Compressors, Limiters, Noise gates and Expanders

There are several effects which deal with the manipulation of the dynamic range of an audio signal such as compression, expansion, limiter and noise gate. These effects work in similar ways to improve the quality of audio.

Compressors and limiters

Compression is the effect that controls a signal and prevents it from going over certain barriers (as this may cause distortion) by reducing the dynamic range of an audio signal.

There are two devices that give this effect: the compressor and the limiter.

A compressor usually comes in the form of a foot pedal which can also be used to prolong the sound.

A compressor increases the period of time in which a sound is heard by amplifying a sound until the intensity drops below a certain level. The ratio control determines the amount of gain reduction.

For example, if you set a ratio of 4:1 you will actually set the compressor to reduce an input level of 4 dB to an output level of 1 dB.

Another controllable setting is the attack of a compressor which determines the speed of the compressor responses and changes in the input level and the release which tells the compressor how fast it should return to no gain reduction. If a compressor is not set properly, however, it can change the sound in quite noticeable ways.

A limiter is actually a compressor which prevents the sound from exceeding certain limits. This is done gradually as clipping can cause distortion.

A limiter controls the amplification of a sound, reducing it in the case of signals exceeding the set barriers. The effect it generates is also called compression.

The limiter has a stronger ratio than the compressor and a faster attack time. There is no clear limit between a compressor and a limiter.

Most engineers agree that a device with a ratio bigger than 10:1 is rather a limiter than a compressor. However, the processes used in limiting and compression are exactly the same.


Expansion is the opposite of compression. This is used to expand the dynamic range of a signal.

A signal is processed when it falls below a certain preset limit and an expander will increase the dynamic range of the signal.

As long as the signal reduces the expander will act as a booster increasing it. However, when the signal level falls beneath a threshold level the expander acts like a noise gate.

Noise gates

The noise gate is a switch which automatically cuts off the signal when it falls under a certain level. Under this level the sound is actually considered noise and you wouldn’t want that in your recordings or, especially if used in combination with other -noisy- effects, on stage.

So, in order to eliminate this noise, you have to option of set the expander to act as a noise gate under a certain level.

Dynamic processing for the electric violin

Compressors and limiters are not used with violins very often. They were initially meant for guitars and guitar players to sustain the sounds and make them sound more like… violins.

Thus, if you are looking for a compressor/limiter for your violins you should try searching in places meant for guitar players. For more information on compressors and noise gates you should visit Active Musician.