Computer Audio Asylum: RE: PC + Asynchronous USB DAC Question by play-mate

Hey needtubes,

There is a lot of confusion about what asynchronous drive mode is about, and I don�t claim to give you a last word on this, but look at it this way :

when a USB DAC is running asynchronous mode it runns it clocking on its own (reference-)clock.
In this way the DAC should only capture/request the data that is the music file from the computer.
Irrelevant how jittered this data is drawn from the computers software, an asynchronous connection should asure that this data will be processed and clocked at the best the DAC�s internal clock can do.
In such synchonisation the DAC is the "master" and the computer/software just follows suit; i.e. delivers the file data.

In other transfer modes (adaptive USB; S/PDIF) the computer "is sending" data with potential jittery clock sigfnals, and this jitter have to be removed by more or less effective PLL�s (jitter-reduction circuits).

Especially in the later typoe of transfer mode, it makes sense to configure the computer so, that it delivers a pure, un-interrupted stream of data. That�s some of the idea behind the cMP concept.
When the DAC however is designed as asynchronous, it should not be affected by any jitter from the computer.

A twist on this, is that cPlay (of cMP fame)is designed as true ASIO software, and, albeit that it works with the asio4all driver, it can not run as a fully asynchronous system unless the USB DAC comes with a bespoke ASIO driver that allows the DAC to synchronize/communicate the clocking with cPlay.

With the appropriate ASIO driver, cPlay can such become an integrated part of the DAC�s own DSP.
In such way cPlay "hangs on"(is slaved) as pure data delivery, and nothing is clocked or synchronized before data reaches the D/A concerter.
In this case, the data timming issue (jitter) becomes almost irrelevant.

Only few DACs come with propritary driver software (even asynchronous ones) and I presume that this is caused by the substantial cost of developing such software, and that most consumer DACs will be hooked up to streaming clients anyway. These are not quite as prone to jitter as computers are, and not designed for installing communication (protocoll) software anyway.

hope it clears this subject a bit....

kind regards