Multiband processing is a very powerful way of achieving control on the full frequency spectrum of a track which allows to apply the processing only to a selected part of the audio. This is achieved with the use of filters which split the full frequency range into separate bands. This way processing only affects a selected band while the others are left untouched (if desired). This part of the processing is critical as the nature of the filters used for the frequency splitting is crucial in order to achieve a transparent and natural sounding separation of the bands, where the crossover points don't generate artifacts.
As suggested by its name, Quad Comp is a multiband processor that incorporates up to four fully featured compressors of the Opto type, each one operating on a separate, user-definable frequency band.
Each compressor has a full set of controls allowing to tailor the compression on the band it's applied on to achieve the desired result.
The flexibility of this processor is also augmented by the selectable slope of the filters which can be as broad as 6 dB/Oct or as steep as 24 dB/Oct, for maximum separation.
Even at the steepest slope the filters used in the Quad Comp always sound natural and musical, so that the processing applied to each band doesn't suffer from phasing issues.
The ability to compress each band separately allows you to tame unwanted peaks in a selected portion of the audio spectrum, only if and when a set threshold is exceeded. The possibility to set compression ratio and time constants independently for each band gives you extreme flexibility and precision. Solo and mute buttons make it easy to audition how the compressor is working on a selected band.
Being of the Opto type, the compressor on each band has a smooth compression, very transparent and without side effects, but more aggressive results can be achieved if the threshold and ratio are set accordingly.
The use of this processor is very wide: combining gain reduction with frequency control it can practically act like a “dynamic EQ” as the gain reduction applied on each band depends on whether the level for that frequency exceeds the set threshold.
Most of the times it sits on the stereo master bus of a mix where there is the need to control and even out possible problems with certain frequencies in selected spots of the program; it's also very useful on many other single tracks where frequency content can vary drastically over time and may need to be under control, like vocals or bass.