Dynamic Range Processing

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reteo's picture
Dynamic Range Processing

When it comes to dynamic range processing, there are four tools that exist on a spectrum.  They are:

Limiter ---> Compressor ---> Raw Audio --> Expander --> Gate

The reason that they are in a spectrum is that they do essentially the same thing: They apply a ratio to incoming aplitude values, adjusting the output based on that ratio.  What this means is that for every x decibels in, y decibels go out.  In compression, the ratio is x:1.  In expansion, the ratio is 1:y.

The Limiter is at one end of the spectrum, and has an infinite ratio, essentialy *:1.  This means that it doesn't matter what amplitude value goes over the threshold, it will only increase the amplitude to that threshold, and no higher.  This is great for preventing clipping, although it can cause its own brand of distortion if the source is constantly hitting it.

The next step down is the compressor.  It has a finite ratio, such as 2:1.  This means that for every 2 decibels of amplitude over the threshold, only one decibel is increased in the output.  This is great for evening out a voice and removing variations in the volume levels based on head movement and breath levels.

The next step is unprocessed, which is an x:x ratio, meaning that there are no changes.  The best thing to record, because then processing can come later.

Now we go to expansion, the opposite of a compressor.  An expander uses a ratio of 1:y, meaning that for every level of amplitude going in, two are set outwards.  This can make things loud, except that, unlike the compressor, this works in a downward direction, meaning that it expands in the quieter direction.  The main use of expansion is to increase the distance between the signal (your voice) and the background noise.  The end result is that it quiets the noise without cutting off speech.

Finally, we reach the noise gate, which is to the expander what the limiter is to the compressor; it is an infinite expander; once the amplitude reaches a specific threshold, it is infinitely expanded, which people simplify by saying "shut off."

Well, hopefully, this helps those who are not yet clear on what the four tools do, and I apologize to those who find the whole thing a little muddying.