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From: bradr@quorum.com (Brad Rubenstein)
Newsgroups: comp.dsp
Subject: trivial low pass filter question
Message-ID: <1991May5.211712.16328@quorum.com>
Date: 5 May 91 21:17:12 GMT
Organization: Quorum Software Systems, Inc.
Lines: 22

I'm sure someone out there can answer this off the top of his/her
head.  I'm trying to avoid going out and buying a reference book
for a one-time problem.

I have a signal sampled at rate f1, and I want to resample it at f2
(<f1) as efficiently as possible.  It appears, to prevent objectionable
aliasing, I have to band-limit the original signal to frequencies below
f2/2.

I was considering the quickest way to do the low pass filtering is to
let out[t] = (1-q)*in[t] + q*out[t-1].

What is the equation that relates the frequency response of this
function to the parameter q?  If I want to trade a few more multiplies
for a sharper cut off, what transfer function can I use?

Please respond via email to bradr@quorum.com.  Thanks mucho.

Brad Rubenstein

-- 
Brad Rubenstein	-- Quorum Software Systems, Inc. -- bradr@quorum.com