From alsa-user-owner@alsa.jcu.cz  Thu Jan  7 19:58:26 1999
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	Thu, 7 Jan 1999 19:56:51 +0100
Date: Thu, 7 Jan 1999 19:56:51 +0100 (CET)
From: Jaroslav Kysela <perex@jcu.cz>
To: Monty <xiphmont@mit.edu>
cc: alsa-user@alsa.jcu.cz
Subject: Re: 4 soundcards on a same machine and future of Multitrack 
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On Thu, 7 Jan 1999, Monty wrote:

> 
> >:Perhaps the SB PCI64 (Ensoniq audiopci / ES1370) cards are interesting for
> >:you? These are PCI boards don't use ISA DMA, and have in addition 2 stereo
> >:outputs. (ie. 2 in / 4 out). You'll still need some hardware modification
> >:to sync the clocks.
> >:
> >:Frank.
> >
> >Please, could you explain why we have to synchronize the clocks ?
> 
> Because clocks drift.  The cheap clocks used in most computers and
> sound cards will typically wander and drift several percent.  If you
> record tracks on two different soundcards with a clock difference of
> .5%, 10 minutes of audio will be out of sync three seconds at the end.

Note that synchronization code should be in application code for ALSA
driver which allows measure record start time and time in which will
arrive next sample from kernel side ring buffer.

This will allow to application start all record streams by independent
ways and do some rate conversions plus sample skipping (to synchronize
start of record stream). I know - this will be hard for coding, but
useable without buying some special hardware or hacking kernel-side
drivers.

							Jaroslav

-----
Jaroslav Kysela <perex@jcu.cz>
Academic Computer Centre, University of South Bohemia
Branisovska 31, C. Budejovice, CZ-370 05 Czech Republic


