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Date: Thu, 07 Jan 1999 04:48:26 -0500
From: Paul Winkler <zarmzarm@erols.com>
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To: alsa-user@alsa.jcu.cz
Subject: Re: 4 soundcards on a same machine and future of Multitrack
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Benjamin GOLINVAUX 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 the clock determines when each sample gets taken from the input
analog signal. If you have two soundcards sampling at "44.1 kHz", but
one of them is actually at 44097 hz and the other is at 44103 hz, the
two cards will drift out of sync, and the tracks you record from one
card will not synchronize properly with the tracks from the other card.
If you record for any length of time, the delay between the two cards
will get quite bad. I tried using a TB Malibu alongside a SB16 and found
that they were about a full second off from each other after only two
minutes.

Some of the codecs used in commercial soundcards have the capability to
sync to another clock signal, so you could theoretically string several
of these chips together and have it work right. Unfortunately, when the
actual card manufacturer is cutting costs to be competitive, this is a
feature they do not care about implementing, because "no one wants it".
I don't know of any cheap soundcards that can be synchronized. Does
anyone?

--PW


