Stem

A stem is an isolated element of a mix. For example, the dialogue stem contains the mixed dialogue portion of a complete soundtrack. The most common separation for stems is dialogue, music, and effects, and these stems need to be combined to make a complete soundtrack. On newer, more complex mixes, the effects stem is sometimes broken down further into effects, backgrounds, and Foley. For any release format, mono to SDDS® 7.1, individual stems will have been created in that format (i.e. 5.1 dialogue, 5.1 music, 5.1 effects).

Sound for picture is mixed in stems to help facilitate the mixing process. Edits, updates, and corrections can be more easily executed if the mixer only has to correct and match a particular stem as opposed to the complete mix. Stems are also an essential tool for creating a foreign track; the dialogue stem can be replaced with an alternate language, leaving the music and effects stems available for all subsequent foreign language dubs.

While the practice of mixing in stems has been around since the days of mono optical mixing, it is not uncommon for the stems of older films to have been lost, with only complete mixes (known as composite tracks or “comps”) surviving in the archives.