Compression

For this week's assignment in the Introduction to Music Production class on Coursera, I'm going to show you how to apply compression to an audio track in a Digital Audio Workstation (DAW).

I'll demonstrate compression with a drum track.  First, while playing the track and observing its waveform, I decrease the threshold until it is below the peaks I woud like to compress.  This threshold determines the amplitude at which the compressor is activated.  Then, I increase the compression ratio - this determines the amount of compression that is applied.  Initially, I set it too high, and the drum track loses all of its dynamics.  I then dial it back until I achieve the desired balance between all of the drum kit elements in the track.  Note how the display shows the input sound as a faint waveform in the background, and the output sound as the waveform in the foreground:

The compressor has removed the transients from the beginning of the kick and snare drum hits, and I would like to bring them back.  To do this, I adjust the attack time - this determines how quickly the compressor is activated after the input rises above the threshold.  I turn the attack knob to the right, increasing the attack time until I can hear enough of the transients - this restores some of the punchiness to the track.  Note that the first display (gain reduction) shows a slight change in the speed at which the compressor reduces gain (see the yellow line at the top of the display.  The second display now shows that the output contains those transients, which rise above the compressor threshold:

Finally, I want to set the release time of the compressor - this determines how quickly the compressor is deactivated after the input falls below the threshold.  Initially, I set the release time too high and the compressor releases too slowly, flattening the dynamics of the track.  I then bring it back down to a speed that achieves smooth transitions and avoids the pumping effect that is caused by very short release times:

There is no one-size-fits-all recipe for applying compression - every project will present different requirements, so the desired results can only be achieved through experimentation.

Thanks for watching!