Signal Processing 101: An Introduction to Dynamic Effects
Also Known as serial effects for the way in which they are placed in series in the signal chain dynamic effects deal with amplitude across the whole, or a just a portion of the frequency spectrum of an audio signal. Dynamic effects include: compression, limiters, multiband compression, gates, duckers, and equalizers.
Compressors are devices designed to wrangle in the dynamic range of an audio signal to smooth them out and make them more consistent. This is done by setting a threshold for the device to turn on, meaning that once the audio signal reaches a certain level (threshold) the device engages and will only allow a ratio of that signal above the threshold. A typical ratio I go for when tracking vocals is about 3:1. That means that the compressor will only allow 1db of signal for every 3db that surpasses the threshold. If I set my threshold at -12db and a singers vocal levels are consistently hitting between -3db and -6db the result will be a more consistent level hovering around -10db. Attack and Release are settings for most compressor dealing with the amount of time, usually in milliseconds, a compressor will engage or disengage. The contour of transients can be easily manipulated using these functions. The final process of the compressor is the make up gain. Because the compressor significantly reduces the audio signal it must be boosted again to a normal level. So by using adequate make up gain you can compress an audio signal but make it seem much louder than if you had not compressed the signal.
Limiters are compressors that have much higher ratios. Typically 10:1 or 20:1 meaning that once an audio signal reaches a threshold it is barely allowed past. Limiters with rations up to 20:1 are often referred to as “Brick Wall” limiters and their sole intent is to prevent clipping to tape or overloading amps and loudspeakers. The functions of both compressors and limiters are the same for outboard rackmounted devices as well as plugin devices in your digital audio workstation (DAW).
Gates as well as expanders can be thought of as the opposite of compressors and limiters. Instead of narrowing the dynamic range of a signal they expand it by amplifying what reaches a threshold and attenuating the signal that does not. Gates are great for eliminating unwanted noise in an audio signal and are particularly handy for eliminating the hum of a guitar amp.
Graphic EQs are most likely going to be the most familiar to someone new to pro audio processing equipment as EQs can be found on most home and car stereos. Graphic EQs simply boost or cut audio signals with in fixed frequency bands.
Semi-parametric EQs have the ability to select variable frequencies to boost or cut, in the case of a fully-paramentric EQs the additional element of “Q” is added. Q represents the bandwidth of the frequency selected. A lower Q will result in a narrower band. A high Q will result in a wider band. Fully-parametric EQ’s are the prefered device for a “seek and destroy” EQ method.