An acronym standing for the Society of Motion Picture and Television Engineers. In the context of electronic music, it nearly always refers to a standard developed by that body for a time synchronization code. This time code was once used to synchronize sequencers and drum machines with a tape being played back, as well as other uses such as syncing audio to video. There are several means of encoding the signal; all forms contain the same data, but the means of transmission is different. One relevant and unusual form consists of a modulated audio signal (in the manner of a computer modem) which can be recorded and played back by an audio recording device.
The time code is a stream of data containing time values and "ticks" which precisely denote a particular time. The SMPTE code does not tell the time of day; rather, it tells time starting from an arbitrary zero time. Typically, at the start of an audio recording session employing multi-track tape, one track of the tape is "striped" with a pre-recorded or generated SMPTE audio signal. This marks time throughout the tape. Subsequent audio signals are recorded on other tracks. When, for instance, it is necessary to synchronize a sequencer with the tape playback, the SMPTE signal is played back into an interface which converts it into whatever type of clock or synchronizing signal the sequencer accepts (see MIDI clock and MIDI time code). Once the sequencer is informed of what the SMPTE start time of the song is, it can cue itself up to match the tape position and then keep pace with the tape, even if the tape speed changes.
SMPTE time code divides time into hours, minutes, seconds, and frames. The last is a consequence of the fact that the SMPTE code is intended to facilitate the synchronization of audio to television or film projection. As a result, the standard allows for four possible values for the number of frames in a second: 24 (film rate), 25 (PAL television, the standard used in most of Europe), 30, and an oddball known as 30-drop which adapts to a peculiarity of the NTSC color television used in North America and Japan. If the audio is not required to synchronize to film or video, the choice is arbitrary; most users choose 25 or 30 when they have a choice. (30-drop is not recommended when it isn't required to synchronize to color NTSC video.)
The use of SMPTE synchronization is now decreasing as analog tape is declining as a recording medium. Hard disk recording does not need any time code, since the DAW software can embed the timing information in with the data on disk and provide synchronization to other devices via digital mechanisms such as MIDI or DIN sync. SMPTE is needed only when the DAW is required to synchronize with an analog medium, such as audio tape, video tape, or film.