What does a dynamic processor do? They make very subtle changes to a musical sound They inject depth, warmth and life into our mixes and bring out the subtle nuances of the parts. They alter the range in volume between the loudest and softest sound on a recording or amplified musical performance.
There are four main types of dynamic processors: 1) Compressors 2) Limiters 3) Gates 4) Expanders
VCA (voltage control amplifier) Depending on the volume of sound the VCA can be set to bring up or down the volume of signal. A VCA acts like someone who constantly controlling the fader on a mixing board for one particular sound. If a sound is too loud they turn it down, if a sound is too soft they turn it up. The advantage to a VCA is that it can act much faster and precisely than any human being and it can control the volume of several sounds simultaneously.
Dynamic Processors are generally patched in two ways: directly to the instrument using the channel insert on a mixing board
COMPRESSORS & LIMITERS Compressors and limiters are designed to turn the loudest part of a signal down. When the VCA senses that a signal is exceeding a certain level it acts on the signal and turns it down. A compressor is almost always used on vocals, bass and on instruments with wide dynamic ranges.
There are three main functions that compressor/limiters perform: they protect against overly loud sounds that can overdrive electronic circuitry and cause unwanted distortion. they even out sounds in the mix that tend to constantly change volume. they increase the overall volume of the sounds that we want in the mix thus improving the signal to noise ratio.
There are four controls that are common to all compressors/limiters: i) Threshold ii) Attack Time iii) Release Time iv) Ratio
i) THRESHOLD The threshold sets the volume (db) level at which the compressor will begin to recognize the signal. Once the signal surpasses this level it’s fate is determined by the setting of the other three dials. Therefore only sounds above a certain volume level are altered.
ii) ATTACK TIME The attack time controls the amount of time that it takes for a compressor to turn down a signal once it passes over the threshold. An attack time that is set too fast will turn down the transients causing certain important elements of the sound to be lost. One that is too slow will end up allowing unwanted sounds through.
Attack time settings: On a vocal track we usually adjust the attack time in order to make it high enough that the S’s and T’s are heard but low enough that they are not exaggerated. On a good compressor/limiter attack times can be set anywhere between 100 microseconds and 20 milliseconds.
iii) RELEASE TIME The release time sets the amount of time it takes for the compressor to “let go” (or turn the signal back up) once it falls below the threshold. Release times can vary anywhere between 5/100 of a second to as slow as two or three seconds. Longer release times of one second or more tend to produce the smoothest and most natural results. This varies depending on the tempo of the music.
iv) RATIO The ratio determines how much that a signal is turned down. The ratio is the comparison between the amount of signal that passes over the threshold and the actual volume of the signal that will be outputted from the compressor.
How is the dB output calculated? Example: Say that you set the compressors ratio at 3:1. If a sound exceeds the threshold by 3 dB you will actually only hear the sound as being 1dB above the threshold after it is compressed.
Solve the following question: If you have a sound that is 12 dB above the threshold with the 3:1 compression how loud will it be outputted from the compressor?
Answer ! The sound will be outputted at 4db above the threshold. Most compressors have an LED or VU meter to show how much gain reduction is taking place.
How are Limiters and Compressors different? Both perform basically the same function. The limiter is really just an extreme compressor. It can compress signals at a 100:1 ratio. Compressors perform at ratios between 1:1 and 10:1 Limiters perform at ratios from 10:1 and 100:1 (or higher)
EXPANDERS & GATES These are devices that are most commonly used when mixing down a recording Although gates are frequently used by musicians to eliminate noise in a live situation.
EXPANDERS Expanders work in a similar way to a compressor except they act on the signal that is below a set threshold is instead of above a threshold. Expanders are used to expand the dynamic range of a piece of music. Compressors make loud sounds softer. Expanders make soft sounds softer
Upward Expanders ? These days sound engineers are also making increasing use of upward expanders (or Volume Maximizers) in order to take loud sounds and make them even louder !
GATES A gate is an extreme version of an expander. They are used most often to eliminate noise in a track. Gates allow you to set a threshold that is just above the noise floor. Any sound below the threshold will be silent. Expanders are a little more effective because they allow for sounds to fade out a little more naturally. Gates sometimes cause fading out sounds to get clipped prematurely.
A summary of dynamic processors: Dynamic processors are a very powerful and essential tool in the studio. When used correctly they will lead to clean, slick, smooth and professional recordings. When used improperly they can lead to annoying,airy and noisy recordings. Learning to properly use a dynamic proccesor is one of the most poorly understood yet important skills in the modern recording studio and live sound mixing.