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In Reply to: RE: flawed many of todays USB Audio interfaces posted by Dynobot on August 30, 2015 at 16:32:34
They love it as it adds a baseline cost of e50 with the usb card. Plus, of course, isolation bits and power supply with perhaps another e50. This means a retail cost of 6x base cost.
In mid-end cases, it is better and more economic to use spdif with relock and wave shaping. In high end cases 384k spdif can be had. Most computer based hardware spdif is junk, with little understanding of proper implementation.
Even some designers think that cheap phono plugs are ok, or are forced to use them.
Follow Ups:
"In high end cases 384k spdif can be had. Most computer based hardware spdif is junk, with little understanding of proper implementation."
There would still be a problem with the reclocker, if it requires adapting to the incoming clock rate, since this will require a variable master clock with attendant complexity and jitter. However, this could be easily fixed by adding a clock signal (could be in SPDIF format) from the DAC back to the transport and the transport could slave to this clock. Then the "reclocker" would just be a small shift register and there would be no need for a variable frequency master clock and phase lock loop circuitry.
There remains one additional problem: conveying the speed the DAC is to operate at which will change depending on file format. This can be done by having the transport select its local clock based on the file format and use this clock whenever the clock from the DAC is at the wrong rate, but when the DAC is at the correct rate switch to the external clock. The DAC does the corresponding thing, namely when it sees that the incoming clock isn't at the same speed as its master clock it switches the master clock to the appropriate speed. (There are some messy details that need to be worked out, viz. state diagrams with timed transitions and when the analog output is muted and unmuted.)
There are also issues of DSD unless one uses the DoP kluge.
Of course this requires compatible logic on both sides, i.e. proprietary to one manufacturer or some kind of a "standard". However, were this to be done it would be advantageous over using packet based mechanisms such as USB and Ethernet, since the basic mechanism used between a transport and a DAC would also useful for isolation mechanisms within a DAC. If you compare the number of logic gates needed for this scheme and compare it with the number needed to implement any USB, Ethernet, or other packet based scheme you will see that all of the packet based schemes are obscenely more complex. This means that they will all create obscene amounts of digital noise in the proximity of critical mixed-signal and analog circuitry and hence for high end sound quality there will have to be additional isolation after this obscenely complex circuitry, adding unnecessary cost.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Hey Tony how many Dac's operated in this optimal format that you suggest?
Dynobots Audio
Music is the Bridge between Heaven and Earth - 音楽は天国と地球のかけ橋
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