Subject: Re: [linux-audio-dev] hdr disk throughput
From: David Olofson (david_AT_gardena.net)
Date: Fri Mar 17 2000 - 22:09:05 EST
On Fri, 17 Mar 2000, Benno Senoner wrote:
> > Changing the disk sample size from 32 to 24 bits will have very little
> > effect on the seeking that is needed. And besides, 32 bit sample data
> > can't be very far away right now. So why not design for it?
> >
>
> little effect on the seeking but 25% on disk i/o transfer,
> it's a combination of both.
> I can't give you exact numbers but I suspect around 15%.
This seems reasonable, looking at the difference between Cakewalk
(properly configured - not the ridicoulus 64-128 kB/track
buffers recommended...) using 24(32) bit files and 16 bit files.
IIRC, I got around 24 tracks with 32 bit files on this machine,
while it can handle 32 16 bih tracks. I should add that Cakewalk
doesn't exactly have the fastest engine around, so the CPU load for
mixing may be involved here as well.
Note that you have to take in account that while less bits lowers
the bandwidth requirement, it also means smaller buffers (more
seeing) AND (provided you're benchmarking ;-) more tracks.
> Anyway I agree: designing for 32bit isn't a bad idea,
> with your approach you get 32bit sample support for free.
And if you want more tracks without buying faster disks, you could
look into dynamic 16 bit data or something. (Basically floats with 16
bit "mantissa" and a common exponent for a few samples.) This,
however, does not result in a file format that's easy to deal with
in all situations... (You could store the exponents/level data
somewhere else, but then the audio files would still be brutally
compressed .wav files, at the best.)
//David
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