Plug a microphone cable into the speaker's microphone. Plug the other end of this cable into the input of the compressor. Connect the compressor's output cable to the input of your PA system.
Increase the compressor's input gain until the microphone's signal reaches the desired level of loudness.
Adjust the compressor's threshold control as the speaker talks into the microphone. Set the threshold so that the compressor turns on when the speaker begins to speak louder. This will cause these louder passages to be compressed, delivering a more consistent signal to the PA system. The compressor will only turn on when the input level surpasses the threshold; otherwise, the signal will remain unaffected.
Adjust the compression ratio depending on how much you want to compress the signal when it surpasses the threshold. For instance, when the compressor is set to a ratio of 5:1, the compressor will allow an increase of 1 decibel in volume for every 5 decibels the signal goes over the threshold. The higher the compression ratio, the more severely the compressor will compress the speaker's voice. The lower the compression ratio, the more smoothly the compressor will compress it.
Set the attack and release controls of the compressor to determine how quickly the compressor turns on and off after the threshold has been crossed. The shorter the attack time, the more quickly the compressor will engage after the threshold has been passed. The shorter the release time, the more quickly the compressor will disengage after the signal has fallen below the threshold.
Adjust the compressor's output gain to make up for any gain lost through compression.