Multi-Band Compression Situations


Imagine you have received a finished mix for mastering but the hi-hats are a little over-powering, and they only appear at certain points in the track. EQ alone may tone them down to bring less attention to themselves, but the effects of the EQ will apply to the whole track, start to finish. EQ will change the texture of the track permanently, which is often the desired effect, but by setting a band on the compressor to be focused on the area of the spectrum where the hi-hats are, you can set the compressor's threshold to be triggered only when the hi-hats become over-powering. It's as if you have access to the mix and have reduced the level of just the hi-hats. Obviously there would be other stray peaks in the highs that would trigger the compressor too from time to time. You need to decide where to strike a balance with your threshold and ratio. The chances are the controlling of these other peaks would be desirable too. For this you will be looking at very fast attack and release times, something perhaps as low as 5ms for the attack, and release as short as 20ms. Set the attack too long and the hi-hat will simply pass by before the compressor has time to control it. Setting the release too long will just sound like you've reduced the hi-hats using an EQ as it will stay in its state of compression until the next hi-hat arrives. The ratio will vary massively, it will depend on how much control you desire. As this effect reduces some top end, you can expect some of the same results as you would with the EQ. A more rounded sound may be obtained, or even warmth, depending on the affected area of the spectrum.

A very good and common use I find for the multi-band compressor is to tighten up a loose, or to control an overpowering low end. Slightly longer attack and release times will be useful here compared to the highs, 40ms attack, 100ms release perhaps. We want a certain amount of transient information to pass in this case as it will be carrying the low end's punch. This tightening of the lows does wonders for translation to the consumer's hi-fi as it improves the low end's punch helping it to be identified on smaller speakers. In some cases, the tightening of the lows can actually allow for the final product to be played at higher volumes before a hi-fi's speakers produce distortion as the reduced dynamic range reduces the actual distance the speaker cone has to travel to produce the low end.

Referring back to 'Limiters and RMS', the use of multi-band across the lows can create a better conditioned mix for the application of limiting to gain high levels of RMS. Multi-band compression is very effective when balance is needed in the low end.

On the next page is a video demonstration of a multi-band compressor in a situation where some control to the low end is required.

When applying multi-band to the midrange frequencies, great care must be taken as there is a high risk of taking the life away. The reason for this is quite simply that almost every instrument in the mix will pass the midrange area and makes up the life of the track. The punch of almost every sound is largely the work of the mids. Sometimes multi-band can be used to tidy up an under-compressed vocal, if it's sitting high enough in the mix. However, compression in this situation may take the impact away from the snare - be careful.

Whereas the single-band compressor is probably the best tool for providing a layer of gel and bringing the mix to a whole, multi-band can certainly be used for that too. In such a case, all compressor bands would be active and fairly light settings will be required. Attack and release times may be similar to what I've mentioned above but ratios will be quite low, similar to single-band, and should probably be the same on each band of frequencies.

Proceed to the next page to see a multi-band compressor in action...

David Eley - TGM Audio

Next page... Demo of Multi-Band Compression