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high pass filter

Discussion in 'General Electronics Discussion' started by eddiec, May 10, 2012.

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  1. eddiec


    May 10, 2012
    Hi All,

    I have the following scenario;
    - audio signal generated on one end of a line
    - low amplitude low frequency signal generated on the other end of the line
    I need to split off the low frequency signal from the audio signal for analysis.

    I could put a high pass filter in the line so I can limit the low frequency signal to the part of the line it is generated in and then compare the signal on that part of the line to the non-filtered audio signal. This should filter out the audio signal through cancellation and just leave the low frequency signal, which would be great. The problem is I would attenuate low frequencies in the audio signal and reduce the signal quality.

    I am musing that I could use a switched capacitor filter and alternate between high pass and all pass at high (supersonic) frequency - then I could only compare the signals on either side of the filter when it is set to high pass. Maybe this wouldn't work though becuase the switched filter wouldn't have time to respond to a low frequency audio signal when switched so rapidly.

    Any thoughts?


    eddiec :D
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Why go the long way by subtracting the high frequency from the mixed signal to get the low frequency?
    Use a low pass filter to directly get the low frequency components from the mixed signal. If the corner frequency of the low pass filter can be made high enough (while still suppressing the high frequency components sufficiently), there will be negligible attenuation of the low frequency signal.

    It all depends on the exact parameters (spectrum of LF component, spectrum of HF component.

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