Amplitude Envelope Follower

An envelope follower will essentially determine the amplitude envelope without dipping down into the valleys/zero crossings.

It is a reduction of the information, representing the overal shape of the signal's amplitude (i.e. amplidtude envelpe) without the higher frequency information.

The amplitude envelope $y(n)$ is given by

$$y(n) = (1-\nu)\vert x(n)\vert + \nu y(n-1),$$

where $\nu$ determines how quickly changes in $x(n)$ are tracked:

• if $\nu$ is close to one, changes are tracked slowly
• if $\nu$ is close to zero, $x(n)$ has an immediate influence on $y(n)$.

In order to capture attacks in the signal, the value for $\nu$ is usually smaller for an increasing signal and large for one that is decreasing.

See envfollower.m