The Home Studio Pt II
Drugs in the Army, Rolling Stone no. 21, November 1968 Photographic Print Buy at AllPosters.com
The Home Studio Pt. II By Michael Elsner The Compressor One of the biggest factors in the sound quality of your recording is the proper use of a compressor. The proper use of a compressor can make or break a recording, so in order to ‘demystify’ what those knobs on a compressor do, we’re going to go through each one individually.
Compressing a signal is a two step process. The first step in the process compresses the sound, much like what would happen to a soda can if you were to step on it. The second step raises the overall level. The first step of compression involves the ‘threshold,’ ‘ratio,’ ‘attack,’ and ‘release’ parameters, while the second step involves the ‘output gain’ parameter.
Let’s look at each of the 5 parameters that you’ll encounter when using a compressor. 1. Threshold – Measured in decibels (dB), it is simply the point at which the unit turns on. When the incoming signal level crosses over the threshold, the unit will turn on. 2. Ratio – The amount of compression. This is measured as a ratio (x:1). A simple description of this would be “for every ‘x’ dB of signal crossing over the threshold, only one dB will pass.”
For example, let’s say the threshold is set to -20dB and the incoming signal is peaking at 0dB. If we set the ratio to 2:1, then for every 2 dB of signal that crosses over the threshold (incoming signal), only 1 dB will pass (outgoing signal). In this case, the incoming signal is peaking at 20dB over the threshold, which means that 10dB will pass (20dB / 2 = 10dB) giving us an outgoing signal level of -10dB (we compressed the signal by 10 dB). If we take this same example, but increase the ratio to 4:1, then for every 4dB that crosses over the threshold, only 1dB will pass. Since we’re peaking at 20dB over the threshold, if we divide 20dB by 4 (a 4:1 ratio), we get 5dB. So, for this example, only 5dB will pass, which means that the outgoing signal from the compressor will now be peaking at -15dB (we compressed the signal by 15dB). 3. Attack – The amount of time it takes for the compressor to turn on after the incoming signal has crossed over the threshold. This is usually measured in milliseconds (ms). 4. Release – The time it takes for the compressor to turn off after the signal has crossed below the threshold. This is usually measured in seconds. Setting your attack and release times properly comes with patience and a lot of practice. Like most things in music, there are no hard and fast rules, it just depends on the effect that you’re going for. However, here are two things to be careful of. If the attack time is set too slow, you’ll get a ‘pumping’ sound where the compressor will not turn on fast enough to catch the peaks, but will compress the rest of the signal. If you set the release time too slow, the compressor will not shut off before the next peak crosses over the threshold, resulting in an over-compressed and lifeless sound. Ideally, you don’t want to ‘hear’ the compressor working as much as you want to ‘feel’ the compressor working. If you can hear the compression, then chances are that your attack and release times are not set properly.
5. Output Gain – This takes place after all the compression has been set and is simply the point where you raise the compressed signal up to a listenable level.
For example, most compressors give you a read out via LED lights or a VU meter on the amount of ‘gain reduction’ that is taking place. This gain reduction is simply the amount that you’re compressing the signal. If your gain reduction readout indicates that you’re compressing the sound by 6dB, then it’s a logical idea to raise the output gain by 6dB. I hope this sheds some light on how to use a compressor effectively. It’s better to know what those knobs are actually controlling instead of just turning random knobs and hoping for the best, although, that sometimes leads to some pretty creative sounds as well! Until next time, have fun creating and compressing!
If you dig this guitar driven article... you'll probably jive on this one too! The Home Studio PT 1
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