### 21.3.3 Moving-average filter

The moving_average command applies a moving-average filter to a signal.

- moving_average takes two arguments:
  - A, an array of numeric values representing a sampled signal.
  - n, a positive integer.
- moving_average(A,n) returns an array B obtained by applying a moving-average filter of length n to A. The elements of B are defined by

  B[i]= |
  1
  n
  n−1
  ∑
  j=0
  | A[i+j]

  for i=0,1,…,L−n, where L is the length of A.

Moving-average filtering is fast and useful for smoothing time-encoded signals.

#### Example

snd:=soundsec(2):; noise:=randvector(length(snd),normald,0,0.05):; data:=0.5*threshold(3*sin(2*pi*220*snd),[-1.0,1.0])+noise:; noise_clip:=createwav(data);

a sound clip with 88200 samples at 44100 Hz (16 bit, mono) |  |  |  |  |  |  |  |  |  |

plotwav(noise_clip,range=[1000,1500])

filtered_clip:=createwav(moving_average(data,25)); plotwav(filtered_clip,range=[1000,1500])

You could also listen to the two waveforms by using playsnd with noise_clip and filtered_clip (see Section 28.2.14).