Rhythm Creation - Music Production and Sound Reocording

One of the music signal processing effects that many people struggle to understand is the compressor, the reason they fail to understand it is because firstly with a compressor it is harder to hear the effect it is creating but also because they haven’t learnt why and what it is for, this quick tutorial will quickly explain what a compressor is and hopefully put some people on the right track.

What Does A Compressor Do?
Putting a sound through the compressor will make the loudest parts of a sound quieter, reducing the volume gap between the louder and quieter parts of a sound. If you could see the waveform of the sound you would see that it is flattening the peaks down closer to the troughs. It is basically an automatic volume fader.

When Should I Use It?
  1. Because the peaks of a sound are clipping (sending the volume into red) - compressing it will bring down these peaks and so no more clipping occurs and you will end up with a better behaved sound.
  2. Because you want to raise the quieter parts of a sound (such as the tail/sustain section of a sound) - A compressed sounds peaks are reduced and so therefore the overall volume of the sound can be pushed up via the output gain, in effect making the quieter parts of a sound louder. Because the sounds tail section is louder, it makes our ears perceive the whole sound as louder. (This technique can be used on the final mix to make the track loud). Advertisers also use this on TV adverts so the sound is much louder, so you can hear it when your in the kitchen making a brew.
  3. Because you want to emphasise the first part of a sound - Using the attack (see below) we can let the first part of a sound through uncompressed and then compress the rest of the sound. Making the sound more punchy.
How Do I Use It?
The best way I can explain this is to go through each part of a typical compressor and tell you what each one does. These individual parts should be available on most hardware and software compressors.

Compressor: Image from Stock Xchng (www.sxc.hu) User:sibaudio Threshold
This sets the volume level at which the compressor starts to do its compressing. Whenever the sound volume goes above the level of the threshold the sound will get compressed. Anytime the sound's volume is below the threshold the compressor is doing nothing and the sound will therefore stay at the same volume.

When the volume goes above the threshold it gets compressed and the ratio is by how much should it get compressed. 1/2 ratio is going to compress any volume above the threshold to 1/2 the amount above the threshold. For example if the threshold is 50dB and the sound going through the compressor is 70 dB. The sound will come out at 60dB. At 1/4 ratio it will come out at 55dB. 1/10 ratio will be 52dB.

This sets in milliseconds how fast the compressors reacts once the sound level goes above the threshold. Most of the time you will want to set this to a very low setting. As you set it higher more of the beginning of the sound will be let through after breaking the threshold. This allows you to place emphasis on these parts (commonly used on kicks to make them more punchy).

This sets the time that the compressor stops doing it’s compressing after the sound has dropped below the threshold, setting this too low can make the sound sound like it is pumping. Commonly used on dance style recordings as a wanted effect.

Not seen on all compressors, sometimes might be seen as a soft knee on/off button and on other compressors you can control it with a proper dial. The Knee is the time it takes for the compressor to reach the maximum ratio of compression once compression has started to set it. A soft knee will take more time to reach maximum compression.

Output Gain
This is where you can increase the overall volume after it has been through the compressor.

Common Mistakes
  1. Compressing a recorded sound can cause any noise, hum or unwanted sound in the background of the recording to become louder reducing the quality of the recording.
  2. Too much compression applied doesn’t sound good. Sometimes a pumping like effect can be heard which can sound dreadful on the wrong sort of music. There is also quite a backlash from some people saying that some modern music sounds dreadful and of less quality because it is so loud due to overuse of compression.
  3. Removing the ups and downs of music on recordings that don’t need it. You won’t hear very much if any compression at all on classical music because you want to keep the very quiet sounds quiet to give more feeling and flow to the music. Adding compression may ruin the feeling of the music in situations like this.
This should help you to use compressors easily and effectively, one last thing to think about is where in the effects chain you apply the compression. After or before reverb and delay effects can sound very different as your also raising the levels on those effects. So think about when you want the compression applied.

If anyone has anything to add or other ideas on how to use it, please add it to the comments.

Tutorial Written by Edward Cufaude for Rhythm Creation.

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