Rectifying a signal

Audacity 2.1.0

I have an audio signal of which I would like to retrieve just the amplitude in a kind as if I would rectify the signal to a half wave and then send this to a low pass filter. I’m just interested in the peak amplitude envelope.
How can I achieve this?


There’s a rectify plugin for Audacity here … Rectivert - Rectification and Inversion
(It does full & half-wave rectification)