Unity gain staging
In mixing, unity gain staging is the process of taking a set of audio stems and clip gaining them up or down to roughly match the producer’s mix, while keeping the track faders at zero.
For example, here’s a Logic Pro file for a mix of mine (not my own song):
First notice at the bottom that all of the faders are at 0 dB. Then notice at the top left, it says “Gain: * ”. Given the producer’s mix, I have adjusted the gain of each of the clips (stems) such that they’re about what I hear back in the producer’s mix.
Rarely will this result in an identical sound because the producer’s mix will include FX like limiting.
Not only is this a great ear training exercise, it also allows you to start mixing where the producer left off.