Longitidinal time code (LTC) is a timing signal that is part of an audio tape recording. It is recorded on a track that runs lengthwise along the tape, which is why it is called longitudinal.
LTC is one of two timing codes adopted by the Society of Motion Picture and Television Engineers ( SMPTE ) in the 1960s. The other, known as vertical interval time code ( VITC ), is used with video recordings.
LTC assigns a specific time in hours, minutes, and seconds to various points along the tape. The LTC can therefore be used to keep a playback machine synchronized with a master time source. This can be useful in broadcasting applications where program lengths and time-slot scheduling are critical. Because the timing signal is recorded lengthwise along the tape, it is necessary for the tape to be in motion for the signal to be read.