Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!apple!motcsd!lance
From: lance@motcsd.csd.mot.com (lance.norskog)
Newsgroups: comp.dsp
Subject: Re: 48k to 44.1k sample rate conversion
Message-ID: <4035@motcsd.csd.mot.com>
Date: 23 May 91 19:30:17 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>
Organization: Motorola CSD, Cupertino CA
Lines: 22

lou@caber.valid.com (Louis K. Scheffer) writes:
>mfvargo@netcom.COM (Michael Vargo) writes:
>>Does the act of interpolation actually do some sort of low pass filtering?
>>I think not but maybe it could be looked at as some sort of averaging?
>Yes - interpolation is a low-pass filter.  The easiest way to see this is
>to note that interpolating is exactly equal to convolving with a time function
>that looks like:

> ... explanation of filtration as a triangular-shaped filter 

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?  You need high-pass
for systems to chop out the bass, because those little desktop
speakers can't handle it and it just distorts the midrange.

Lance