Apple Using WaveBurner Pro 1.0 (with Logic Pro) - Manual (Page 28)

28
Multipressor
The Multipressor (short for multiband compressor) is used as a mastering tool in many
different situations. The Multipressor splits the incoming signal into two to four
different frequency bands, each of which is compressed independently. This permits
higher levels of compression without producing a pumping effect.
As the name suggests, the Multipressor is like a set of compressors, each working
independently on a different part of the frequency range of an input signal. For each
frequency band, you set the Threshold, Ratio, Attack, and Release parameters as with the
Compressor. Using the Multipressor allows you to raise the overall volume level, which
can dramatically increase the amount of low-level noise (known as the noise floor).
To reduce the noise floor, each frequency band features Expansion (also called
downward expansion), which acts as a counterpart to the compressor for that band. The
compressor decreases the dynamic range at higher volume levels, and Expansion
increases the dynamic range at lower volume levels. When you apply Expansion, the
signal is reduced when it is lower than the threshold. The effect is similar to a noise
gate, but instead of cutting off the sound abruptly, it smoothly fades the volume using
an adjustable ratio.
The Multipressor has several other important parameters, including Bands and
Lookahead. The Bands parameter lets you choose whether two, three, or four
independent frequency bands are compressed; the higher the number, the more
processing power the Multipressor uses. Classic multi-band compressors typically use
three bands.
The Lookahead parameter lets you control how far ahead in time from the current
point in the signal the Multipressor “looks” or analyzes the signal, allowing it to react
more quickly to peak volumes. Unlike hardware compressors, using Lookahead does
not cause a delay in the signal, because the Multipressor can read the audio file on disk
and does not need to analyze the signal in real time.