Stem mixing and mastering

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. Stems are also sometimes referred to as submixes, subgroups, or busses.

Some people consider stems the same as separation mastering although others consider stems to be sub-mixes to be used with separation mastering. There is some lack of clarity with regards to what is a stem versus what is a separation. Semantically it seems to depend on how many separate channels of input are available for mixing and/or at which stage they are towards reducing them down a final stereo mix, with different people drawing the separation line at different places.

This technique originated in the 1960s with the introduction of mixing boards that were equipped with abilities to assign individual inputs to sub-group faders and then manipulate each sub-group (stem mix) independently from the others. This technique 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. Additionally, as each stem-bus usually has its own inserts, sends and returns, the stem-mix (sub-mix) can be processed independently through its own signal processing chain to achieve a different effect for each group of instruments. This technique is also practiced with Digital audio workstations (DAWs) in a similar way where groups of audio tracks may be processed and manipulated digitally through a separate chain of plugins.

Stem-mastering is a technique derived from stem mixing. Just like 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. Even though this method is not commonly practiced by mastering studios it does have its proponents.

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. A single stem may be delivered in mono, stereo, or in multiple tracks for surround sound.

In sound mixing for film, the preparation of stems is a common stratagem to facilitate the final mix. Dialogue, music and sound effects, called "D-M-E", are brought to the final mix as separate stems. Using stem mixing, the dialogue can easily be replaced by a foreign language version, the effects can easily be adapted to different mono, stereo and surround systems, and the music can be changed to fit the desired emotional response. If the music and effects stems are sent to another production facility for foreign dialogue replacement, these non-dialogue stems are called "M&E". The dialogue stem is used 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.

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