The compressor reduces the gain of an output channel when the audio signal reaches the level specified by the Threshold parameter. The gain of the channel will be progressively reduced as the signal increases above the threshold, according to the Ratio parameter. This can be used to limit the power delivered to speakers and thus reduce the risk of damage from overdriving.
This screenshot shows an example Compressor setting:
(Note that the compressor algorithm is bypassed by default, so click on the Bypass button to see the curve as shown here.)
In this example, the threshold is set to −20 dB, so the compressor will activate when the signal on that channel reaches −20 dB (relative to full output). The ratio is set to 2, so if the input signal level to the compressor then increases by 10 dB, the output level will increase by only 5 dB. If the input signal level to the compressor is at full scale (0 dB), then the output level will be limited to −10 dB.
Two additional parameters control the action of the compressor: the attack time and the release time. These two parameters govern how quickly the compressor activates when the signal level exceeds the threshold, and how quickly it deactivates when the signal level reduces. The optimum settings may need to be tuned by ear. For more information, see the Wikipedia article Dynamic range compression.
The compressor block is disabled by default. To enable it, click on the Enable Compressor switch. The graph will change from a dashed grey line (disabled) to a solid colored line (enabled).
Keyboard and mouse operations¶
Parameters can be edited by:
- Clicking and dragging on a slider. Once the focus is on a slider, you can also change the value with the left and right arrow keys on the keyboard.
- Clicking in the value field and typing a new value. Once the focus is in a value field, you can also change the value with the up and down arrow keys on the keyboard.
- Move the mouse cursor over the parameter and use the mouse scroll wheel or equivalent gesture on a trackpad.
The Tab key will move focus between fields; Shift-Tab will move in the opposite direction.
Jumping between channels¶
To jump quickly between the compressor window of different channels, enable the Menu switch at the top right. Jump to a different channel by clicking on the row of buttons: