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Date: Sat, 09 Jan 1999 16:09:55 +0000
From: James Gregory <pgregory@thepla.net>
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To: alsa-user@alsa.jcu.cz
Subject: Re: 4 soundcards on a same machine and future of Multitrack
References: <001701be3a16$2082ff20$47010180@pcbg>
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You have to do clock synching to prevent the tracks from going out of tune.
Slight variations in the quartz crystals which regulate the sound cards
operation will mean that if you plan to mix down or play through one of the
cards, you will get some tracks sounding out of tune, because some might
record at 44001hz or 43999 hz, this will cumulate to sound horrible, also,
eventually you will hear the rhythm going out. Alternatively you could only
play the tracks on the device they were recorded on and mix them with analog
technology. (ie a REAL mixer). I will be intrigued if you can get multi-track
to run on ALSA, I would like to do this also. I don't know if ALSA supports
them, but there are some cards around for a few hundred dollars which allow
you to do multiple ins and outs on the one card, which means you don't have to
do synching. KORG have one, although it is quite expensive, I think the
cheapest Event Electronics card would be what you are after (don't know the
name), but like I said, check compatability. The other thought I had would be
to introduce some form of clock synching in the software, eg modify the
source, such that it checks how many samples have been taken up to a point
measured by the real time clock on the computer, and then perform a time
expand/contract transform on the sample to compensate for any synching
problems between tracks... Just an idea, it would have to be done after the
track had been recorded, because it would add a huge CPU overload,
unfortunately, I haven't started uni yet, so I can't help you with that,
anyways, must go, good luck, let us know how you get on.

Regards,

Jim.

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 ?
>
> I understand we have to synchronize video cards or frame grabbers but why
> synchronizing
> audio cards ? Can't we just see them as separate 'recorders' ?
>
> I ask you this because this set up (3 or 4 AudioPCI) interests me a lot...
>
> (AudioPCI are cheap and high S/N ratio so -> cheap multitrack)
>
> Benjamin GOLINVAUX.
>
> :
> :+---- --- -- -  -   -    -
> :|Frank van de Pol                  -o)
> :|Frank@vande-pol.demon.nl          /\\
> :|                                 _\_v
> :|Linux - Why use Windows, since there is a door?
> :|
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