The dynamic processing of audio signals is certainly one of the most important aspects of modern music production. While many producers doing Home Recording know (or have read somewhere) that the effects of compressor, limiter and Leveler enlarge the loudness of a recording so often the question remains, what the difference is in dynamic processing.
The compressor is a device for processing the dynamics of an audio signal. First, a threshold is set and if the volume of the audio signal is louder than the threshold, the compressor automatically reduces the level. The strength of the compressor will operating from the threshold is determined by the ratio parameter.
For example, a ratio of 2:1 means that a volume increase of 2 dB of the audio signal may rise by only 1 dB in the output level. There are several other parameters that are used for controlling a compressor, such as attack and release.
The application of a compressor is mainly for smoothing out valleys and mountains, resulting in a recording to get a balanced volume. For live and broadcast sectors, compressors are indispensable. As part of the Loudness War , the use of compressors in music production and, above all, the efficiency has increased greatly. The modern use of a compressor is in most cases, significantly increases the loudness of the audio signal. Other applications would be the smoothing of vocal recordings to generate more sustain for guitar and bass.
Compression can also be used to avoid clashing. E.g. for EDM music the kick may clash with other sounds such as the bass. This can cause peaking. To avoid this, the kick drum is often wired as a trigger or side-chain to a compressor. Every time there is kick drum, it automatically lower the volume of other connected instruments. The instruments seemingly “duck” out of the way of the kick drum. This allows you to have a solid kick drum without compromising other parts of the track.
This effect for dynamic processing is also used to create a balanced audio signal. A Leveler acts like an automatic volume adjustment (Automatic Gain Control) over a greater period of time. Short peaks are to pass unhindered, so these effects are often used in combination with a limiter or compressor. The leveler adjusts the volume level of an audio signal to the peak.
Typical applications for levelers are in department stores.
The limiter is similar to the compressor however it is also an effects unit for processing the dynamics of an audio signal. Limiters and compressors are very similar, the primary difference is in the processing. In contrast to compressors, limiters work with a theoretical ratio of infinity: 1 (often found in practice, values for the parameter ratio of 20:1 to 1000:1). This means that from the set threshold, the signal at the output can not be louder.
The idea behind a limiter is to set a maximum value for the level and keep the processed audio signal from being louder than this. Of course there is also a limiter attack (time), in which the signal passes through unhindered. Expensive limiters, which are used for in-ear monitoring, broadcast and large PA systems, have tolerances of less than one microsecond. These limiters are commonly referred to as the “brickwall limiter”.
So if you don’t want to exceed a certain maximum value or the RMS value, a limiter would be preferred.