Thread: fft amplitude

Started: 2019-02-06 23:10:49
Last activity: 2019-02-07 16:31:30
Topics: SAC Help
Mar Tapia
2019-02-06 23:10:49
Hi to all,

I would like to know if the fft amplitude (fft; keepam) in sac is the
module of fourier transform (amplitude*s) or is the power of amplitude
(amplitude*s)^2

Thanks,

Mar

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Mar Tapia

mar.tapia<at>gmail.com
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  • George Helffrich
    2019-02-07 16:31:30
    Dear All -

    Try this experiment with SAC:

    fg sine 1 0 npts 4096 delta 0.01; mul 1; div (40.96 / 2); fft amph; psp am

    (The div command compensates for the (N*Delta/2) normalization for the FFT.) The plot shows the peak amplitude is one (at 1 Hz). If you change the “mul 1” to “mul 2” the amplitude peak becomes 2. Hence, the amplitude is true amplitude, not power.

    On 6 Feb 2019, at 23:11, Mar Tapia <mar.tapia<at>gmail.com> wrote:

    Hi to all,

    I would like to know if the fft amplitude (fft; keepam) in sac is the module of fourier transform (amplitude*s) or is the power of amplitude (amplitude*s)^2

    Thanks,

    Mar

    --
    -----------------------------------------------------------
    Mar Tapia

    mar.tapia<at>gmail.com <mar.tapia<at>gmail.com>
    ------------------------------------------------------------

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    George Helffrich
    george<at>elsi.jp


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