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From: lou@caber.valid.com (Louis K. Scheffer)
Newsgroups: comp.dsp
Subject: Re: 48k to 44.1k sample rate conversion
Message-ID: <500@valid.valid.com>
Date: 27 May 91 00:49:36 GMT
References: <5826@media-lab.media.mit.edu.MEDIA.MIT.EDU> <1991May13.173129.18295@bernina.ethz.ch> <1991May15.105543.12165@bernina.ethz.ch> <1991May16.052920.21060@netcom.COM> <481@valid.valid.com> <4035@motcsd.csd.mot.com>
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lance@motcsd.csd.mot.com (lance.norskog) writes:

>Ok, now we're getting somewhere.  The SPUT sound operating system
>for DOS (shareware by Adrienne Cousins) has high-pass and low-pass
>filtration options for playing back sound samples.  SPUT is a DOS
>TSR (background program) comprising 5K of 8086 code, so we know
>it doesn't have 13,000 coefficients.

>If interpolation is being used for the low-pass operation, is it
>also being used for the high-pass problem?

I don't know this software, so I'm guessing.  It is probably not
interpolation, but a simple digital filter.  These work by taking
the last N samples, multiplying them by a bunch of constants
a[1],...,a[n] and adding the results.  You can (optionally) take
the computed output and use it in the computation on the next
sample as well.  You only need a few coefficients (maybe 10) to
get low-pass, high-pass, and bandpass responses, with responses
like analog audio equipment. The zillion coefficient case is only
when you are trying to do something tricky.

-Lou Scheffer