### 21.3.1 Low-pass filtering

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

- lowpass 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).
- lowpass(A,c⟨,r⟩) applies a simple first-order lowpass 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(lowpass(createwav(s),1000))

Output: the sound of the periodic signal after applying a lowpass RC filter with cutoff at 1000 Hz.