Importance of clocking

The issue with S/PDIF or AES "reclockers" is that you have two clocks arguing over what should the absolute clock rate be.

The DAC is forced to take one of two approaches: Abandon it’s internal clock or attempt to keep it’s internal metronome and "fix" upstream deviations from it’s own mechanism. This is exactly the thing pro clocks do, but only because there are upstream devices manipulating the data stream. They are there to stop an inevitable argument that arises as a result of a studio’s workflow. Home users HAVE no such arguments to solve, but can create them by adding upstream clocks.

Maybe the best of these situations is to use an Asynchronous Sample Rate Converter, like in the Schiits, but then you’ve got to deal with the fact that your DAC is no longer being given bit-perfect conversions.

In measurements done, I’ve seen original DAC jitter perform actually get degraded, and the signal looks like the upstream jitter PLUS the DAC’s original jitter signature.

Either use an integrated streamer/DAC or a streamer with a multi-second buffer plus USB / asynchronous communication with the DAC is the way to go IMHO.

I should point out, use whatever you want to which sounds good to you, but so far all I'm reading is a misunderstanding of how and why studio clocks work.  I'm going to go with the documentation from Benchmark and Mytek and say it's a bad idea.

@erik_squires 

for avoiding misunderstandings: In my case Dac, Etherregen and USB reclocker are all synchronised to the same Antelope 10m clock. When using AES or SP/DIF the DAC needs to rely on the incoming embedded clock signal whereas USB asychronous slaves the server‘s clock, so effectively my server is equally synchronised to the 10m clock.

The issue with S/PDIF or AES "reclockers" is that you have two clocks arguing over what should the absolute clock rate be.

The DAC is forced to take one of two approaches: Abandon it’s internal clock or attempt to keep it’s internal metronome and "fix" upstream deviations from it’s own mechanism.

How does the DAC know? What do you mean by 'abandon it's internal clock'? Are you talking about the external clock input of a DAC substituting its internal one?   Don't you agree that the better (more accurate with less jitter/noise) the incoming data on AES/SPDIF, the easier the job of the DAC's internal clock?

@greg_f   There are two different ways of dealing with S/Pdif.  One, very common way, is to adjust D/A clock to average frequency of incoming S/Pdif stream while another is to completely ignore S/Pdif clock, strip the data and send it to D/A converter at different rate (Asynchronous Rate Converter).  

In first case data is often oversampled being sent to D/A converter in exact multiples of received frequency, while in the case of Asynchronous Rate Converter, D/A conversion frequency and incoming signal frequency are independent.  My Benchmark DAC3 D/A converter runs always at 210.9kHz - no matter what signal frequency is (it was 110kHz in DAC1).

CDP output data can be buffered and sent at exact intervals since both buffer clock and motor speed come from the same source (quartz crystal), but receiving D/A converter has to be somehow synchronized, otherwise samples may be lost.  In older devices it was Phase Lock Loop (PLL) analog circuit adjusting Voltage Controlled Oscillator (VCO) - D/A conversion clock.  These days everything is digital, so PLL circuit is also likely digital.  Either way, in this scheme D/A conversion rate is not constant, but adjusted to average frequency of incoming S/Pdif stream.

@kijanki  Thanks for the explanation. My DAC is an older Weiss DAC202 that uses ARC. It has extensive fairly advanced PLLs (it uses a wider range digital PLL (I don't know its noise/jitter spectrum) and its output is fed to an further analog PLL to reduce the jitter of the first PLL. I believe both PLLs are implemented on a single DICE IC which was state of the art back then. I used to have a datasheet but I must have lost it during a move so I uncertain of the exact operation. The DAC uses older ESS converters and I think they always run at 1.536MHz. To complicate the clocking scheme further, the AES output of my source feeds a Trinnov ST2 Hifi (digital room correction device) which also uses a DICE generated clock and its AES output then goes to the DAC.  I need to refresh my memory!

My issue is that my DAC doesn't have a USB i/f and therefore I need a streamer with either an AES/SPDIF output or an additional DDC to convert the USB.

Your thoughts please?