Intro to Multipressor in Final Cut Pro
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.
Multipressor allows the use of higher compression ratios on specific frequency bands, so 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.
In the graphic display, the blue bars show the gain change—not merely the gain reduction—as with a standard compressor. The gain change display is a composite value consisting of the compression reduction, plus the expander reduction, plus the auto gain compensation, plus the gain make-up.
Setting compression parameters
The Compression Threshold and Compression Ratio parameters are the key parameters for controlling compression. Usually the most useful combinations of these two settings are a low Compression Threshold with a low Compression Ratio, or a high Compression Threshold with a high Compression Ratio.
Setting downward expansion parameters
The Expansion Threshold, Expansion Ratio, and Expansion Reduction parameters are the key parameters for controlling downward expansion. They determine the strength of the expansion applied to the chosen range.
Setting Peak/RMS and Envelope parameters
Adjusting the parameter between Peak (0 ms, minimum value) and RMS (root mean square −200 ms, maximum value) is dependent on the type of signal you want to compress. An extremely short Peak detection setting is suitable for compression of short and high peaks of low power, which do not typically occur in music. The RMS detection method measures the power of the audio material over time and thus works much more musically. This is because human hearing is more responsive to the overall power of the signal than to single peaks. As a basic setting for most applications, the centered position is recommended.
Setting output parameters
The Out slider sets the overall output level. Set Lookahead to higher values when the Peak/RMS fields are set to higher values (farther toward RMS). Set Auto Gain to On to reference the overall processing to 0 dB, making the output louder.