Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!zephyr.ens.tek.com!tekfdi!videovax!bill
From: bill@videovax.tv.tek.com (William K. McFadden)
Newsgroups: comp.dsp
Subject: Re: Digital Filter Design package (including group delay)
Message-ID: <5709@videovax.tv.tek.com>
Date: 9 Feb 90 19:10:14 GMT
References: <3274@taux01.UUCP>
Reply-To: bill@videovax.tv.tek.com (William K. McFadden)
Organization: Tektronix TV Measurement Systems, Beaverton OR
Lines: 24
Keywords: DSP, Filter design, group delay

In article <3274@taux01.UUCP> cdaata%taux01.nsc.com@nsc.nsc.com writes:
>I am looking for a digital filter design package which allows the
>user to specify the filter's group delay. I'd appreciate if someone
>could point me to such software if it exists.

Actually, they all do, in a sense.  If you implement a linear phase FIR filter
by direct convolution, the group delay will be I for a filter with 2I+1 taps.
Hence, if you want a group delay of 50 samples, then the filter should have 101
taps.  Every filter design program I've seen lets you specify the number of
taps.

You can convert the group delay to seconds by dividing by the sample rate.  For
example, with a 50 KHz sampling rate, a group delay of 50 samples would be
1 mS.

In an IIR flter, the group delay is nonlinear.  In this case you would only be
able to specify its value at a single frequency.  I don't know of any filter
design packages that do this, although many will plot group delay vs.
frequency.
-- 
Bill McFadden    Tektronix, Inc.  P.O. Box 500  MS 58-639  Beaverton, OR  97077
bill@videovax.tv.tek.com,     {hplabs,uw-beaver,decvax}!tektronix!videovax!bill
Phone: (503) 627-6920       "The biggest difference between developing a missle
component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI