Several inSync readers have asked some variation on the question of what the difference between a compressor, a limiter, and a leveler is.
For the sake of this discussion we will assume that you know the basics of what a compressor is and what it does. If not please see WFTD archive “compressor” to find out more.
A limiter (see WFTD archive “limiter“) is a device designed specifically to prevent audio levels from going higher than a specified point. In practice a limiter is basically a compressor with a very high compression ratio (20:1 to infiniti:1). The idea is that once the level reaches a certain point, the limiter will not let it go beyond that. Obviously there are tolerances such as a limiter’s attack time that will have some effect on its ability to precisely carry out this function. Some of the more expensive units offer guarantees that no matter what happens on the input the output will not go beyond what you set, even for a micro-second. These strict tolerances can be very critical for people in the broadcast industry, large PA system installations, touring PA systems, and perhaps most importantly, in ear monitoring systems.
A leveler (see WFTD Leveler) acts a little bit like a compressor in that it uses a gain cell to change the level of audio signals it is processing. Unlike a compressor which typically only lowers the level of signals above its threshold, a leveler acts as a sort of automatic level control and will increase or decrease the level of program material to maintain a consistent volume over time. These devices do not usually need to generate rapid changes in a signal like a compressor or limiter, but will change the material gradually over a specified period of time in order to achieve a near constant output level. As such, peaks of a short duration will get through as though no device was in line so it may also be necessary to use a compressor or limiter in conjunction with a leveler. Some levelers have these functions built in. Applications for leveling include music playback systems like in a store or office, theater PA systems, and tape duplication.