Compressors work by setting a ratio: 2 to 1, 4 to 1, etc. What that means is with a 4 to 1 ratio the compressor only lets its audio output rise 1db for each 4db rise at the input. It’s “compressing” the dynamic range of the audio. The threshold adjustment on the compressor sets the point where the compressor starts to operate. For instance, a threshold of -40db means the compressor acts on any sound over -40. That would add a lot of compression compared to -10 which would require louder audio before triggering the compressor.
Other common adjustments are attack and release. Attack sets how quickly the compressor starts when seeing audio over the threshold. Release is how quickly the compressor stops compressing after audio drops beneath the threshold. All these controls interact so setting them can be somewhat of an art.
I’d suggest starting with a ratio of 3 or 4 and experiment with different settings for the threshold. Leave the attack & release at their defaults to start. Listen carefully to the audio as there will be a point where you start to “hear” the compressor. The audio sounds crushed. This is generally not good. Raise the threshold or lower the ratio.
If you watch your meters, you’ll probably see less of a swing from softest sound to loudest. That the compressor working. At times it’s necessary to add output gain because as the compressor works it may lower the apparent audio level. If you Google, “using an audio compressor” a bunch of advice will pop up. Be aware that there are new Congressional guidelines governing how loud commercials can be.
Final Cut has a compressor in its audio plugins. It can work well, but its controls aren’t the best. Pro Tools comes with compressors, too. You’ll find them in the Dynamics category.
John
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