I'm trying to filter out line noise(60Hz and 120Hz) from a EEG signals received over a bluetooth link. I'm proposing to use a IIR notch filter to filter out the line-noise which varies w.r.t to distance between the bluetooth transmitter and receiver. I'm not able to establish a clear relationship between the Notch filter parameters and the magnitude of line noise so as to avoid over-attenuation or under-attenuation to avoid dips and peaks at these frequencies in the spectrum. The problem is Q-factor and stop-band Bandwidth which define the notch filter don't directly relate to the stop band attenuation. If this is not possible is there any other equally efficient adaptive stop-band filtering method to achieve the same ? How can this be implemented w.r.t line noise measurement and corresponding filter parameter adjustments ?

  • $\begingroup$ A notch filter always has infinite attenuation at its notch frequency. Its only parameter is its bandwidth, which determines the transition from zero gain at the notch frequency to some defined gain greater than 0. Don't you always want to completely zero out the line noise? $\endgroup$ – Matt L. Dec 13 '14 at 22:42
  • $\begingroup$ There might be some functional brain information present in in the 60 Hz region and surrounding frequencies. I believe the IIR notch filter is not linear phase, but is there any possibility of recovering the functional information content at this frequency if the signal is not over-attenuated at 60Hz ? $\endgroup$ – Naveen Dec 13 '14 at 23:02
  • $\begingroup$ I guess you have to try to eliminate the line noise as completely as possible using a narrow band notch filter. $\endgroup$ – Matt L. Dec 13 '14 at 23:12

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