Sound: Filter (formula)...

A command to convert every selected Sound object into a filtered sound.

The filtering is done in the frequency domain. This command is equivalent to the following sequence:

  1. Sound: To Spectrum... yes
  2. Matrix: Formula...
  3. Spectrum: To Sound

For a comparative discussion of various filtering methods, see the Filtering tutorial.

The example formula is the following:

`if x<500 or x>1000 then 0 else self fi ; rectangular band
`

This formula represents a rectangular pass band between 500 Hz and 1000 Hz (x is the frequency). Rectangular bands are not recommended, since they may lead to an appreciable amount of ringing in the time domain. The transition between stop and pass band should be smooth, as e.g. in Sound: Filter (pass Hann band)....