An envelope follower extracts a control signal that tracks a sound's amplitude contour over time

An envelope follower converts instantaneous amplitude into a slowly-varying control signal tracking the sound’s overall loudness contour. Implementations include rectification plus lowpass filter, running RMS, or running average of absolute values. The smoothing time controls tracking fidelity: fewer samples gives sharper response to transients; more samples gives a smoother curve. The extracted control can be applied to a second sound’s amplitude, a filter cutoff, a delay time, or any other parameter. In Max, average~ in rms or absolute mode implements this; the number of samples determines tracking speed.

Examples

Drum loop envelope applied to a sustained pad creates pumping. Envelope follower on bass bass to lowpass filter cutoff: filter opens on each note attack. Removing a sound’s own envelope (dividing by itself) flattens dynamics, allowing a different envelope to be imposed. Max: average~ (rms) scaled and sent to tapin~/tapout~ creates dynamic-responsive echo.

Assessment

Describe a Max signal chain that uses the envelope of a drum loop to control the cutoff frequency of a lowpass filter applied to a sustained string sound. Name each object and its role.