Adjust the threshold level on the compressor. Anything underneath the threshold set won't be affected by the compressor, where as anything above the threshold will be treated by the compressor. If you want heavy compression on your vocals, set a lower threshold. If you'd like to leave your vocals mostly as is, set a higher threshold. An average threshold for vocals is around seven decibels (dB).
Set the ratio for vocals. A two to one ratio means that if the incoming vocal levels reach 10 dB, the outgoing vocals levels after compression will only reach five decibels. For lighter compression start at a two to one ratio and tweak from there. For more noticeable compression, anything above eight to one is audible to the listener.
Change the attack of the vocals. This setting is measured in milliseconds and represents how quickly the compressor begins taking effect after the vocals have passed through the threshold. Normally for vocals, the attack time is very quick, somewhere in the five millisecond (ms) range, so the compressor can fully compress each word as it is quickly being sung.
Set the release time slower than the attack, somewhere in the 50 ms range. The release time determines how long after the signal hits before the compressor stops processing that sound. Setting the release properly makes the vocal delivery sound more natural, because words tend to naturally drag and echo for a bit after delivery.
Adjust the gain. This is the final step in vocal compression. The gain sets the master output volume of compressed vocals. Raise or lower the gain to suit personal preferences.