# Sidechain Compressor

## Functionality

A sidechain compressor acts like a normal (wideband) compressor but has the ability to filter the detected signal before sendig it to the compression stage.
Normally a compressor uses the full range signal to detect a level above the threshold. A sidechain compressor provides a filter (or equalizer) for the detection signal to reduce the bandwidth or to remove some frequencies from it. For example: If you cut all lower frequencies from your detection signal the compressor will decrease the volume of your track only if some loud highs appear. With this technique you are able to reduce the consonants of a vocal track, remove "rumbling" of single notes from a bass guitar or level the dynamics between an clean and a distorted guitar on a single track.

## Sidechain

Calf Sidechain Compressor provides two independent filters to give complete control over the sidechain signal. You can listen to the filtered signal through the "S/C Listen" button to set the filters values exactly. The filters' LED's display the status of them. A blue light shows a bell or shelving filter, red light indicates a high-, low- or bandpass.

## Split

For deessing or derumbling you can choose a "split" mode from the list, too. While in this mode only one filter is set to active. Choose a split frequency with this one. The other filter is used internally to split the signal to be compressed at the same frequency as the sidechain filter. After compressing the chosen frequency range through the (also filtered) sidechain it is added to the untouched frequency range again. Split mode gives you the ability to reduce a defined frequency range without affecting other frequencies. It can be useful for example to reduce an outstanding crash cymbal on a bassdrum in a mixdown without affecting the pressure of the kick. Or perhaps to level sharp consonants on a recording of a choir. It also may add some missing "air" in a vocal recording, a strings track or whatever without raising attacks or loud enough heights.

## More

A specialized version of the sidechain compressor is the deesser. It works mostly like a sidechain compressor but with specialized settings to be more effective on vocal tracks or high frequency compression.
If you have a signal containing complex or wideband frequency ranges and have problems in different ranges then a multiband compressor could be the right choice.
For more information about compression and the essential values please refer to the compressor's manual.

## Controls

- Bypass: Don't process anything, just bypass the signal
- Input (knob): Raise the volume before the signal is sent in the compression stage. If you have found some great settings but want to raise the overall loudness of the track simply increase this level.
- Input (VU-meter): The level of the original signal
- Input (LED): Flashes if the level of the original signal raises above 0dB (it doesn't clip your signal)
- Output (VU-meter): The level of the compressed and made up signal
- Output (LED): Flashes if the level of the output signal raises above 0dB (it may clip your signal depending on your host and your systems' bitrate!)
- Attack: Amount of milliseconds the signal has to rise above the threshold before gain reduction starts
- Release: Amount of milliseconds the signal has to fall below the threshold before the reduction is decreased again
- Knee: Curve the sharp knee around the threshold to enter gain reduction more softly
- Ratio: Set a ratio about which the signal is reduced. 1:2 means that if the level rises 4dB above the threshold, it will be only 2dB above after the reduction.
- Threshold: If a signal rises above this level it will affect the gain reduction
- Makeup: Amplify your signal after processing
- Stereo Link: Choose if the average level between both channels or the louder channel affects the reduction
- Detection: Choose if the deesser should take the exact signal for detection or an RMS like one (it's mainly smoother).
- Gain Reduction: The level of reduction on the original signal
- Sidechain Mode: The selection of filters to use in the sidechain
- S/C Listen: Route the filtered sidechain signal to the output for monitoring purposes
- F1 active: Displays the status of filter #1: Off - off, blue - bell or shelving, red - band-, high- or lowpass
- F1 Freq: The frequency of filter #1
- F1 Level: Increase or decrease the chosen frequencies
- F2 active: Displays the status of filter #2: Off - off, blue - bell or shelving, red - band-, high- or lowpass
- F2 Freq: The frequency of filter #2
- F2 Level: Increase or decrease the chosen frequencies