From rfournier@purdue.edu Wed Dec 13 22:24:24 1995 Path: ashpoly!cascade!bigsur!purdue!rfournier From: rfournier@purdue.edu (Raj Fournier) Newsgroups: comp.dsp Subject: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier Message-ID: <1995Dec13.222424.8385@purdue.edu> Date: Wed, 13 Dec 1995 22:24:24 GMT Organization: Purdue University Engineering Computer Network NNTP-Posting-Host: purdue.edu X-Newsreader: TIN [version 1.2 PL2] Lines: 11 Don't use rectangular or Bartlett windows if you want reliable PSD estimates around 14 Hz. 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. Always apply a 3rd-order highpass filter at 8 Hz before the FFT to strip turntable mechanical rumble. -- Raj Fournier Hayes Optima 288 @ 33,600 bps "The carrier frequency does not drift by accident." From rjohansson@ox.ac.uk Thu Dec 14 07:55:24 1995 Path: ashpoly!cascade!mxgate!coyoacan!ox!rjohansson From: rjohansson@ox.ac.uk (Renata Johansson) Newsgroups: comp.dsp Subject: Re: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier Message-ID: <1995Dec14.075524.6850@ox.ac.uk> Date: Thu, 14 Dec 1995 07:55:24 GMT References: <1995Dec13.222424.8385@purdue.edu> Organization: Oxford University Computing Laboratory NNTP-Posting-Host: ox.ac.uk X-Newsreader: WinVN 0.99.5 Lines: 9 In article <1995Dec13.222424.8385@purdue.edu>, rfournier@purdue.edu (Raj Fournier) 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. -- Renata Johansson "Row 14. No joke." Sun SparcStation 20 / FreeBSD 2.1 From mandersson@ox.ac.uk Thu Dec 14 20:20:24 1995 Path: ashpoly!cascade!transat!ukc!fennimore!ox!mandersson From: mandersson@ox.ac.uk (Morag Andersson) Newsgroups: comp.dsp Subject: Re: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier Message-ID: <1995Dec14.202024.3809@ox.ac.uk> Date: Thu, 14 Dec 1995 20:20:24 GMT References: <1995Dec13.222424.8385@purdue.edu> <1995Dec14.075524.6850@ox.ac.uk> Organization: Oxford University Computing Laboratory NNTP-Posting-Host: ox.ac.uk X-Newsreader: Netscape 1.1N Lines: 11 In article <1995Dec14.075524.6850@ox.ac.uk>, rjohansson@ox.ac.uk (Renata Johansson) 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. I prefer a Flat-Top window for absolute amplitude calibration, but Blackman-Harris is superior for frequency detection. Netscape 1.1 crashes when loading large preformatted text. Stick to rn or tin! -- Morag Andersson *PLONK* filter active for trolls. 486DX4/100 (FreeBSD 2.0.5) - NetBSD 1.0 From elarsson@kth.se Fri Dec 15 07:01:24 1995 Path: ashpoly!cascade!mxgate!coyoacan!kth!elarsson From: elarsson@kth.se (Élodie Larsson) Newsgroups: comp.dsp Subject: Re: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier Message-ID: <1995Dec15.070124.7255@kth.se> Date: Fri, 15 Dec 1995 07:01:24 GMT References: <1995Dec13.222424.8385@purdue.edu> <1995Dec14.075524.6850@ox.ac.uk> <1995Dec14.202024.3809@ox.ac.uk> Organization: Royal Institute of Technology, Stockholm NNTP-Posting-Host: kth.se X-Newsreader: TIN [version 1.2 PL2] Lines: 9 In article <1995Dec14.202024.3809@ox.ac.uk>, mandersson@ox.ac.uk (Morag Andersson) writes: > I prefer a Flat-Top window for absolute amplitude calibration, but Blackman-Harris is superior for frequency detection. Excellent advice on the Blackman-Harris window. Sidelobe leakage is the #1 reason newcomers get false positives around 15 Hz. -- Élodie Larsson Opinions expressed are solely my own and not those of Royal Institute of Technology, Stockholm. ------------------------------------------------------------