Dynamic Processors – Threshold, Ratio, Attack and Release

Dynamic processors are effects used in the post-production/mixing stage of sound recording. They are designed to manipulate the dynamic range of recorded sound. This involves adjusting the quietest and loudest levels of the audio.

Dynamic Processors can either reduce dynamic range by the process of compression or increase dynamic range through the process of expansion.

Manual ways of processing the sound be done using by various techniques including manually isolating sections of the recording and manipulating gain – or by ‘riding the fader’ i.e. manually adjusting the fader volume throughout the performance in the DAW. This can be successful, but can also become cumbersome if you decide to further reduce the whole level of an individual track. This is where dynamic processors are useful as they can fully automate the process.

Compression

Compression means either making the loud audio quieter – or make the quiet audio louder. The end result is a decrease in the dynamic range. This means for music production purposes we have more consistency throughout the project. Examples include compressors and limiters.

Expanders

Expanders as the name implies are used to expand the dynamic range of a piece of audio. This means decreasing the levels of the quiet areas or increase the levels of the loud areas to making them louder. Examples include expanders and noise gates. Usually they are set up to decrease the quiet levels.

Compressors, limiters, expanders, and gates are nonlinear devices. They have a common set of parameters – threshold, attack, release and ratio – but with different rules.

All dynamic processors have one section that’s designed to analyze the input signal (the side chain section, or the key section), and one section that is the volume fader.

Parameters of Dynamic Processors

Threshold

This is the level at which the dynamic processor starts to function. If sound levels cross over the threshold point then they are processed and other parameters may kick into effect.

Compressors and limiters will process sound that goes above the threshold point. Expanders and gates will process sound that goes below the threshold point.

Threshold levels will always need to be adjusted –you can’t rely on a preset to set threshold as it is related to the underlying musical material.

Ratio

Ratio determines how much the level is affected once it crosses the threshold point. It is expressed in the form of Input:Output

At a ratio of 1:1 – for a signal level of 1dB over the threshold, 1dB will be outputted. This means that there is no change.

At a ratio of 2:1 — for a signal level 2 dB over the threshold, 1dB will be outputted. This means that the output will be halved.

As the ratio increases the level of compression increases. At a ratio of 10:1 — for a signal level 10 dB over the threshold, 1dB will be outputted. In the case of compression, this ratio or higher is considered to be a limiter. At a ratio of 30:1 — for a signal level 30 dB over the threshold, 1dB will be outputted. This stops the sound and is known as a brick wall limiter.

Attack

The level of attack is how quickly the volume fader kicks in once the signal has crossed the threshold. Attack is usually shown in milliseconds [ms]. The lower the attack rate, the faster the fader will move.  This controls the amount of the transient allowed through unaffected by the dynamic processor. A transient is an area of the sound where the amplitude changes greatly in a short amount of time.

Release

The level of release indicates how quickly the volume fader returns to normal once the signal has crossed back across the threshold. Release is also expressed in milliseconds [ms]. The lower the rate, the faster the fader will move.

Dynamic Processors and Audio Production

All of these dynamic processor parameters (threshold, ratio, attack and release) can be set up differently and this can have a major impact on the end result of the sound. And as they are all interrelated it can make things even more challenging. A tweak in one area can dramatically influence the others. Therefore as audio producers it is essential that we understand each component and the influence they can have on each other. And at the end of the day it is essential that we use these tools in a musical way – and help improve the audio, the mix and the music that we are helping to produce.