Compressor

The Compressor is designed to emulate the sound and response of a professional-level analog (hardware) compressor. It tightens up your audio by reducing sounds that exceed a certain threshold level, smoothing out the dynamics and increasing the overall volume—the perceived loudness. Compression helps bring the key parts of a track or mix into focus, while preventing softer parts from becoming inaudible. It is probably the most versatile and widely used sound-shaping tool in mixing, next to EQ.

You can use the Compressor with individual tracks, including vocal, instrumental, and effects tracks, as well as on the overall mix. Usually you insert the Compressor directly into a channel strip.

Compressor Parameters

The Compressor offers the following parameters:

Figure. Compressor window.
  • Gain Reduction meter: Shows the amount of compression in real time.
  • Attack knob and field: Determines the amount of time it takes for the compressor to react when the signal exceeds the threshold.
  • Compression curve display: Shows the compression curve created by the combination of Ratio and Knee parameter values. Input (level) is shown on the x axis and output (level) on the y axis.
  • Release knob and field: Determines the amount of time it takes for the compressor to stop reducing the signal after the signal level falls below the threshold.
  • Auto button: When the Auto button is active, the release time dynamically adjusts to the audio material.
  • Ratio slider and field: Sets the compression ratio—the ratio of signal reduction when the threshold is exceeded.
  • Knee slider and field: Determines the strength of compression at levels close to the threshold. Lower values result in more severe/immediate compression (hard knee). Higher values result in gentler compression (soft knee).
  • Compressor Threshold slider and field: Sets the threshold level—signals above this threshold value are reduced in level.
  • Peak/RMS buttons: Determine whether signal analysis is with the Peak or RMS method, when using the Platinum circuit type.
  • Gain slider and field: Sets the amount of gain applied to the output signal.
  • Limiter Threshold slider and field: Sets the threshold level for the limiter.
  • Limiter button: Turns the integrated limiter on or off.

Using the Compressor

The following section explains how to use the main Compressor parameters.

Setting the Compressor Threshold and Ratio

The most important Compressor parameters are Threshold and Ratio. The Threshold sets the floor level in decibels. Signals that exceed this level are reduced by the amount set as the Ratio.

The Ratio is a percentage of the overall level; the more the signal exceeds the threshold, the more it is reduced. A ratio of 4:1 means that increasing the input by 4dB results in an increase of the output by 1dB, if above the threshold.

As an example, with the Threshold set at -20 dB and the Ratio set to 4:1, a -16 dB peak in the signal (4 dB louder than the threshold) is reduced by 3 dB, resulting in an output level of -19 dB.

Setting Suitable Compressor Envelope Times

The Attack and Release parameters shape the dynamic response of the Compressor. The Attack parameter determines the time it takes after the signal exceeds the threshold level before the Compressor starts reducing the signal.

Many sounds, including voices and musical instruments, rely on the initial attack phase to define the core timbre and characteristic of the sound. When compressing these types of sounds, you should set higher Attack values to ensure that the attack transients of the source signal aren’t lost or altered.

When attempting to maximize the level of an overall mix, it is best to set the Attack parameter to a lower value, because higher values often result in no, or minimal, compression.

The Release parameter determines how quickly the signal is restored to its original level after it falls below the threshold level. Set a higher Release value to smooth out dynamic differences in the signal. Set lower Release values if you want to emphasize dynamic differences.

Important: The discussion above is highly reliant on not only the type of source material, but also the compression ratio and threshold settings.

Setting the Compressor Knee

The Knee parameter determines whether the signal is slightly, or severely, compressed as it approaches the threshold level.

Setting a Knee value close to 0 (zero) results in no compression of signal levels that fall just below the threshold, while levels at the threshold are compressed by the full Ratio amount. This is known as hard knee compression, which can cause abrupt and often unwanted transitions as the signal reaches the threshold.

Increasing the Knee parameter value increases the amount of compression as the signal approaches the threshold, creating a smoother transition. This is called soft knee compression.

Setting Other Compressor Parameters

As the Compressor reduces levels, the overall volume at its output is typically lower than the input signal. You can adjust the output level with the Gain slider.

You can also use the Auto Gain parameter to compensate for the level reduction caused by compression (choose either -12dB or 0dB).

When you use the Platinum circuit type, the Compressor can analyze the signal using one of two methods: Peak or root mean square (RMS). While Peak is more technically accurate, RMS provides a better indication of how people perceive the signal loudness.

Note: If you activate Auto Gain and RMS simultaneously, the signal may become oversaturated. If you hear any distortion, switch Auto Gain off and adjust the Gain slider until the distortion is inaudible.