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From: cdc@uafhcx.uucp (C. D. Covington)
Newsgroups: comp.dsp
Subject: Re: Combining samples......
Summary: multirate dsp problem
Message-ID: <4697@uafhp.uark.edu>
Date: 1 Jun 90 15:46:56 GMT
References: <1990May28.112524.4264@lth.se> <4375@ge-dab.GE.COM>
Sender: netnews@uafhp.uark.edu
Organization: College of Engineering, University of Arkansas, Fayetteville
Lines: 29


In article <4375@ge-dab.GE.COM>, harrison@sunwhere.DAB.GE.COM (Gregory Harrison) writes:
> In article <1990May28.112524.4264@lth.se> d88pt@efd.lth.se (Peter Tomaszewski) writes:
> >Hi,
> >
> >
> >I would like to know how you combine two samples. If they are sampled at the
> I suppose you could just interpolate one of the samples to have it's
> datapoint be time-aligned with the other sample.  You could use the 
> spline function in Matlab for instance, or just write a little
> interpolator.  You would use time as the independant variable.
> 
> Greg Harrison 
> GE

    I cannot tell if my previous posting went out yesterday.  We have had
disk full problems on our netnews server.  Interpolation is the correct
answer to get the inbetween samples.  The ideal interpolation pulse is
the sinc function  sin(pi*x)/(pi*x) as predicted by Nyquists sampling theorem
where the signal must be lowpass to avoid aliasing.  In fact the sinc pulse
is an ideal lowpass filter in the frequency domain - amazing.

    I did do an analysis of optimum truncated (time-limited) interpolation
functions and was led to the prolate spheroidal wave function set.  These
functions have optimum lowpass characteristics for a given time limitation.
If the time limitation is relaxed, we revert to the sinc pulse solution.

C. David Covington (WA5TGF)  cdc@uafhcx.uark.edu     (501) 575-6583
Asst Prof, Elec Eng          Univ of Arkansas        Fayetteville, AR 72701