The Multipressor (an abbreviation for multiband compressor) is an extremely versatile
audio mastering tool. It splits the incoming signal into different frequency bands—up to
four—and enables you to independently compress each band. After compression is
applied, the bands are combined into a single output signal.
The advantage of compressing different frequency bands separately is that it allows you
to apply more compression to the bands that need it, without affecting other bands. This
avoids the pumping effect often associated with high amounts of compression.
As the Multipressor allows the use of higher compression ratios on specific frequency
bands, it can achieve a higher average volume without causing audible artifacts.
Raising the overall volume level can result in a corresponding increase in the existing
noise floor. Each frequency band features downward expansion, which allows you to
reduce or suppress this noise.
Downward expansion works as a counterpart to compression. Whereas the compressor
compresses the dynamic range of higher volume levels, the downward expander expands
the dynamic range of the lower volume levels. With downward expansion, the signal is
reduced in level when it falls below the threshold level. This works in a similar way to a
noise gate, but rather than abruptly cutting off the sound, it smoothly fades the volume
with an adjustable ratio.