What are Stems?
A stem (short for STEreo Master) is an audio file that contains one or more instruments or sounds. Multiple stems (usually between 3 and 9) are summed together to create a master file. Therefore a song (or instrumental piece) is usually delivered as a “Stem Pack” (a collection of 3-9 stems).
Instruments can be grouped to form a stem in any way but normally this is done by instrument category. For example, it would be common for a pop/rock song to contain multiple guitar parts and therefore these can be grouped together as one stem.
What is the purpose of stems?
Stems have a number of uses:
In broadcast media (particularly trailers, promos, reality television and advertising) music is often supplied as stems to allow the editor more control of the music to sync with vision. Music for media is often sourced from production music libraries (aka library music or stock music) and increasingly their catalogue is available in stems.
In pop and electronic music it has become common to supply a mastering engineer with stems to allow more control of the mix/mastering process.
In film, the dialogue, music and effects audio are split into stems to allow some flexibility. For example, if the film is to be dubbed in to a different language, only the dialogue stem needs to be replaced, leaving the music and effects in place.
DJ’s perform music in stem format to allow them more flexibility and creative freedom when mixing music tracks.
Stems In Broadcast Media
The use of stems in broadcast media is becoming much more common and music libraries are moving towards delivering music tracks in this format as a standard.
Here are a few reasons why it is useful to work with stems:
Stems allow much more flexibility to customise the music to compliment the pictures. If you think of the way music tracks are traditionally delivered as a stereo file, what are the options to customise it? It can be edited (shortened or lengthened in duration); turned up or down in overall volume, or EQ’d to change the overall tone of the track (e.g. remove the bass or treble). However, if the track is supplied in stems, the user has the option to all of the above processes and the ability to adjust volume or remove particular instruments in the music. This can have a profound effect on the overall feel of the music in regards to mood, pace or texture.
By customising the stems, the music becomes unique to that production. There are many library/stock music tracks available but popular tracks get used often. Who wants to sound like everyone else?
Having stems allows the editor to create multiple versions of the same music track. In long-form media productions such as documentary and film, it can be effective to use the same music more than once to maintain consistency (as a film composer would with a score) but having stems will allow the editor to customise each version to create variation and maintain interest in the soundtrack.