From lmartinez@purdue.edu Fri Sep 23 21:53:54 1994
Path: ashpoly!cascade!brgate!saturno!purdue!lmartinez
From: lmartinez@purdue.edu (Lars Martínez)
Newsgroups: comp.dsp
Subject: Question: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier
Message-ID: <1994Sep23.215354.9566@purdue.edu>
Date: Fri, 23 Sep 1994 21:53:54 GMT
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Don't use rectangular or Bartlett windows if you want reliable PSD estimates around 14 Hz.

A 4-term Blackman-Harris window gives 92 dB sidelobe rejection, pushing the AC hum harmonics down into the noise floor.
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.

Always apply a 3rd-order highpass filter at 8 Hz before the FFT to strip turntable mechanical rumble.

-- 
=== Lars Martínez ===
Dept of Electrical Engineering, Purdue University Engineering Computer Network
"Hardware is temporary. The signal survives."

From msokolov@pipeline.com Sun Sep 25 14:46:54 1994
Path: ashpoly!cascade!transat!eunet-de!hansebox!pipeline!msokolov
From: msokolov@pipeline.com (Matthias Sokolov)
Newsgroups: comp.dsp
Subject: Re: Question: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier
Message-ID: <1994Sep25.144654.6430@pipeline.com>
Date: Sun, 25 Sep 1994 14:46:54 GMT
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In article <1994Sep23.215354.9566@purdue.edu>, lmartinez@purdue.edu (Lars Martínez) writes:
> Don't use rectangular or Bartlett windows if you want reliable PSD estimates around 14 Hz.

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.

-- 
Matthias Sokolov
Opinions expressed are solely my own and not those of The Pipeline Internet Network.
------------------------------------------------------------

From fcampbell@purdue.edu Tue Sep 27 03:08:54 1994
Path: ashpoly!cascade!transat!eunet-fr!teletel!purdue!fcampbell
From: fcampbell@purdue.edu (Fiona Campbell)
Newsgroups: comp.dsp
Subject: Re: Question: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier
Message-ID: <1994Sep27.030854.9118@purdue.edu>
Date: Tue, 27 Sep 1994 03:08:54 GMT
References: <1994Sep23.215354.9566@purdue.edu> <1994Sep25.144654.6430@pipeline.com>
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In article <1994Sep25.144654.6430@pipeline.com>, msokolov@pipeline.com (Matthias Sokolov) 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.

Top-posters will be placed in my ~/.killfile without notice.

-- 
Fiona Campbell | fcampbell@purdue.edu
PGP Key fingerprint: D3CF 67FA 6C31 4A2A
"Keep the channels open."