Dynamic processors and their common parameters: threshold, ratio, attack and release.

Hello! My name is Artyom Bisyarin. I am from Kiev, Ukraine. This lesson is for week 4 of Introduction To Music Production at Coursera.org, and it's about basic principles of dynamic processors.

Theoretical Background

The dynamic processor is a very widely used electronic device, and as every gizmo it must have an object to deal with, and know what, when and how to do it.

Dynamic processors deal with the amplitude of sound, it's the object.

Dynamic processors change amplitude in two basic ways. It is what they do, and they can make certain sounds: 1) quieter, 2) or louder. All these operations with amplitude are often used to change dynamic range (the distance between the quietest and loudest sounds).

Dynamic processors know when to change amplitude due to threshold parameter. It is set to an amplitude value crossing which the dynamic processor starts or stops doing something.

Dynamic processors know how to change amplitude through ratio, attack and release parameters. Ratio is a relationship between input and output amplitude characteristics; it tells a dynamic processor how dramatically your sound must be changed. Attack is how quickly a dynamic processor starts applying the ratio to the sound. Release is how quickly it stops applying the ratio to the sound.

Everything said above was quite abstract, but it helps to get the idea behind dynamic processors, and it's better to understand it before using an actual device or plugin. Now let's explore all these parameters in several types of dynamic processors.

The Primary Dynamic Processors

Compressor

This processor reduces dynamic range making loud sounds quieter or quiet sounds louder, or both. All compressors that I've seen in my life make loud sounds quieter. In this case their threshold parameter is set to sound level above which the devices begin reducing the level of loud sounds. Ratio determines the amount of gain reduction applied to signals over the set threshold (a ratio of 3:1 means that for every 3dB the input level increases, the output level will increase by only 1dB). Attack determines how fast a compressor will respond to signals above the threshold. Release sets the amount of time it takes for the gain to return to its
original level when the signal drops below the threshold level.

Expander

The device works opposite to compressor expanding dynamic range instead of reducing it. It just makes quiet sounds quieter. You tell the expander which sounds are quiet setting the threshold. All sounds below it are reduced in level. An expansion ratio of 1:3 means that if the input signal drops 1 dB below the threshold level, then the gain will be reduced so that the output is 3 dB below the threshold level. Attack determines how fast an expander responds to signals below the threshold. Release sets the amount of time it takes for the gain to return to its original level when the signal exceeds the threshold level.

Derivative Dynamic Processors

There are other dynamic processors that are modifications of the compressor or expander:

  • Limiter – is a compressor with a very high ratio, so sounds just can't get higher than the threshold
  • Maximizer – is a limiter with automatic output gain knob set to the possible maximum level; it is used to raise the loudness of audio material without the risk of clipping.
  • Noise gate – is an expander with a very high ratio, so all sounds below the threshold are inaudible

Conclusion

So, you've seen that threshold, ratio, attack and release parameters are used in all dynamic processors. They have different meaning depending on the context they are in. Sometimes you don't have access to all of them, because some of them could be set automatically. But they are in the heart of a dynamic processor anyway, and it's very helpful to remember that using any type of dynamic processors.

Thanks for your time reading and grading this!


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