Subject: From:at <tothlINF.U-SZEGED.HU>Date:Tue, 22 Jun 1999 10:13:00 MET>From tothl Tue Jun 22 10:13:05 +0200 1999 remote from inf.u-szeged.hu Date: Tue, 22 Jun 1999 10:13:05 +0200 (MET DST) From: Toth Laszlo <tothl(at)inf.u-szeged.hu> X-Sender: tothl(at)csilla To: auditory(at)lists.mcgill.ca Subject: Re: Cepstrum computation In-Reply-To: <4.1.19990621105041.00a58450(at)ricochet.net> Message-ID: <Pine.SV4.3.91.990622100611.7290B-100000(at)csilla> MIME-Version: 1.0 Received: from inf.u-szeged.hu by inf.u-szeged.hu; Tue, 22 Jun 1999 10:13 MET Content-Type: TEXT/PLAIN; charset=US-ASCII Content-Length: 1102 On Mon, 21 Jun 1999, Richard F. Lyon wrote: > > C(t)=|| FFT( log( ||FFT(x)|| ) ) || > > > >My question is: what happens when ||FFT(x)||=0 for some x? > >Then we have to compute log(0), which is undefined (as we all know). > > > Yes, isn't it ridiculous that people sort of define things part way > and then pretend they're OK? > Yes, ridiculous indeed. A mathematician would definitely add a comment like "and if ||FFT(x)||=0 then ...". When I wrote my first cepstrum code it took me many hours to figure out why I get black lines in my images... My solution was an if: if(||FFT(x)||==0) { y=-BigNumber} else {y=log(||FFT(x)||) Where "BigNumber" is some big constant. Yes, it's terrible, but what could have I done? Laszlo Toth Hungarian Academy of Sciences * "Military intelligence: Research Group on Artificial Intelligence * two words combined that e-mail: tothl(at)inf.u-szeged.hu * can't make sense" http://www.inf.u-szeged.hu/~tothl *

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