Compression Workshop: A Little Crush
Finding A Pulse
To add a pulse to the room sound, you could insert a compressor on the room mikes or overheads and adjust the compressor for fast attack and release times. The fast release opens back up the compressor and rapidly brings the level back to normal, so it sounds like it’s pumping. This is a classic rock sound – even Led Zeppelin employed this technique.
Another crafty trick is to use the side-chain input, which is sometimes called a key input. This is simply an input for a signal that will serve to control the compressor on another track. Setting the threshold level controls the amount of compression that will be triggered from the key (or side-chain) input.
Preece, who does a lot of electronic and dance music, employs the side-chain input to correct issues, such as frequencies that overlap between tracks, and also as a creative tool to generate a pumping effect in his mixes. In order for the kick and the bass guitar to move out of the way of each other, while both remain present, the side-chain can essentially duck one sound out of the way when the other one dominates, and bring it back up when it’s out of danger of tromping on and murking up the other sound.
Use the kick drum track to control the compressor on the bass to duck it out when the kick is hit. To get the signal on the track to the side chain input on the compressor, you could send it out on an aux send or subgroup. Or if you’re using a half-normalled patchbay, you could split it out from the insert send. Pro Tools gives you the option to use two outputs from the same track in order to send a copy of the signal to the compressor.
Preece generally starts with a moderate approach, setting the ratio to around 6:1. in order to preserve the transient, he adjusts the attack so it’s not too quick, and sets a quick release time to bring the sound back in fast. He then adds make-up gain to bring the sound back up. This also creates an overall pumping pulse to the mix. Setting a short, repetitive percussive sound to trigger the compressor on a track with a steadier, longer duration sound creates an interesting breathing effect in the mix.
Webster, a sound-tweaking experimental madman, enjoys doing a Dr. Jekyll and Mr. Hyde job on drum tracks, ending up with something almost unrecognizable from the original. He often uses between two and ten plug-ins per track in Logic to achieve his nefarious aims. If you want to really go for radical impact with your drum mix, here’s a glimpse at his unsubtle methods.
He uses a compressor to initially even out a track and prepare it to be processed with reverb, distortion, delay, or whatever time-based processing he can think of to morph the sound. After processing the compressed track with a variety of effects, he’ll finish it off with a 4-band compression plug-in to highlight certain sonic aspects, such as the high end from distortion. (Fig. 3) Multi-band compression allows for frequency-specific dynamic control and provides separate compressor controls for several selectable frequency bands. This lets you affect only one section of the frequency content from the original signal or mix.
(Above) Fig. 3. This multi-band compressor plug-in separates the frequency spectrum into four bands. Here the crossover points are set at 100Hz, 1kHz, and 10kHz. This allows for variable compression of different frequency ranges of the signal.
To either emphasize or de-emphasize a specific frequency on a track without messing up the fundamental, Webster recommends employing the side chain for surgical control. Duplicate the audio track so that you have two identical tracks. On the first track, select the frequency to notch or boost with EQ. Send that equalized track into the side-chain input to drive the compressor that you have inserted on the second track.
Notching a frequency with EQ on the side-chain track will emphasize it on the original track. Boosting that frequency will sublimate it on the original track, because the compressor will clamp down on the boosted frequency that is controlling it. This technique keeps the dynamics alive on the track that’s being compressed by almost surgically altering a specific frequency with compression. Overall this has a less-destructive effect than compressing the whole track. This approach could also be used to emphasize natural reverb tails on the original track without adding artificial reverb, which could affect the fundamental frequency.
Serve The Master
When to compress and how to compress? Those are the questions. Whether ’tis nobler for the tune to squash the bejeezus out of your drum mix so it could jump out of the speakers in an F16 cockpit, or to tweak your recorded drums with a few nifty sound-shaping compressor tricks, and by so doing, achieve some cool effects while preserving the dynamic range. It all depends on what you’re going for with your drum sound and what will serve the music best.
Keep in mind that when your overall mix gets mastered, it will undergo an additional round of compression/limiting, so be sure to leave some of that dynamic range intact, even if you are going for audible radio play in an F16.