GoKawiilSynchronisation and SMPTE timecode (time code)
This document is a description (mainly technical, but not requiring extensive prior knowledge) of the SMPTE time-code synchronization system, especially the Bi-Phase Mark "LTC" timecode sync tone which can be recorded onto the audio track of a video tape or onto an audio tape. Other time code variants, such as VITC time-code are also mentioned. Some supporting information on the related subjects of colour television standards and field sequences is included. There is also a concise description of the binary coded decimal (BCD) representation as used in the SMPTE (or EBU) timecode (time code) data word.
My original reason for exploring this subject technically was to develop a low cost MIDI tape sync unit, which was a frequent customer request, and a logical addition to our range of electronic music gadgets. Our Time Code tape sync unit, which supported SMPTE (including Drop Frame format) and MIDI Time Code, was called the TS1 and was for over a decade a successful and highly-respected product.
Synchronisation systems
When you require pieces of audio, video, or music technology equipment (eg. tape recorder and sequencer) to work together, you may need some means to make sure that they play in time with each other. This is called 'synchronisation' or 'synchronization', which gets shortened to 'sync' or even 'synch'.
A magnetic tape-recorder track is the region of the tape that is scanned by one recording head element. It can, for example, carry an audio signal, that is an electronic analogue of a stream of sound. In order to use an audio track to record sync information, the information must be encoded into an audio-compatible signal, called a sync tone. An audio tape track on which a sync tone has been recorded is called a 'stripe'. It is desirable that the synchronised devices can join in wherever you start up the sync tone, even if it is not at the beginning of the stripe; this is called 'chasing'. The SMPTE/EBU timecode standard defines the predominant internationally accepted standard for a sync tone and it allows devices to 'chase' or locate to a precise position.
In music technology applications, with equipment which is not timecode compatible, you may be able to use a tape sync unit by way of a tempo-relative stripe system. Examples of such systems are traditional FSK (Frequency Shift Key) and the Philip Rees proprietary FSKplus format.
The SMPTE/EBU timecode standard
Until the advent of video recording, there was mechanical sound to film synchronisation. This mainly relied on sprockets (a row of neat holes) in the film and in special sprocketed recording tape. Relative timing adjustments could be made by slipping sprocket holes. The same sprocket holes were used to maintain synchronisation. Video tape hasn't got any sprocket holes, so when video arrived an electronic equivalent was needed to take the place of mechanical methods of synchronisation.
In 1967, The US Society of Motion Picture and Television Engineers introduced that which we call SMPTE ("simpty") time code. The audio sync tone version of SMPTE is called linear or longitudinal time code or LTC. By the way, there are also versions of timecode which can be inserted into a video signal or sent via a MIDI connection.
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