### 21.3.2 High-pass filtering

The highpass command applies a simple first-order lowpass RC filter to a signal or audio clip.

- highpass takes two mandatory arguments and one optional argument:
  - A, an audio clip or a real vector representing the sampled signal.
  - c, a real number specifying the cutoff frequency.
  - Optionally, r, a samplerate (by default 44100).
- highpass(A,c⟨,r⟩) applies a simple first-order highpass RC filter to input data and returns the result.

#### Example

To generate a synthetic signal, enter:

f:=unapply(periodic(sign(x),x,-1/880,1/880),x); s:=apply(f,soundsec(3)):;

Then:

playsnd(highpass(createwav(s),5000))

Output: the sound of the periodic signal after applying a highpass RC filter with cutoff at 5000 Hz.