Improving on peripherals side

It will be up to the semiconductors manufacturers to improve on the performance of USB decoders, using more sophisticated PLLs and more powerful buffers, and/or software.

Nevertheless, three methods to improve on jitter performance on the side of peripheral devices are:

1. Making the USB device a master that controls the host PC, breaking thus dependency of final result on PC. As said, some new USB audio devices are supposedly deigned this way. Up to now their performance however hasn't been published.

2. Use of secondary PLL. General traditional method that is still not perfect but has good merits.

3. Use of asynchronous sample rate converter (ASRC). General modern way to remove the jitter, unfortunately rather than removes the jitter, it embeds it into the data.


Audial D/A converters and USB

The first version of the Audial D/A converter The Model has been using the PCM2706 as the USB decoding engine, with no further jitter reduction or galvanic isolation. The latest Audial DAC, AYA II, is using the same approach.

Feedback we've had up to now points out that in most cases it was the S/PDIF input that yielded superior performance. In some way this is surprising since the jitter associated to the PCM2706 decoder previously appeared to work well with TDA1541A (as said, a similar kind of jitter is produced by asynchronous reclocking which I've been using for a couple of years). Also, my original experiments with the USB interface, also based on the PCM2706 but with the TDA1543 D/A chip, brought performance that was at least equal to that of the good S/PDIF source. The main problem with the USB interface when used with the TDA1541A is about certain smearing, a kind of delta/sigma sonic signature. I am prone to associate such a problem rather to the sensitivity of TDA1541A to the noise coupling, than to the linked jitter.


Pedja Rogic, March 2008

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