In audio production, a stem is a group of audio sources mixed together, usually by one person, to be dealt with downstream as one unit. Even though it is not commonly practiced by mastering studios, it does have its proponents. The reason for this is to leave more space in the mix to make the mastered version sound cleaner and louder. Most of the mastering engineers require music producers to have at least -3db headroom at each individual track before starting stem mastering process. Just as in stem-mixing, the individual audio tracks are grouped together, to allow for independent control and signal processing of each stem, and can be manipulated independently from each other. Stem-mastering is a technique derived from stem mixing. A similar method is also utilised with digital audio workstations (DAWs), where separate groups of audio tracks may be digitally processed and manipulated through discrete chains of plugins. Additionally, as each stem-bus usually has its own inserts, sends and returns, the stem-mix (sub-mix) can be routed independently through its own signal processing chain, to achieve a different effect for each group of instruments. The approach is widely used in recording studios to control, process and manipulate entire groups of instruments such as drums, strings, or backup vocals, in order to streamline and simplify the mixing process. The technique originated in the 1960s, with the introduction of mixing boards equipped with the capability to assign individual inputs to sub-group faders and to work with each sub-group (stem mix) independently from the others.

It depends on how many separate channels of input are available for mixing and/or at which stage they are on the way towards reducing them to a final stereo mix. Some consider stem manipulation to be the same as separation mastering, although others consider stems to be sub-mixes to be used along with separation mastering. The distinction between a stem and a separation is rather unclear. Stems are also sometimes referred to as submixes, subgroups, or buses.

Stem-mixing is a method of mixing audio material based on creating groups of audio tracks and processing them separately prior to combining them into a final master mix. Green arrows indicate group assign buttons. Image of group assign features on individual mix channels of a mixing console.

Mix and mastering programs