There are many applications in which a multiband compressor can improve the sonic quality of vocal tracks. Here is an example of one pass with a multiband compressing solving two common vocal problems on a track. We’re assuming you recorded your vocals “straight,” with no input processing. This will work with a 2, 3, 4 or 5-band compressor with equal success.
Vocalists often weave closer to and farther away from the mic when recording. This may be intentional; they may do this in live performance to utilize the proximity effect to enhance certain notes. In the studio, however, this can create a problematic track with widely varying bass response and a “wobbly,” inconsistent sound. You could just roll off bass frequencies with an EQ, but that could cause other phrases to sound thin. A multiband compressor, however, can control the proximity effect without reducing fullness when the singer reaches for high notes.
Try this: set your lowest crossover frequency to somewhere between 200 and 300 Hz, which is where boominess usually occurs (depending on the mic, the singer, and the distance between them). Then set that low band’s threshold at a point where it just begins to trigger on vocal phrases that aren’t bass-heavy. Then raise the threshold slightly to make sure those passages pass through the compressor untreated. Any vocal phrases that are even slightly boomy will then exceed the low-band threshold and will be compressed according to your ratio (or range), attack, release, and other settings. And you’ve never touched the singer’s higher registers, so they still sound natural.
It’s easy to de-ess the same vocal track with your multiband compressor. Set your highest compressor crossover to 5 kHz for a male singer or to 6 or 7 kHz for a female vocalist. Then set the high-band threshold so that only
sibilant phrases trigger in-band compression. De-essing usually requires a high ratio (often 10:1 to 50:1), a high range (up to 20 dB of gain reduction for extreme cases), or both. Of course, look for the least obtrusive settings possible – a much lighter treatment should work with subtle problems. Set your high-band attack time as fast as possible (try 50 microseconds) and set the release time to between 50 and 60 milliseconds.
Listen as the track plays and reduce or increase the ratio and range as necessary. Remember that you don’t want a ratio that so low it makes all the high frequencies sound dull; likewise your gain reduction shouldn’t be too obvious (a symptom known as “pumping“). You shouldn’t have to play with attack and release times too much since you’re just working to remove the initial attack sibilance.