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From: dan@chaos.cs.brandeis.edu (Dan Schwarz)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Limitations in recording and playback of digitized audio.
Keywords: audio processing bottlenecks
Message-ID: <1990Oct13.165359.14653@chaos.cs.brandeis.edu>
Date: 13 Oct 90 16:53:59 GMT
References: <2332@wroach.cactus.org>
Organization: Brandeis University Computer Science Dept
Lines: 53

In article <2332@wroach.cactus.org> mk@wroach.cactus.org (M. Khan) writes:
>Is there a hardware bottleneck that prevents digitized audio to
>be recorded concurrently to disk, or played back similarly,
>without interruption of the audio?
>
>What models of the Mac have this bottleneck?
>
>If there is no such (or on models that have no such)
>bottleneck does software that provides "virtual memory"
>(don't remember any names now) work to get around
>the limitations of audio-digitizing software that limits
>itself to available memory?  Any experiences with this?
>
>Also, in case there is no bottleneck, are there any software
>packages that work with a MacRecorder that dont limit you
>to available memory?

The Macintosh has no inherent bottlenecks which prevent it from recording
direct-to-disk or playing back direct-from-disk. Certainly the machines
equipped with Apple Sound Chips have the potential to do it; machines
with the Sony Sound Chip (Mac Portable, Mac SE and earlier) may be limited
to the 22khz sampling rate when doing simultaneous disk operations.
(When you say "disk" I assume you mean hard disk, not floppy or fileserver.)

All you need is some clever software... which, as far as I know, does not
exist yet. But it CAN be done, and WILL be done. Articulate Systems Inc.'s
VOICE LINK(tm) digitizer product will eventually include software with this
capability. For more information, write and ask for product literature.

As far as using virtual memory to simulate RAM for the purposes of recording,
I think you'll find the results to be unsatisfactory. You'll get glitches
when the disk is accessed. This is especially true with polled recording
devices like the MacRecorder(tm) which chew up large amounts of CPU time to
do their work. Notice that you can't even move the mouse when recording with
the MacRecorder - disk access is far more disruptive. The Voice Link is
interrupt driven, so it will eventually be able to record to disk.

Playback from virtual RAM may work okay, depending on the scheme that is used
to play sounds. Asynchronous playback with good buffering systems would do
fairly well with a VRAM system.

Disclaimer: I work for Articulate Systems Inc. and have been involved in the
development of the Voice Link and other products. This is not intended to
be a product endorsement... (although I certainly wouldn't mind if you bought
one..:-)

_Dan

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