A tool used to process audio, multiband compression is a function of dynamic range compression (DRC), which is also called compression. Most commonly, compression is used to control the loudness of the loudest sounds in an audio recording. A multiband compressor can be hardware or software. In audio engineering, a band is a frequency range, so a multiband compression controls multiple ranges of frequencies. Multiband compression is usually used by professional recording artists and sound engineers while mixing and mastering audio.
In mixing, using multiband compression can help give an audio recording more clarity. When two instruments play within the same frequency range at the same time, the result can be a muddy, unclear sound. A multiband compressor allows an engineer to amplify or decrease the volume of specific sets of frequencies, minimizing unwanted frequencies in the final track. Engineers adjust these levels using hardware and software multiband compressors.
When a song is mixed, the levels of individual audio tracks within each song are balanced by a sound mixing engineer. She is also responsible for mixing and adjusting sound frequency levels within the song to minimize clashing frequencies, creating a more clear sound. The mastering engineer is responsible for balancing audio for the whole of an album, ensuring that the tracks form a cohesive album sound with no major differences in track volume. During the mastering process, the engineer may use multiband compression to make minor final changes to the overall sound of the album.
Compression narrows the dynamic range of the audio by making the difference between the loudest sounds and the quietest sounds smaller. While most dedicated professional audio studios use hardware multiband compressors, multiband compression programs come readily available in plug-in form for use on audio editing and recording programs like Pro Tools®, Cubase® and Audacity®. Types of compressors include limiters, sidechains, parallel compressors, and multiband compressors.
When the intensity or volume of a sound frequency is out of proportion with the intensity of other sound frequencies, whether in live sound or in an audio recording, multiband compression can be used to apply compression to specific sound frequencies, dampening them. Both hardware and software multiband compressors feature controls that allow the user to select an audio frequency range and change the intensity for that range of frequencies. Multiband compressors should be used with subtle care. Compression overuse can create a tin-can telephone sound, and improperly adjusting sound frequencies can make the recording muddier than the original.