[linux-audio-dev] Syncronizing Sample Clocks [WAS: A bit of goodnews--paper now available for your viewing pleasure and/or comments]

[Fred Gleason]

On Friday 28 May 2004 15:19, Ivica Ico Bukvic wrote:
> Hmm, it would be a fun project then to come up with a profiler of various
> audio cards by recording and then capturing a specific buffer of audio
> data. Then by comparing them (assuming that this drift is constant) see how
> many empty samples there are (or if the playback is slower, how many
> samples are missing), and then create a framework that allows real-time
> resampling in order to compensate for that discrepancy whenever multiple
> soundcards are being used :-D

I strongly suspect that you'd find your results to be non-repeatable.  Many 
factors can subtly influence the output frequency of even crystal-locked 
SRGs: ambient temperature, power supply voltage variation, even component 
aging.

This issue affects many more applications than just audio.  *Any* system that 
requires precise replication of clock (as, for example, most any digital 
telecommunication scheme does) faces this dilemma.  In the end, some form 
*locking*, slave clock to master, is needed.  A variety of methodologies, 
such as PLL (phase lock loop) exist to do this, but the bottom line remains 
that some sort of hardware support will be necessary.

Cheers!


|-------------------------------------------------------------------------|
| Frederick F. Gleason, Jr. | Director of Broadcast Software Development  |
|                           |             Salem Radio Labs                |
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|  I know the answer!  The answer lies within the heart of all mankind!   |
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