This node performs band-reject filtering of a signal. A band-reject filter rejects signal components with frequencies within a certain range and passes the ones outside the range. The filter rejection range is defined by the two input slots lower cut-off and upper cut-off, which expect their values as a fraction of $\pi$. Therefore, they must be in the interval $[0.0, 1.0[$.
Currently, there are five different filter approaches implemented that can be selected via the approach slot:
  • Approach = 0: Hamming windowed-sinc filter
  • Approach = 1: Blackman windowed-sinc filter
  • Approach = 2: BlackmanNuttal windowed-sinc filter
  • Approach = 3: Lanczos windowed-sinc filter
  • Approach = 4: Butterworth IIR filter
Freq. response in dB
The diagram above shows the frequency response of different approaches for a lower cut-off of 0.25 and upper cut-off of 0.5. It can be observed that the approaches have different roll-offs and rejection band attenuations. The IIR Butterworth filter performs worst but is an order of magnitude faster to execute.
The quality input slot controls the length of the filter. A larger quality value will typically result in better filter performance but longer computation times.