Multipressor

The Multipressor (short 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 simply cutting off the sound, it smoothly fades the volume with an adjustable ratio.

Multipressor Parameters

The parameters in the Multipressor window are grouped into three main areas: the graphical display in the upper section, the set of controls for each frequency band in the lower section, and the output parameters on the right.

Figure. Multipressor window.
Multipressor Graphical Display Section
  • Graphical display: Each frequency band is represented graphically. The amount of gain change from 0 dB is indicated by blue bars. The band number appears in the center of active bands. You can adjust each frequency band independently in the following ways:
    • Drag the horizontal bar up or down to adjust the gain makeup for that band.

    • Drag the vertical edges of a band to the left or right to set the crossover frequencies, which adjusts the band’s frequency range.

  • Crossover fields: Set the crossover frequency between adjacent bands.
  • Gain Make-up fields: Set the amount of the gain make-up for each band.
Multipressor Frequency Band Section
  • Compr(ession) Thrsh(old) fields: Set the compression threshold for the selected band. Setting the parameter to 0 dB results in no compression of the band.
  • Compr(ession) Ratio fields: Set the compression ratio for the selected band. Setting the parameter to 1:1 results in no compression of the band.
  • Expnd Thrsh(old) fields: Set the expansion threshold for the selected band. Setting the parameter to its minimum value (-60 dB), means that only signals that fall below this level are expanded.
  • Expnd Ratio fields: Set the expansion ratio for the selected band.
  • Expnd Reduction fields: Set the amount of downward expansion for the selected band.
  • Peak/RMS fields: Enter a smaller value for shorter peak detection, or a larger value for RMS detection, in milliseconds.
  • Attack fields: Set the amount of time before compression starts for the selected band, after the signal exceeds the threshold.
  • Release fields: Set the time required before compression stops on the selected band, after the signal falls below the threshold.
  • Band on/off buttons (1, 2, 3, and 4): Enable/disable each band (1 to 4). When enabled, the button is highlighted, and the corresponding band appears in the graphical display area above.
  • Byp(ass) buttons: Enable to bypass the selected frequency band.
  • Solo buttons: Enable to hear compression on only the selected frequency band.
  • Level meters: The bar on the left shows the input level, and the bar on the right shows the output level.
  • Threshold arrows: Two arrows appear to the left of each Level meter.
    • The upper arrow adjusts the Compression Threshold (Compr Thrsh).

    • The lower arrow adjusts the Expansion Threshold (Expnd Thrsh).

Multipressor Output Section
  • Lookahead value field: Adjusts how far the effect looks forward in the incoming audio signal, in order to react earlier to peak volumes, and therefore achieve smoother transitions.
  • Out slider: Sets the overall gain at the Multipressor output.
  • Level meter: Shows the overall output level.

Using the Multipressor

In the graphical 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 Multipressor 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 Multipressor 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 Multipressor 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 Multipressor 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.