Using Multi-band Compression On Synths
Because synthesizers are electronically generated sources that can be controlled in level via MIDI velocity, it may seem that there's little need to compress them, but there are occasions on which compression can be of benefit. Furthermore, there are times when multi-band compression will yield better results than full-band compression. For example, take the case of a sound based around a resonant filter sweep. If you apply full-band compression to tame the (often significant) increase in peak level at the sweep's centre frequency, the whole sound is reduced in level, sometimes dramatically. In this instance, multi-band compression may yield more transparent results by keeping the peak under control, but without changing the level in the other frequency bands. In the case of a three-band compressor, this means that heavy compression will only ever be occurring in one of the three bands at any one time.
Level peaking may also occur when two sounds are beating with each other or where a flange effect is being applied (due to the peaks and troughs caused by comb filtering), and though full-band compression will control the level, a multi-band compressor will do so much more transparently. A similar situation exists when you have a bass synth sound that also has a lot of higher harmonics. By using a multi-band compressor, the bass end (which is where most of the energy resides) can be kept at an even level without the level of the higher frequencies pumping up and down in sympathy.