Subject: [linux-audio-dev] Syncronizing Sample Clocks [WAS: A bit of goodnews--paper now available for your viewing pleasure and/or comments]
From: Fred Gleason (fredg_AT_salemradiolabs.com)
Date: Fri May 28 2004 - 22:49:08 EEST
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! |
| The answer is twelve? I think I'm in the wrong building. |
| -- Charles Schulz |
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