Newsgroups: comp.speech
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From: yves@mars.dgrc.doc.ca (Yves Jolly)
Subject: Re: Lowpass? Filter?
Message-ID: <1992Dec4.144947.29569@clark.dgim.doc.ca>
Sender: news@clark.dgim.doc.ca (Usenet News)
Reply-To: yves@mars.dgrc.doc.ca
Organization: Communication Research Centre
References: <BypwuH.BuL@cs.dal.ca>
Date: Fri, 4 Dec 92 14:49:47 GMT
Lines:       26

In article BuL@cs.dal.ca, layes@ug.cs.dal.ca (Jonathan Layes) writes:
> In article <1flkdbINNh8e@agate.berkeley.edu> ksanthan@garnet.berkeley.edu (Kumaran Santhanam) writes:
> >I'm sorry, Thijs...I meant in software.  I want to know how to implement
> >the mathematics for a lowpass filter.  I have a stream of SoundBlaster Pro
> >data in 8-bit amplitude format.  I want to implement a lowpass for this.
> 
> Look in any standard text dealing with Fourier transforms, and to
> do the discrete Fourier transform in any realistic amount of time,
> look up a FFT algorithim.  All the necessary information should be
> there.  (there are lots of texts on the subject - I just presented
> a seminar on such stuff)
> 
> Jonathan
> 

I'm sorry guys, but you really confuse me.  First, Kumaran: what do you want to do; design the impulse response of a lowpass filter or implement a lowpass filter ? Two different things.  FIR or IIR ?  Any basic DSP book will give you that answer a lot easier than I can here.  Second, Jonathan: the use I see for FFTs in this discussion is to see the frequency response of your filter.  Yes, there are ways to implement filters using FFTs, but for a fixed simple lowpass, the discrete convolution is many, many 






times simpler.  If you think of using FFTs for the filter design, it is also possible, but again there are more efficient ways (Park-McClellan type of design).


---
Yves Jolly		Email:	yves@mars.dgrc.doc.ca
Communications Research Centre, Dept. of Communications
P.O. Box 11490, Stn. H, Ottawa, Ont., CANADA  K2H 8S2
Phone: (613) 998-2780		Fax: (613) 990-7987

