Here’s a video showing basic techniques with loops and loop envelopes in Ableton Live.There’s a part two arriving soon, showing more esoteric ways to manipulate the loops, too.
In case things happen too fast in the video, I’m using command-B to switch between paint mode and linear editing mode in the envelope window.
PS: The reverb in the voice track was an experiment. Alas, I will not use that in future :-).