Thread: Band-pass filter

Started: 2017-09-20 22:08:15
Last activity: 2017-09-21 19:15:12
Topics: SAC Help
Rehman .
2017-09-20 22:08:15
Hello,
I have band passed a teleseismic event waveform with ( bp c
0.01 0.1 n 4 p 2), It filtered the noise and given a nice waveform shape.
But buy applying multiple times band-pass filter ( bp c 0.01 0.1 n 4 p 2)
to same waveform I observed slight change in waveform every time. Why it is
so? Can I work with multiple times filtered waveform?

  • Milton Plasencia
    2017-09-21 19:15:12
    Hi Rehman,

    I do not understand because you applied a filter repeatedly, anyway.

    I attach a plot when is applied your filter four times to an impulse,
    sac command: sac> funcgen.

    Obviously the results that the filter modify slightly the amplitude of
    signal and also a delay (time axe)
    in each instance.

    In sac I do:

    SAC> funcgen

    SAC> bp c 0.01 .1 n 4 p 2

    SAC> w 1.sac

    SAC> bp c 0.01 .1 n 4 p 2

    SAC> w 2.sac

    SAC> bp c 0.01 .1 n 4 p 2

    SAC> w 3.sac

    SAC> bp c 0.01 .1 n 4 p 2

    SAC> w 4.sac

    SAC> p2

    SAC> r ./1.sac ./2.sac ./3.sac ./4.sac

    SAC> p2

    SAC> color on inc

    SAC> p2

    Cheers,

    Milton






    ************************************
    Milton P. PLASENCIA LINARES

    Centro di Ricerche Sismologiche (CRS)
    OGS - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale

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    ASAIN (Antarctic Seismographic Argentinean Italian Network)
    *********************************

    On 20 September 2017 at 17:05, Rehman . <rehman.techgeophy<at>gmail.com> wrote:

    Hello,
    I have band passed a teleseismic event waveform with ( bp c
    0.01 0.1 n 4 p 2), It filtered the noise and given a nice waveform shape.
    But buy applying multiple times band-pass filter ( bp c 0.01 0.1 n 4 p 2)
    to same waveform I observed slight change in waveform every time. Why it is
    so? Can I work with multiple times filtered waveform?


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05:14:18 v.b4412d20