Stems can refer to two things in music: music notation and audio production.
Stems are the lines which extend from the notehead. Stems may point up or down. Different-facing stems indicate the voice for polyphonic music written on the same staff. For single-note melodies, the stems usually point down for notes on the middle line or higher, and up for those below. If the stem points up from a notehead, the stem originates from the right-hand side of the note, but if it points down, it originates from the left. There is an exception to this rule: if a chord contains a second, the stem runs between the two notes with the higher being placed on the right of the stem and the lower on the left. If the chord contains an odd numbered cluster of notes a second apart (such as C, D, E), the outer two will be on the correct side of the stem, while the middle note will be on the wrong side.
The length of a stem is usually that of an octave on the staff, going to either an octave higher or lower than the notehead, depending on which way the stem is pointing. If a note head is on a ledger line more than an octave away from the middle line of a staff, the stem will be elongated to touch the middle line.
In any polyphonic music in which two parts are written on the same staff, stems are typically shortened to keep the music visually centered upon the staff.
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.
In music mixing for recordings and for live sound, stems are subgroups of similar sound sources. When a large project uses more than one person mixing, stems can facilitate the job of the final mix engineer. Such stems may consist of all of the string instruments, a full orchestra, just background vocals, only the percussion instruments, a single drum set, or any other grouping that may ease the task of the final mix. Stems prepared in this fashion may be blended together later in time, as for a recording project or for consumer listening, or they may be mixed simultaneously, as in a live sound performance with multiple elements. For instance, when Barbra Streisand toured in 2006 and 2007, the audio production crew used three people to run three mixing consoles: one to mix strings, one to mix brass, reeds and percussion, and one under main engineer Bruce Jackson's control out in the audience, containing Streisand's microphone inputs and stems from the other two consoles.
Stems may be supplied to a musician in the recording studio so that the musician can adjust a headphones monitor mix by varying the levels of other instruments and vocals relative to the musician's own input. Stems may also be delivered to the consumer so they can listen to a piece of music with a custom blend of the separate elements. (See List of musical works released in a stem format.)
See also 
- Hollyn, Norman (2009). The Film Editing Room Handbook: How to Tame the Chaos of the Editing Room (4 ed.). Peachpit Press. pp. 162, 186, 269. ISBN 0321679520.
- Tozer, Edwin Paul J. (2004). Broadcast Engineer's Reference Book. Taylor & Francis. p. 615. ISBN 0240519086.
- LoBrutto, Vincent (1994). Sound-On-Film: Interviews With Creators of Film Sound (2 ed.). Greenwood. p. 183. ISBN 0275944433.
- Woodhall, Woody (2010). Audio Production and Postproduction. Jones & Bartlett. pp. 461–462. ISBN 1449603203.
- Bennett, Stephen (October 2005). "Stem Mixing In Logic". Sound On Sound.
- "Studio Legend Bruce Jackson Chooses VENUE and Pro Tools for Streisand World Tour". Digidesign press release. CreativeCow.net. 6 February 2007. Retrieved 8 February 2011.
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