Compress your drum sub-mix
Words: Andy McGirr
Compression is a form of automatic volume control whereby when a signal passes a predetermined level (threshold), the level is automatically attenuated. How much it is attenuated by is determined by the ratio setting on the compressor. This results in the overall dynamic range of the sound being reduced – the quiet parts closer in volume relative to the loudest parts.
Compressing a group of drums can add adhesion to the sounds within the group, creating a more uniform and balanced feel. Careful application over a drum sub-mix can add more punch and allow the drums to cut through cleaner. If your drum sub-mix contains percussive instruments with varying levels, possibly those played and recorded live, compression can help to even out the levels and avoid these drum instruments from popping out of the mix or being too quiet at points. Controlling the level of vocals with compression is also used heavily, as the vocalist may have too much dynamic range in a recording.
There’s an abundance of hardware and software compressors on the market. However, any compressor will do a respectable job if set up properly so to begin, opt for whatever comes with your DAW.
The first port of call is the threshold. While the drums are playing, reduce the threshold value until you see a gain reduction of around two to four dB, any more and you’ll risk squeezing the life out of the drums. If the compressor has an auto-release (ARC) option use it, as the varying drum transients will make it difficult to set a fixed amount manually. The ARC function has a look-ahead algorithm that counteracts this issue. When setting the ratio, increase the value in small increments. Too high a ratio setting will result in the compressor acting more like a limiter. For drums, a ratio setting of 4:1 is a good starting point.
Getting the ‘attack’ setting correct will have the biggest impact on the resulting sound output. This determines how quickly the compressor will begin to attenuate the signal once the threshold has been passed. A very low setting will prevent the transients from passing through unaffected and will result in loss of snap or punch in the drums. Start around 30m/s then fine-tune to taste.
The next step is to apply ‘make-up gain’, which boosts the overall output of the compressor so that the level can be matched to the same as the input level, leaving the overall level of the output signal the same as the input. However, the output signal may be perceived as louder due to the fact the dynamic range has been reduced and the quieter drum parts are now closer in volume to the louder parts.
Finally, when setting the compressor use the bypass option to make a quick comparison between the compressed sub-mix and uncompressed signal. This helps to gauge if the compressor and the settings are giving the desired effect.
Andy McGirr is the co-founder of Curate Records.