A compressor is provided for all the available microphone inputs.
Compression can be used to control the level from a microphone, to help compensate for different presenters who will naturally have their own speech level and may speak at different distances from the microphone. For the purposes of controlling announcement microphones, it is generally best to use compression gently.
The threshold determines the level at which compression starts to work. Essentially, when the quietest person speaker there should be no compression, and the compression should be set to bring louder voices in line with this voice. Set the threshold control accordingly, using the slider.
A ration of about 5 or 6:1 is a good start, meaning that for every 5 or 6dB of volume increase over the threshold, the compressor will only allow 1dB. Set the compression ratio using the slider. To engage the compressor, check the 'Enable compressor' box. Make the comparison between compressed and uncompressed by talking and switching the compressor on and off.
The Attack and Release controls affect how the compressor works over time. A fast attack time will affect the initial transients of the audio signal, whilst a slower attack will allow initial transients through and compress the audio signal afterwards. The release time determines how quickly the compressor returns to the uncompressed state after the signal has dropped below the threshold. If in doubt, an attack time of around 5 - 10ms and a release time of around 40ms will work for most applications.
Checking the 'Enable auto makeup gain' box will compensate for any gain reduction introduced by using the compressor.
WARNING: Heavy compression in combination with auto makeup gain may cause acoustic feedback problems.