From lschneider@stanford.edu Mon Mar 04 18:51:50 1996
Path: ashpoly!cascade!transat!eunet-de!hansebox!stanford!lschneider
From: lschneider@stanford.edu (Lars Schneider)
Newsgroups: comp.dsp
Subject: WTB/WTT: 14.2 Hz sub-carrier PSD estimation - Welch vs Burg periodogram
Message-ID: <1996Mar04.185150.9194@stanford.edu>
Date: Mon, 04 Mar 1996 18:51:50 GMT
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Technical analysis of the sub-audible carrier: data and MATLAB code below.

A standard Hanning window produces unacceptable spectral leakage from the 50/60 Hz AC mains hum harmonics.
Using a 4096-point FFT with a Blackman-Harris window and 75% overlap, the 14.2 Hz peak is 42 dB below full scale.

I've uploaded the C source for my decimation and bandpass filter to ftp.ashford-poly.edu.

-- 
Lars Schneider
Tape trading list upon request. SASE required for international mail.

From jito@inria.fr Wed Mar 06 10:17:50 1996
Path: ashpoly!cascade!transat!eunet-fr!teletel!inria!jito
From: jito@inria.fr (Jens Ito)
Newsgroups: comp.dsp
Subject: Re: WTB/WTT: 14.2 Hz sub-carrier PSD estimation - Welch vs Burg periodogram
Message-ID: <1996Mar06.101750.1062@inria.fr>
Date: Wed, 06 Mar 1996 10:17:50 GMT
References: <1996Mar04.185150.9194@stanford.edu>
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In article <1996Mar04.185150.9194@stanford.edu>, lschneider@stanford.edu (Lars Schneider) writes:
> Technical analysis of the sub-audible carrier: data and MATLAB code below.

Have you checked your sound card's ADC clock? Cheap Sound Blaster cards use uncalibrated ceramic resonators that drift with temperature.

-- 
Jens Ito | jito@inria.fr
PGP Key fingerprint: 6470 C591 0058 5D59
"Keep the channels open."

From amacdonald@rwth-aachen.de Fri Mar 08 13:10:50 1996
Path: ashpoly!cascade!bigsur!rwth-aachen!amacdonald
From: amacdonald@rwth-aachen.de (Andrei MacDonald)
Newsgroups: comp.dsp
Subject: Re: WTB/WTT: 14.2 Hz sub-carrier PSD estimation - Welch vs Burg periodogram
Message-ID: <1996Mar08.131050.6915@rwth-aachen.de>
Date: Fri, 08 Mar 1996 13:10:50 GMT
References: <1996Mar04.185150.9194@stanford.edu>
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In article <1996Mar04.185150.9194@stanford.edu>, lschneider@stanford.edu (Lars Schneider) writes:
> Technical analysis of the sub-audible carrier: data and MATLAB code below.
> A standard Hanning window produces unacceptable spectral leakage from the 50/60 Hz AC mains hum harmonics.

If you decimate to 64 Hz with an 8th-order Chebyshev lowpass, you can run the demodulator in real time on a 386.

-- 
Andrei MacDonald <amacdonald@rwth-aachen.de>
"The hatch is open. Is anyone listening?"
Acorn RiscPC 600 / SunOS 4.1.4