Common uses for multiband dynamics
Often, the best indication that you need multiband compression or dynamic EQ is when static EQ doesn’t give you the results you need – for example, if a mix needs more high-frequency air, but boosting with a high shelf makes certain elements too bright or too prominent. In this case, using a dynamic high shelf, or the highest band of a multiband compressor, can provide a boost that automatically flattens out (or becomes a cut) when those high frequencies get too loud. Compressing just the high frequencies in this way can add a glossy sheen to a mix, making it sound bright and airy without becoming splashy or sibilant.
If the mix sounds harsh in places, it may help to compress the upper midrange, dynamically cutting the harshness when it occurs without dulling the sound the rest of the time.
Boxiness or muddiness can often be tackled with dynamic processing of the lower midrange. Compressing this region can sometimes help, but if you’re trying to clear congestion, gentle downward expansion can often work better. Compressing the bass or sub bass can give your mix a much more consistent bottom end, and is particularly effective with very bass-heavy genres. However, expansion might be a better option if you find that your bass sounds boomy but the kick drum sounds light and lacks lowend punch.
Attack and release parameters are just as important with multiband as full-band compression, even though it’s harder to hear their effects. Inappropriate settings might introduce subtle issues that you don’t notice till it’s too late. Low bass frequencies are inherently slower than high treble frequencies, so you’re often likely to need slower compression settings for lower bands. If you do use fast release times for low bass frequencies, make sure to listen out for distortion.
Put simply: use your ears! A slower attack time for the low band might give the kick more low-end thump, for example, while a faster attack for the mid band might tame hard consonants in a vocal part.
When you’re using expansion, try to stick to fairly fast attack times in order to preserve punch. A bit of lookahead can also be helpful in this case.