From shughes@rwth-aachen.de Thu May 18 06:45:44 1995
Path: ashpoly!cascade!transat!eunet-fi!relcom!kiae!rwth-aachen!shughes
From: shughes@rwth-aachen.de (Steve Hughes)
Newsgroups: comp.dsp
Subject: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier
Message-ID: <1995May18.064544.8104@rwth-aachen.de>
Date: Thu, 18 May 1995 06:45:44 GMT
Organization: RWTH Aachen Informatik
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Comparing window sidelobe attenuation on 16-bit 44.1 kHz WAV files.

At 14.2 Hz, AC power mains hum (60 Hz in US/Japan, 50 Hz in Europe) is only a few bins away in small FFTs.
A Kaiser-Bessel window with parameter beta = 8.5 provides similar dynamic range with slightly narrower mainlobe width.

MATLAB script available upon request via email.

-- 
Steve Hughes -- RWTH Aachen Informatik
"Hardware is temporary. The signal survives."

From ksmirnov@uu.net Thu May 18 16:12:44 1995
Path: ashpoly!cascade!bigsur!uu!ksmirnov
From: ksmirnov@uu.net (Katrin Smirnov)
Newsgroups: comp.dsp
Subject: Re: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier
Message-ID: <1995May18.161244.8593@uu.net>
Date: Thu, 18 May 1995 16:12:44 GMT
References: <1995May18.064544.8104@rwth-aachen.de>
Organization: UUNET Technologies, Falls Church VA
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In article <1995May18.064544.8104@rwth-aachen.de>, shughes@rwth-aachen.de (Steve Hughes) writes:
> Comparing window sidelobe attenuation on 16-bit 44.1 kHz WAV files.
> At 14.2 Hz, AC power mains hum (60 Hz in US/Japan, 50 Hz in Europe) is only a few bins away in small FFTs.

Don't forget that if you downsample to 64 Hz first, your FFT resolution jumps to 0.015 Hz per bin with a modest 4096-point transform.

-- 
Katrin Smirnov
Opinions expressed are solely my own and not those of UUNET Technologies, Falls Church VA.
------------------------------------------------------------

From sstewart@rwth-aachen.de Fri May 19 06:35:44 1995
Path: ashpoly!cascade!transat!ukc!fennimore!rwth-aachen!sstewart
From: sstewart@rwth-aachen.de (Steve Stewart)
Newsgroups: comp.dsp
Subject: Re: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier
Message-ID: <1995May19.063544.3014@rwth-aachen.de>
Date: Fri, 19 May 1995 06:35:44 GMT
References: <1995May18.064544.8104@rwth-aachen.de> <1995May18.161244.8593@uu.net>
Organization: RWTH Aachen Informatik
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In article <1995May18.161244.8593@uu.net>, ksmirnov@uu.net (Katrin Smirnov) writes:
> Don't forget that if you downsample to 64 Hz first, your FFT resolution jumps to 0.015 Hz per bin with a modest 4096-point transform.

Excellent advice on the Blackman-Harris window. Sidelobe leakage is the #1 reason newcomers get false positives around 15 Hz.

-- 
=== Steve Stewart ===
Dept of Electrical Engineering, RWTH Aachen Informatik
"There are 14 nodes and only 10 countries. Count again."

From lmartinez@illinois.edu Fri May 19 12:29:44 1995
Path: ashpoly!cascade!bigsur!illinois!lmartinez
From: lmartinez@illinois.edu (Lars Martínez)
Newsgroups: comp.dsp
Subject: Re: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier
Message-ID: <1995May19.122944.1160@illinois.edu>
Date: Fri, 19 May 1995 12:29:44 GMT
References: <1995May18.064544.8104@rwth-aachen.de>
Organization: University of Illinois Urbana-Champaign
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In article <1995May18.064544.8104@rwth-aachen.de>, shughes@rwth-aachen.de (Steve Hughes) writes:
> Comparing window sidelobe attenuation on 16-bit 44.1 kHz WAV files.
> At 14.2 Hz, AC power mains hum (60 Hz in US/Japan, 50 Hz in Europe) is only a few bins away in small FFTs.

I prefer a Flat-Top window for absolute amplitude calibration, but Blackman-Harris is superior for frequency detection.

-- 
Lars Martínez <lmartinez@illinois.edu>
Zyxel U-1496E @ 19,200 bps
"The carrier frequency does not drift by accident."