What is Stem?
In audio production, a stem is a group of audio sources mixed together. A single stem might exist in mono, stereo, or in multiple tracks for surround sound. In sound mixing for film, the preparation of stems is a common strategy to facilitate the final mix. Engineers bring the dialogue, music, and sound effects, called “D-M-E,” to the final mix as separate stems. They use the dialogue stem by itself when editing various scenes together to construct a trailer of the film. After this, some music and effects are mixed in to form a cohesive sequence.
Stem-mastering is a technique derived from stem mixing. Like in stem-mixing, engineers group the individual audio tracks together. This allows for independent control and signal processing of each stem. Engineers can manipulate them independently from each other. Even though mastering studios do not commonly practice it, it does have its proponents.
Stem mastering is mastering performed from submixes called stems. When you play all the stems simultaneously, they make up the entire mix. When stems are provided, the mastering has more control over the mix. Engineers typically use stem mastering for situations where productions have significant problems they can’t address in mixing or by conventional mastering. Sometimes a project needs cohesiveness that may not be possible due to possible due to various project restrictions. Additionally, stems may be required for some television/film applications. Stem mastering requires extra time and a different way of working, and for those reasons, it is more costly.
By using extreme limitations on a stereo mix, the trade-offs are loss of transient details, loss of transparency and mix detail, and midrange frequency buildup. This is way stem mastering has become increasingly widespread, since it provides the opportunity to use EQ, limiting, and compression without these trade-offs. The stem approach allows the mastering engineer the opportunity to make larger or smaller changes to separate mix elements before applying the final compression to the complete mix.
Stem-mixing is a technique of mixing audio material based on creating groups of audio tracks and processing them separately before combining them into a final master mix. People sometimes refer to stems as submixes, subgroups, or busses. The distinction between a stem and a separation is somewhat unclear. Some consider stem manipulation to be the same as separation mastering, although others consider stems to be sub-mixes and use them along with separation mastering. 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.
In stem mixing, producers group audio tracks that have features in common into stereo stems or tracks to allow for individual signal processing of each stem. You can group, EQ and compress the kick drum, bass, and toms differently from the stem containing the snare, cymbals and acoustic guitars in order to maintain transients and clarity. Likewise, the vocals, the guitars and the horns can each have their own stereo stem and processing during mastering.
Stem technique originated in the 1960s, with the introduction of mixing boards. They had the capability to assign individual inputs to sub-group faders and to work with each sub-group (stem mix) independently from the others. Engineers widely use this approach to control, process and manipulate entire groups of instruments. Also, to streamline and simplify the mixing process. Additionally, as each stem-bus usually has its own inserts, sends and returns, engineers can route the stem-mix (sub-mix) through its own signal processing chain, to achieve a different effect for each group of instruments. Music producers are utilizing a similar method with digital audio workstations (DAWs). In DAWs, engineers can digitally process and manipulate separate groups of audio tracks through discrete chains of plugins.