Timecode and synchronisation technologies exist to help the transfer and synchronisation of sound and moving pictures located on different recording, playback and editing technologies. In a world where many different sound and picture recording technologies exist, an understanding of timecode and synchronisation is an essential skill for the video and TV film maker and sound/music recordist.
For example, you may need to synchronise music and sound effects to on-screen action or synchronise an analogue multitrack tape recorder and an audio sequencer (such as a Cubase or Logic system).
This article focuses on the use of SMPTE timecode.
You can read about digital audio synchronisation (word clock) here.
NOTE: There are also devices known as Synchronisers which enable the transports of 2 or more multitrack tape recorders to lock together so they can function as one device. These are NOT discussed here.
The video maker needs to know ...
A music recordist needs to know ...
In the 1950s US television engineers realised that the hit and miss process of post production audio dubbing (re-recording speech, and adding sound FX and music to video and film) would be much easier if it could be automated using some kind of time/clock based synchronisation system. Their union, the Society of Motion Picture & Television Engineers (SMPTE) financed the development of a new technology called SMPTE ("simpty") timecode.
SMPTE timecode is now used in film, TV, video and music production and "versions" of it appear embedded in digital video formats such as DV, and the MIDI language (MTC).
Here is a list of the most common uses of SMPTE ...
The SMPTE timecode is an hybrid computer/audio signal (more on this later) which can be recorded onto ...
The SMPTE timecode signal carries Clock information in the form of hours, minutes, seconds and frames. Here is an example of a SMPTE display showing timing information ...
SMPTE timecode allows each individual picture (or frame) of film or video to have its own unique identifying number. There are 4 SMPTE frame rates for the four worldwide TV broadcast and film frame rate standards each identified by its unique fps (frames per second) rate ...
The SMPTE timecode signal is generated (and read back) by a SMPTE timecode generating device. Examples of SMPTE timecode devices include ...
Stand alone devices Film production uses these to feed an identical SMPTE timecode signal simultaneously to both cameras and audio recorders on location
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Devices built into cameras and camcorders
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Interface devices (sometimes stand alone, sometimes PCI video cards) which are plugged into a computer system and controlled by software.
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All SMPTE devices will generally have ...
A SMPTE timecode device must be able to both stripe (create/write/record) and read back a SMPTE timecode signal.
Within a SMPTE device, the SMPTE timecode signal is in digital computer signal form (i.e. a very quiet pulse wave). Before it can be sent to be recorded by an audio recording device (camera, tape recorder etc) it must be amplified to the volume of an audible line level audio signal. In this form the SMPTE signal is unpleasant to listen to, making a sound that will be familiar to anyone who has loaded games programs from a cassette player into their Commodore 64 or Spectrum ZX80 home computer. Essentially the signal is a "digital" line level audio signal!
Once recorded, the SMPTE signal can be replayed and sent back to the SMPTE device, which will have been reset from "write" to "read" mode. The signal enters the SMPTE device at line level and is then "modulated" back down to digital computer signal level before re-entering the software environment.
Physically therefore, the SMPTE timecode signal will exist in 3 forms ...
Click here for more on the different types of pulse wave.
SMPTE has been so successful in the TV and film industries that its principal concepts have been adopted for associated other industry technologies.
The DV (Digital Video) format includes an embedded timecode track that works exactly like SMPTE. There are 2 frame rates for NTSC (29.97fps) and PAL (25fps). DV timecode is used to automate batch capture (transfer) of clips from a DV camcorder to a computer editing system and to create EDL's for online/offline workflow's.
The process of using DV timecode is simple. The code is recorded along with pictures and sound to the DV tape during filming. Later during editing, when the camcorder is connected to a computer system, software on the computer reads the timecode and allows an editor to mark timecode "in" and "out" points for all the clips to be included in the edit. The software can then batch capture all the clips to the computer hard drive in preparation for editing. All through the editing process the timecode is used as a reference by the software to identify where edits, effects and transitions are made. Click here to read more.
