The external sidechain enables the compressor to control its processing totally independent from the audio material running through it. If the SC Extern switch is active, compression will not be triggered by the signals from the regular audio inputs anymore, but by different signals which are fed into the additional sidechain input connectors.
If, for example, a duplicate of the input signal is processed with an equalizer and then fed into the sidechain input, the result will be frequency-dependent compression. Another example is to send the bass drum of a drum machine into the sidechain input in order to achieve nice groovy compression that is pumping in sync with the music.
The creative options are almost infinite. Compression can be exactly on time or totally against it, which can of course be varied on the fly. Single instruments can be given more space in a mix according to its rhythm. All of a sudden, static sounds become vivid and sound really interesting!
In addition to the external sidechain input the xpressor features a send output, which can be used to feed a summed copy of the input signals e.g. to an EQ and then into the sidechain input – additional sends from the DAW or the console are no longer needed.