Key Of Grey

September 7th, 2009 – Have you ever had to work with source material that you couldn’t go back and mix again? Perhaps a client has brought you a track to master, or you are remixing a track for a DJ set and you want tighter and heavier bass. What you need is a multipressor.

A multipressor is a compressor that allows you to slice up the source material into frequency ranges and independently compress each portion. Of course, to understand what I just wrote, you’ll have to know what a compressor does. Imagine that you have a sound file that varies wildly in volume. You cannot increase the volume of the whole track to hear the quiet parts, because the loud parts will peak. There are two ways to deal with this problem: (a) you can automate the volume manually throughout, increasing the volume for the quiet parts and decreasing it for the loud parts, and (b) compress the whole track and let the compressor do the work.

For the purposes of this post, I’m not going to go over the use of compressors to impart a specific “sound” on audio in this article, we are only dealing with compressors as a way to control volume. A compressor allows you to set a threshold that triggers it to take action. For example, above a certain decibel threshold, the compressor will reduce the gain by a third. For a more thorough explanation of how compressors work, check out this video post on the always awesome HomeStudioCorner.

Compressors are great at dealing with an individual instrument, but sometimes you’re working with a track that contains multiple recorded instruments together and you don’t want everything to be loud, you only want certain sounds to be loud. For example you want the bass to be much heavier, but you don’t want to touch the high end. This is where you’d use a multipressor to independently compress frequency ranges. In the Logic multipressor you see above, I’ve sliced the track into 4 sections, each with separate compression settings.

Usually, you’ll use a multipressor on a stereo track of audio that consists of many tracks that have already been summed to one left and right track. This means that generally you’ll use it at the mastering stage. However, there are some other situations where you might use it on just one instrument. For example, a multipressor might be useful on a recorded acoustic piano. Since pianos cover quite a range of frequencies and may have percussive elements that are more prominent in certain ranges of the instrument, a multipressor might be used judiciously to good effect.

Any questions?

Update : AudioTuts has a good article on how multipressors work.