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Variable band-stop / notch filters

For a feedback suppression algorithm I am looking to implement variable gain / rejection / frequency notch or band-stop filters.

On other words, I need to be able to control the center frequency and amount of rejection dynamically.

What would be the best way to implement this on an ADAU 1761?

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  • Hi ,

    thank you! for your comprehensive answer!

    I got some important pointers from it - like dynamic calculation of coefficients not being possible on the DSP itself (what a shame btw!  Can't I do this by creating a multiplier/adder/divider network, even if that's tedious?).

    In the meantime I played around with all-pass-filters and adding their output to the original signal.  That will create a very narrow notch at the AP center frequency, as their phase response crosses 180° and thus the signals cancel out.  I can adjust the amount of cancellation by varying the respective magnituses of the AP and the original signal.

    This still leaves moving the center frequency issue to be resolved though.

    Best regards, Roman

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  • Hi ,

    thank you! for your comprehensive answer!

    I got some important pointers from it - like dynamic calculation of coefficients not being possible on the DSP itself (what a shame btw!  Can't I do this by creating a multiplier/adder/divider network, even if that's tedious?).

    In the meantime I played around with all-pass-filters and adding their output to the original signal.  That will create a very narrow notch at the AP center frequency, as their phase response crosses 180° and thus the signals cancel out.  I can adjust the amount of cancellation by varying the respective magnituses of the AP and the original signal.

    This still leaves moving the center frequency issue to be resolved though.

    Best regards, Roman

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