As humans, we have tons of built in “thresholds” surrounding all of our senses. What do you do when the shower gets too hot? As the temperature rises, it eventually gets to the point that your nerves tell your brain “ouch” and your brain tells you “too hot!” and you turn down the hot water. That point of “too hot,” be it 110 degrees or 120 degrees, is your skin’s personal threshold for water temperature. In the case of a compressor, the threshold control defines the point at which the compressor will begin to alter the dynamics of the signal, or compress. If the signal breaches the threshold or gets “too loud,” the compressor reacts by compressing or “turning down” the level of the output, just like you turning down the water temperature in the shower. In other words, It’s the threshold control that tells the compressor when to compress and when to leave the signal alone.
All dynamic processors work on the simple principle of a defined action resulting in a prescribed reaction. Think of it as an “if..then” statement of sorts; if the incoming signal level reaches “X” or higher, the processor will react in “Y” way, if the signal remains below X then do nothing. The threshold control in a dynamic processor allows us to define the reaction point, or the “if” part of the statement, setting the level at which the processor reacts, sometimes by reducing (compressing) or increasing (expanding) the level of the output.
I know what you’re thinking, you’ve seen that threshold control just sitting there, but the presets you pick automatically set for you, so what’s the big deal? Indeed, most compressor plug-in presets include a preset threshold value, and while it might be tempting to use that level, it is very important to understand that the preset threshold may not be affective for your specific compression task. If the threshold is set too deep, it might over compress the signal, removing all the dynamics. If the threshold is set too light, the compressor might not engage at all. Of course, sometimes you get lucky and everything works out, but remember, the preset has no way of knowing what your input level looks like or how much compression your signal needs. Until we have intelligent processors that can adjust their threshold automatically to accommodate the input signal, you will need to adjust the threshold control manually. Even if the processor could detect and adjust the threshold automatically based on the input signal, the preset couldn’t know how much compression you needed or desired, just like no one else would know just how hot you like your showers on any given day.
Ultimately, whether you set up your dynamic processors from scratch or from a preset, it is imperative that you understand and use the the threshold control to achieve the desired amount of processing. If you want to learn more and see some cool animations, watch the following free clip on understanding threshold from my new course lynda.com, Foundations of Audio: Compression and Dynamic Processing. Be sure to check out the entire course for more tips on using threshold and other compression controls.