Multiband compression divides the frequency spectrum into different sections, or bands, so that each has its own compression settings.
This allows a longer attack time for the low band of that kick drum to punch through, while maintaining a shorter attack time on a higher band to keep the guitar in check. By using a multiband compressor, it is possible to tailor the compression to the different elements of a mix and compress the recording more transparently than with a standard single-band compressor.
Most multiband compressors have 3 or 4 different bands. Since the cross frequencies define the range of frequencies contained in each band, getting them right can have a big impact on the effectiveness of the compression.
Many multiband compressors have a solo function to focus on one band at a time – this can be very useful when adjusting the crossover frequencies revealing exactly what each band contains.
In addition, soloing individual bands can be useful when setting attack and release times to ensure that the transients in each band have the desired shape.
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Each of these bands represents an individual compressor and has a complete set of controls. All the usual controls are here, such as ratio, threshold, attack and release settings. With the frequency band set, the compressor will only act on the specified frequencies. This is really ideal for dealing with a particular instrument or frequency problem in your mix.