How to a make one signal have the same dynamic envelope as a second?

Question

I want to take a piece of music and edit it so that it has the same or similar loudness and softness at each sample point as another piece of music. A sidechain compressor restructures one signal based on the envelope of a second, but inversely, so one is loud while the other is quiet. I want to do the opposite of this, making one loud when the other is loud and soft when the other is soft, there by approximating the dynamic envelope. An example of this is the backward voices in Bluejay Way by the Beatles that fade in and out with the music. I was also wondering if there is a midi version of this that would impart the adsr envelope of one signal to another. Thanks~ Elliott

Answer 1

what you are asking for can be built with a DSP (Digital Signal Processor) equipped with A/D (Analog to Digital) and D/A (Digital to Analog) converters.

Then you write a program inside the DSP to take the envelope of one signal and multiply it times the other signal and output the other signal with a varying gain.  There are all sorts of issues that need to be considered such as attach and decay times, filtering, etc.

This can also be done with analog circuits, by filtering the first signal for its envelope and then feed the result into a voltage controlled gain circuit which would modulate the second signal.