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In Reply to: RE: Thanks for the review, & postings: question posted by Tony Lauck on September 22, 2015 at 10:44:42
Thank you for that explanation......
It makes really good sense.
And, again, - depending on what you mean by isolation of the PHY processor, this indicates NOT a problem with the DAC, - but with the integrity of the USB signal coming from whatever transport. And dwelling on the PHY isolation for a moment, - are we talking about a physical shielding of something like ERS paper? Moving the PHY chip physically away from the rest of the circuit....
I intend neither crassness, nor sarcasm: but from most DAC reviews showing pictures, - the PHY transceiver chip isn't being physically isolated. Yet the DAC manufacturer seems is often "blamed" for what is a "problem" at the transport. When in fact, (and/or beyond the choice of which PHY processor), there isn't a lot a manufacturer can do.
Without going into the fact that we agree that running SPDIF has issues, - just different kinds: an external USB to SPDIF IF may not have the same issues if reclocking & converting is done well. In that case, the Regen theoretically would be less effective.
To be totally clear, on the basis of all the testimony, I am NOT saying that the Regen isn't a supere bloody awesome device: I am just trying to weed through some of the information, and get an indication which application of it is optimal...
Cheers,
"Asylums with doors open wide,
Where people had paid to see inside,
For entertainment they watch his body twist
Behind his eyes he says, 'I still exist.'"
Follow Ups:
The isolation would need to be outside of the chip, specifically on the data lines, the power lines and the clock lines. There would be packaging issues, e.g. the way the ground planes were laid out on the circuit board(s) and possible need for shielding, etc...
The DAC manufacturer is selling a digital to analog converter. It is the function of this device to take a digital signal and convert it to analog. This includes dealing with the reality that all digits are not equal, but reading them as if they were: 0 101110110 111 101 is the same number as 0101110110111101.
With an asynchronous USB connection, there is no transporation or timing provided by the so called "transport". This terminology goes back to analog tape recorders, where the transport did control the timing of the music. This is not how modern DACs work. There is no "transport". There is a digital storage device. In the absence of overrun errors or CRC errors on the USB cable, any sound quality differences that depend on the source are entirely the fault of the DAC and can be reduced just as effectively by removing them inside the DAC as removing them inside the computer. (Or removing them in between, as with the REGEN.) It may be more expiditious to improve the transport than redo the DAC, or it may not. However, if the DAC is sensitive to its transport it shows that the DAC is not properly acting as digital to analog converter.
This is made obvious by John S's explanation of noise being created by the PHY chip. That chip is inside the DAC and it is the DAC designer's fault if he has not taken into account the characteristics of the chips he specifies.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Thanks for the explanation.....
But a "DAC" is still a DAC if it uses USB, SPDIF, AES, all in the same device.
Indeed we have seen issues where the "not so great" implementation of USB sounds way worse than SPDIF. In the case of an external USB to SPDIF converter, we've seen varying degrees in SQ depending on device philosophy/configuration.
""There is a digital storage device.""
Yes, sometimes it's the same as the "player" software processing the digital file to be played back. Sometimes that digital storage device is an external hard drive or NAS: a container.
Because the computer is a different "type" of transport, doesn't mean that it's not a transport: it still sends the digital signal to the DAC to be processed.
""However, if the DAC is sensitive to its transport it shows that the DAC is not properly acting as digital to analog converter.""
The only way that that can be the case is with a partial or complete failure of DAC output to amplification. Clearly not the case, when a DAC performs better with it's AES input then it does with its USB.
What seems to me to make the above even more incorrect is that all DACs vary in sound quality whenever different USB ports are used on some USB buses: even well designed DACs. Or all DACs sound worse with ITUNES than they do with JPLAY. If the fault was in the DAC, (and not the quality of the waveform/signal it receives), then why does player software vary even on good DACs?
"Asylums with doors open wide,
Where people had paid to see inside,
For entertainment they watch his body twist
Behind his eyes he says, 'I still exist.'"
As far as I am concerned, when a DAC is used with different input circuitry it is, for all practical purposes, a different DAC.
My comments in this thread were with respect to USB DACs, specifically those that operate asynchronously. (If a DAC receives audio timing information from the same "box" as its digital samples, as is the case with SPDIF and many AES/EBU configurations, then indeed, I would agree that the device sending clock and data is a transport, since then the partition of functions between the two boxes is conceptually similar to the traditional two box CD players or for that matter a two box tape deck with heads and mechanicals in on box and electronics in the other.)
For a DAC to pass noise on its digital input through to its analog output is similar to a DAC passing noise on its power input through to its analog output. In both cases, if this noise is excessive (relative to the price point of the DAC) then the DAC is not operating properly. Another possibility is electrical noise from nearby devices. (I've not experienced this with a DAC, but of course it is common with analog sources if equipment is not located properly.) Here, by "noise" I include subtle changes to the music as well as clearly separate background sound.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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