Dynamic compression for beginners

Dynamic compression for beginners

Dynamic compression is a vital tool for audio work. It is important to understand the basic functions of a compressor to avoid affecting the general quality of your recording.


Basic Principle

The compressor reduces the dynamic range namely the difference between the lowest and the highest levels of an audio track. The highest levels are compressed by reducing the highest peaks and smoothing out the signal. There are multiple advantages:  to increase the gain of the track for more presence without saturating the mix, to produce a more natural and intelligible audio track, to deliver more impact and punch with percussive elements or to change the color and timbre of the sound.

Uncompressed audio signal

Uncompressed audio signal

Compressed audio signal

Compressed audio signal

 

Settings and Adjustments

There are several basic parameters in a compressor with additional settings on some devices.

  • Threshold: this is the level at which the compressor starts working, and is expressed in decibels (dB). Portions of the signal below this threshold will not be affected by the compressor.
  • Ratio: When the noise level exceeds the previously set threshold, the compression will act to mitigate it. The ratio determines the level of signal reduction above the threshold. This is expressed as a ratio x:y. A ratio of 2:1 means that a signal exceeding the threshold by 2 dB will be reduced by 1 dB above the threshold, and if a signal exceeds the threshold by 8 dB, it will respectively be reduced by 4 dB above the threshold.

These two parameters determine the amount of compression applied to the signal: the lower you set the threshold, the more the compressor processes the signal and the higher the ratio, the greater the compression is applied to the signal exceeding the threshold. When you set the threshold to inifinity:1, the compressor becomes a limiter: the output signal never exceeds the threshold regardless of the input level.

  • Attack: This is the time it takes for the compressor to react after detecting the threshold has exceeded, and is expressed in milliseconds.
  • Release: This is the time required to for the compressor to stop its actions once the signal no longer exceeds the threshold.

These parameters are set according to the nature of the signal; in fact they will have a significant impact on the timbre, including the transients, which are the periods during which a sound appears on or off.
With an attack phase too short, the compressor will tend to clip the transient and distort the original signal. Conversely if the attack phase is too long, the compressor will react too late. If the release phase is set too long, the compressor will still be active and the next attack will be subjected to an attenuation that may not necessarily be desired. If the setting is too short, it will cause a ‘pump effect’ which is sometimes favored by the sound engineer. It’s up to your ear to do the job!

  • Make-up gain: is simply an output gain adjustment to compensate for the drop in level due to compression.

The compressor makes it possible to expand and create consistency to the signal, to emphasize or minimize details and to homogenize the mix. It can also be used creatively to produce audible effects.


Find all our compressors in different formats:

Author’s gravatar
Lawrence started playing the electric guitar because of his passion for rock music. Back in the day he played in a metal band, but now plays more for himself.

2 comments

    This was incredibly helpful, thanks for sharing!

    Happy to help Peter! Thanks for your feedback 🙂

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