I’m going to discuss how compression and limiting works, but how you utilize it really comes down to what you are trying to achieve by using it. I have always said I can teach you what compression does in a day, but how you use it can take a lifetime.
There are many manufacturers of compressors/limiters and some work well and others do not. They can be very expensive to very cheap in monetary cost, but for the most part you get what you pay for. I have used some cost effective compressors that get the job done and don’t sound half bad, such as the ART Pro VLA II. I was surprised for the cost how well it performed. The ones we tend to use in pro studios sound the best, but cost the most and each one has its own character, so to speak.
A few different manufacturers you tend to see in pro studios will include, but not limited to: DBX, Manley, Focusrite, and Universal Audio just to name a few. What makes a high-end compressor different from a cost effective compressor? It is based on the design and parts that are used to manufacturer it, but it really comes down to how well it performs the task and how good does it sound once the task has been performed. What is the task you ask? Simply said, it is used to control the dynamic range of a sound. To make the quiet parts louder to compete in volume with the lower level sounds or to control peak activity “sounds that get too loud and distorts the audio.”
Compression vs Limiting
Compression starts at a ratio of 1.1 to 1 and goes up to 3.9 to 1. This means that if we had a ratio of 2 to 1 for every 2dB that went into the compressor 1dB came out. If we had 20dB going in at a ratio of 2 to 1 we would have 10dB coming out of the compressor. What does this do..? It will bring up the lower level “quieter section” of the sound to compete with the louder level signal. Take a human voice for instance. If I speak quietly into a microphone and it comes in around -10dB on our VU meter, then I yell into the microphone and that comes in around 0dB on the VU meter, there is a 10dB difference in dynamics. I wont hear the quiet part of the voice as well as the louder part when it is played back. It may get lost in the mix by the other instrumentation. I would use a compressor to control the dynamics.
“To bring up the quiet part around 10dB, so that it competes with the yelling part.”
Think of the song “Let the bodies hit the floor” by Drowning Pool. He starts off with a whisper and builds into a scream, but you hear the whisper as well as you hear the scream. Not to say we don’t use volume automation as well to control dynamics and volume within the mix, but with the combination of both, we can really achieve the control we are looking for. Compression can also change the feel or the punch of an instrument or sound. I will give an example.. Why would we use compression on a triggered kick drum? It is a single sample that has the exact same sound and dynamics no matter how many times it is used. We don’t need to control the dynamics if there is no difference in dynamics. Well, we may use it to change the attack, sustain or just the feel of how it pockets into the mix. Again, it can take a lifetime of playing around with compression to see how they sound, change the feel and control the dynamics the way you want it to.
There really is only one difference between limiting and compression. The point in which it starts to work! “The Ratio” Limiting starts at a ratio of 4 to 1 and can go as high as infinity to 1, but 20 to 1 is what most of the limiters will go up to. The reason it starts at 4 to 1 is that true N.A.B “National Association of Broadcasters” zero level is +4dBu. Simply stated, anything that goes above our zero level on the VU meter is really starting at 4dBu.
We use limiting to control the peak activity or the “transient” sound. A kick drum is a very transient sound for example. It is very abrupt and has a large dynamic range, so if I have the drummer hit the drum while I set the input level and I bring the average kick drum level to around -5dB to 0dB on the VU meter and every once in a while the drummer hits it with a little more power and it causes the VU meter to pin or clip. This is the point I would use a limiter to control the peak activity that goes above the zero mark on the VU.
“To control the overages above N.A.B zero level.”
I want the kick drum with every hit to be consistently hitting between that -5dB and 0dB mark on the VU Meter, so I will use the limiter to assure that the peak overages are caught by the limiter and brought back down to 0dB.
I know this is a brief explanation to compression and limiting, but here at Pinnacle College we give ample time to hone in on your skills from the science side as well as the artistic/application side.