SMPTE was adopted by the music business in the late 1970s to aid the synchronisation of multitrack tape recorders, sequencers and drum machines and in 1989 a "flavour" of SMPTE called MIDI TimeCode (MTC) was added to the MIDI specification to allow MIDI devices (computers, drum machines etc) to be inter grated seamlessly into the synchronisation process.
The process of synchronising music technologies with SMPTE and MIDI is discussed in-depth later on this page.
Music synchronisation is the process of getting musical events recorded on two separate recording devices (such as audio tracks on a multitrack tape recorder and MIDI events on a sequencer) to play together in time.
Music recordists must understand the basic principals of ...
The most commonly followed process for using both SMPTE and MTC in a music production situation is ...
The other common system involves connecting a MIDI cable between 2 MIDI devices (typically a sequencer and drum machine) and setting one to synchronise with the other by the exchange of MTC.
These 2 processes will now be discussed in-depth ...
In a situation where one device is controlling another via timecode, the controlling device is said to be the master and the other the slave.
In order for synchronisation to take place a slave device needs to know ...
In music production 3 timecode types are used ...
MTC and MIDI Sync/Clock timecode's may be generated by a suitably equipped MIDI device such as a sequencer, drum machine or combined SMPTE/MIDI timecode device.
SMPTE is usually generated using a SMPTE device (already discussed opposite).
Frame rates have already been discussed (opposite).
NOTE: It is not necessary to choose a particular SMPTE and MTC frame rate in music production unless it is being created for film and video but, by convention, recording studios use the prevailing geographical frame rate. Studios in London will use 25fps whilst those in New York will use 29.97fps.
As the code is generated by the SMPTE device it will be sent from the SMPTE device's audio output. This code can be recorded to an audio track of multitrack tape recorder, a process known as "Striping" or "Writing" the code.
During striping several procedures must be followed ...
Once the SMPTE code has been recorded to a tape track, and the tape rewound, the SMPTE device is set to "read" and the SMPTE signal fed back to its input. It will then read, or "lock up" to, the incoming code and and show it on its display.
Offsets (start-times) If a tape has been striped with SMPTE from beginning to end, and will have several individual songs recorded to it one after another, it will be necessary to set the SMPTE device to start at different locations along the tape. Before reading begins, the SMPTE device may therefore be programmed with an offset. For example a 30 minute tape containing 6 pop songs may require the following offsets to be set:
Song 1, 00:00:05:00
Song 2, 00:05:00:00
Song 3, 00:10:00:00
Song 4, 00:15:00:00
Song 5, 00:20:00:00
Song 6, 00:25:00:00
Note that even the first song has an offset (of 5 seconds) to ensure a glitch free start.
Because SMPTE is an audio signal it cannot be sent directly from a multitrack tape recorder to a MIDI device such as a computer sequencer but must first be converted into a digital signal such as MTC.
Developed in 1989, MTC is MIDIs version of SMPTE. It is identical to SMPTE except that it is a digital MIDI signal rather than an audio one. A SMPTE/MIDI device such as the XRI can achieve this.
A slave device (such as a computer sequencer) receiving MTC from a SMPTE/MIDI device (which is itself receiving SMPTE from a multitrack tape recorder) will therefore be told the position of the multitrack many times a second (depending on the frame rate).
The slave device can be set to commence playback from any point in the code and at any time signature and tempo. Therefore the slave device will need to be programmed with ...
MIDI Sync/Clock dates from MIDIs inception in 1984. MIDI devices built between 1984-89 (such as a 909 drum machine) will only understand MIDI Sync and ignore MTC.
MIDI Sync/Clock is NOT a clock signal. It consists of "dumb" pulses sent 24 times per beat (or quarter note). The speed with which these pulses are sent will determine the playback speed of the slave device. Therefore the SMPTE to MIDI Sync/Clock converting device (XRI) will need to be programmed with ...
If SMPTE has been recorded to a tape track the tape box and track sheets should contain the following information ...