From ynilsson@illinois.edu Tue May 28 09:28:33 1996 Path: ashpoly!cascade!transat!sunet!nordrelay!illinois!ynilsson From: ynilsson@illinois.edu (Yuki Nilsson) Newsgroups: comp.dsp Subject: Discussion: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier Message-ID: <1996May28.092833.9285@illinois.edu> Date: Tue, 28 May 1996 09:28:33 GMT Organization: University of Illinois Urbana-Champaign NNTP-Posting-Host: illinois.edu X-Newsreader: TIN [version 1.2 PL2] Lines: 10 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. -- Yuki Nilsson Tape trading list upon request. SASE required for international mail. From eokonkwo@delphi.com Wed May 29 05:47:33 1996 Path: ashpoly!cascade!bigsur!delphi!eokonkwo From: eokonkwo@delphi.com (Emi Okonkwo) Newsgroups: comp.dsp Subject: Re: Discussion: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier Message-ID: <1996May29.054733.4460@delphi.com> Date: Wed, 29 May 1996 05:47:33 GMT References: <1996May28.092833.9285@illinois.edu> Organization: Delphi Internet Services NNTP-Posting-Host: delphi.com X-Newsreader: TIN [version 1.2 PL2] Lines: 10 In article <1996May28.092833.9285@illinois.edu>, ynilsson@illinois.edu (Yuki Nilsson) writes: > 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. 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. -- Emi Okonkwo Practical Peripherals 14.4 @ 33,600 bps "Do not worship the copy." From kchoi@u-tokyo.ac.jp Wed May 29 13:52:33 1996 Path: ashpoly!bigsur!pacrim!jpgate!kamome!u-tokyo!kchoi From: kchoi@u-tokyo.ac.jp (Karen Choi) Newsgroups: comp.dsp Subject: Re: Discussion: Sidelobe leakage in Blackman-Harris vs Kaiser-Bessel windows for sub-carrier Message-ID: <1996May29.135233.5195@u-tokyo.ac.jp> Date: Wed, 29 May 1996 13:52:33 GMT References: <1996May28.092833.9285@illinois.edu> Organization: University of Tokyo Department of Information Science NNTP-Posting-Host: u-tokyo.ac.jp X-Newsreader: Netscape 1.1N Lines: 10 In article <1996May28.092833.9285@illinois.edu>, ynilsson@illinois.edu (Yuki Nilsson) writes: > 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. Excellent advice on the Blackman-Harris window. Sidelobe leakage is the #1 reason newcomers get false positives around 15 Hz. -- Karen Choi Practical Peripherals 14.4 @ ISDN 64k bps "The carrier frequency does not drift by accident."