Wednesday, February 1, 2012
Compression 101 - In Plain Words
Hey friends. I recently got the chance to do some compression tests. I really wanted to see what the compressor was doing to the digital waveform in order to explain it better to others and just to reinforce my understanding of compression. You can never really say you know it all - you're always going to learn new things.
Compression is sort of a mystical topic for many people. They don't really know what it does, or they kind of hear it, or they don't really know how to not abuse it. It's a delicate tool but it's certainly our most important tool for manipulating dynamics, feel, and punch. So let's break it down into simple terms so we can see what compressors actually do.
Ratio - A ratio of X:1 - for every X decibels that comes in, only 1 decibel will come out. Increasing the ratio is like strengthening the compressor's clamping power. If you imagine a compressor as being a bungee cord - a lower ratio will be a looser cord, and a higher ratio would be a tighter cord that stretches less.
Attack time - When the audio passes BELOW the set threshold, this is the time it takes the compressor to reduce the sound to its calculated amount (based on the ratio). Adjusting this fast or slow changes the sound of the "attacks" of the notes - but almost in reverse. A fast attack comp setting will chop off the front of a snare hit. A slow attack comp setting will let the hit pass, and compress what's after the hit.
Release Time - once the audio passes ABOVE the threshold, this is the time it takes the compressor to return to original (unprocessed) volume. The release really affects the sound of the sustain of the notes. A fast release will stop compressing, thereby returning the signal to normal volume, thereby raising the level of the sustain. A slow release will slowly release the gain reduction, meaning it stays quieter longer, meaning the sustain will be quieter.
Limiting / Saturation - These two types of compression are delicate matters. You can use them to your advantage to control dynamics without sounding like a compressor. If overused, both can seriously damage the sound. Look at the chart below for more info.
Aside from all other aspects these are the basic parts of a compressor, and you should learn to hear what they do. Let's put this information in two separate charts so you can really understand how these pieces of the puzzle interact.
CLICK THE PHOTOS TO ENLARGE. Use them, read them, enjoy them!
Compression - Attack / Release Times
Compression - Ratio / Compression Types