Decimation and Phase Shift

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2 total messages Started by Bill Smith Thu, 28 Sep 1989 13:40

#304

Author: Bill Smith
Date: Thu, 28 Sep 1989 13:40

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I have seen a few terms in comp.dsp recently that I am unfamiliar with.
Would someone be kind enough to mail me a definition?  I'll try to post
a summary if someone else hasn't beaten me to it.

The term that I am most unfamiliar with is "decimation."

Also, although phase shift is fairly clear what it means, I am curious
what a hi-fi system that had excessive phase shift would sound like.
Would if affect mainly sounds like a rim shot on a drum that are I could
imagine are similar to an impulse function and thus have a large high
freqency component?

Thanks.

Bill Smith
uunet!pur-ee!mdbs!wsmith

Re: Decimation and Phase Shift

#322

Author: Charlie Thompson
Date: Fri, 29 Sep 1989 18:34

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In article <1453@mdbs.UUCP>, wsmith@mdbs.UUCP (Bill Smith) writes:
> 
> I have seen a few terms in comp.dsp recently that I am unfamiliar with.
> Would someone be kind enough to mail me a definition?  I'll try to post
> a summary if someone else hasn't beaten me to it.
> 
> The term that I am most unfamiliar with is "decimation."
> 
> Bill Smith
> uunet!pur-ee!mdbs!wsmith

Folklore has it that decimation was first carried out by the Romans...
when they lined the people of a village up and killed every 10th person.
This, I guess, showed who was boss or something.

The term has come to mean the inclusion/deletion of every Nth item ( not
necessarily 10 ).  In the sampling process taking every Nth sample is
referred to as N:1 decimation.  This reduces the sample rate by a factor
of N.  This cannot, however, be done without regard to the spectral content
of the orginal signal and it's sample rate.  Usually the decimation 
process is preceded by a bandwidth reduction filter.  The bandwidth of
the original signal must be reduced or aliasing will occur due to the
decimation process. Many filters get called decimation filters...usually
they are just some form of lowpass filter to reduce the bandwidth.

This is sort of a simple explanation not meant for DSP textbooks.

-C.T.

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