A Brief History of SMPTE Time Code

What is SMPTE Time Code?

Adopted in the late 1960's by the Society of Motion Picture and Television Engineers, SMPTE (sem-tee) time code is an industry standard frame numbering system that assigns a specific number to each frame of video in the format of hours, minutes, seconds, and frames. There are two SMPTE formats for time code: Longitudinal Time Code (LTC) and Vertical Interval Time Code (VITC). LTC is an audible electronic digital signal recorded on an audio or time code channel of a VCR or audio recorder. VITC is a visual frame identification code recorded in the vertical blanking interval of each video field. VITC time code must be recorded at the same time as the video and it can be read in VCR pause mode. LTC time code offers more flexibility than VITC time code in that it may be recorded prior to recording the video (prestriped), during production, or added to the tape at a later time (post striped). However, it can use up an audio channel and the tape must be moving in order to read it.

Why is SMPTE time code so important? The answer can be stated in two words: accuracy and repeatability. With SMPTE time code, every frame of video is given its own unique identifying number. Once recorded, that time code/video frame relationship will be the same every time the tape is played.


Types of Time Code Equipment

SMPTE time code equipment generally falls into one of four categories: generators, readers, character inserters (or window dub inserters) and translators.  The time code generator creates the time code signal. Time code readers "read" the electronic time code signal, decode it, and display it. The display may be an LED readout or be superimposed over the video picture ("window"). Window inserters are generally used to produce work copies of the master tape with the time code display "burned" into the video picture. Other time code based "window dubs" equipment fills a variety of needs. Translators allow the user to change between LTC and VITC or into RS422 and RS232 protocols to communicate time code information to VTRs, edit controllers, and computers. A GPI uses time code to electronically trigger events in production, playback, scientific experiments, etc.


HORITA Time Code Products

HORITA offers a wide range of SMPTE LTC and VITC generators, readers, window inserters and translators. Our LTC line offers choice and flexibility, from the basic WG-50 play speed reader/window inserter to the complete TRG-50 PC generator, search speed reader, window inserter with RS232 interface and TC-TOOLKIT™ tape logging software. HORITA's VITC products provide generator, reader/window inserter, and translator functions so the user may translate between LTC and VITC, as well as have a full function VITC system. LED units such as the TCD-100 and VLR-100 provide visual displays as well as reader/generator functions. The TCI-50 and RLT-50 allow time code to be inserted into or extracted from an RS422 data stream. The GPI-50 is a dual time code comparator general purpose interface.

A complete studio clock and time code system is available with the HORITA GPS-MTG. The system uses the accuracy of the atomic clocks in the Global Positioning System and generates time of day, time zone, and date SMPTE time code. Compatible LED and video overlay display units show time of day and date for any time zone. When the studio time code is needed in the field, the PG2100, a palm sized, battery operated, mini time code generator, can be set to the GPS-MTG SMPTE output, providing multiple field cameras with precise time/date time code, in step with each other and with the studio/field master.