improvements in SQ I have perceived Vs what I believe is the underlying cause of them.I find that the solidity & pinpoint placement of instruments in soundstage seems to emanate from reduction in close-in phase noise although I haven't measured this. However, what often accompanies such reduction in phase noise is also a reduction in the playback system noise. So these two factors are often interwoven & difficult to separate. The reduction in general playback system noise gives an impression of better realism to the sonic illusion.
Now, how exactly these two possible mechanisms are the result of using the Regen & improved by the battery tweak, I'm not sure - it seems to me that improving the digital signal does result in improved sonics but by what mechanism, I'm not sure. My simplistic thinking was that improving the PS to the USB clock was contributing to a better formed USB signal waveform being output from the Regen. Of course improving the Regen's PS also reduces noise on the output signal of the Regen. So, again we have an intertwining of mechanisms.
JS's speculation on how the Regen works was dealt a significant blow, in my mind, when JW (John Westlake) revealed that there is no ramping up of current in the USB PHY when dealing with progressively worsening signal integrity of the USB signal - no such mechanism exists in USB 2.0 receivers, only in USB receivers designed to handle USB 3. So, although I was initially a supported of the JS theory of operation - it seems less accurate to me now
But then theory is great but observation comes first or as an ex prime minister of ours used to say - that works in practise, now let's see if it works in theory :)
As regards CM noise - it's a lesser known issue on USB audio devices - most designers only consider differential noise & conclude that the differential USB receiver will take care of that, mistakenly, in my view. CM noise just isn't often on their radar
Edits: 11/25/15
In these days of rapid accumulation of knowledge in just about everything, it seems that we are even less capable of resolving mutlti parameter issues in software/hardware performance. In fact, the reverse is the case in that we now seem to latch on one thing or another, and simply speculate.
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