PSN-L Email List Message

Subject: Re: Modulated Seismic
From: Mike Price mprice@........
Date: Sat, 23 Apr 2011 03:05:41 -0700


One technique if the Goertzel Filter. Conceptually, it is a single bin 
DFT. It's easy to code and very efficient. One common use is DTMF tone 
detection, since it can be implemented on simple processors.

A summary of the algorithm and some code can be found at: 
http://www.mstarlabs.com/dsp/goertzel/goertzel.html

Mike

On 4/22/2011 8:16 PM, Geoffrey wrote:
> Is there some way to pick a frequency
> like 0.123 Hz then process the sampled
> seismic signal to see if any energy of only
> that frequency is present ?
>
> Can you point me to a complete subroutine
> [complete meaning does not use a library of functions]
> to obtain such an answer ?
>
> It would be like an FFT but you give the data,
> sample rate, and what SINGLE freq to look for ?
>
>
> -----Original Message----- From: Chuck / Judy Burch Sent: Sunday, April
> 17, 2011 3:44 PM To: psnlist@.............. Subject: Modulated Seismic
>
> All,
>
> Thanks to Randal for raising this interesting topic. The Teager-Kaiser
> Algorithm and Randal's rectification scheme are efforts to find the
> instantaneous amplitude (or envelop) of a seismic record. Think of a
> short enough piece of a seismic record -- it can be modeled by a
> waveform of a given frequency, phase and amplitude. Throw away the
> frequency and phase information and you are left with just the amplitude
> as a function of time. So you can think of a record (very approximately)
> as a collection of unit-amplitude waveforms from an appropriate
> frequency range that has been AM modulated by the envelop.
>
> The FFT of the envelop, then, can be thought of as the Fourier Transform
> of the "modulating" function.
>
> There are different ways of approximating the envelop. Many texts on
> signal processing discuss the "analytic trace" or "analytic signal"
> method, which is mathematically rigorous. If the original record is X,
> then the quadrature (90 degree advanced) record, Y, is the Hilbert
> Transform of X. The envelop of X is SQRT ( X2 + Y2 ).
>
> In the (remote) chance that anyone wants to pursue this, contact me and
> I'll show you an easy way to calculate the Hilbert Transform.
>
>
> Chuck Burch
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