This node performs low-pass filtering of a signal. A low-pass filter passes signal components with a frequency below a given cut-off frequency and rejects the ones above the cut-off. The cut-off input slot expects a cut-off frequency as a fraction of $\pi$. Therefore, it must be in the range $[0.0, 1.0[$. For example, if the cut-off is set to 0.25, only the lower quarter of all possible frequency components passes the filter.
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 cut-off frequency of 0.25. 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.
The example named Lowpass demonstrates the basic usage of this node.