| Time code (master-slave) | |
| Time code systems generally have a single Master or time code source with all of the other devices referred to as ‘slaves’. |
| These slaves either (a) read the time code recorded on their tracks and adjust playback speed to keep locked to the master (continuous resynchronization) or (b) read the time code and start playing when a specified time is reached (trigger sync). | In either case, the slave is usually connected to (or has built in) a synchronizer. This device reads the incoming code and compares it to the code written on the slave’s tracks. The synchronizer searches for the correct spot (with fast forward or rewind) and then plays with variable speed until the slave code equals the master code. This is the moment when the two have ‘locked’ and there is usually some visual indication of this status on the slave or synchronizer. |
| Synchronizers allow the user to program an arbitrary ‘offset’ into the system so that the slave code need not bear any resemblance to the master code: for example you might want the slave to sync its location 01:20:39:15 to the master’s 01:22:39:15, etc. | It is important to note that most systems will not tolerate differences in time code type: always insure that all tapes are ‘striped’ or recorded with exactly the same frame rate and nondrop or drop type! |
| The act of recording or poor tape quality, etc. may
degrade the time code signal and make it difficult for the synchronizer
to differentiate pulses. A time code refresher is sometimes used
to amplify and alter the on/off slope of the pulses to reduce the amount
of errors. If the code disappears entirely the slave will stop unless
the system provides for ‘jam
sync’.
Jam sync refers to the synchronizer’s ability to take over generating code when the source stops. Of course the accuracy of the synchronization is in jeopardy because the new source is ‘freewheeling’ or independent of the actual code recorded - however if the drop out is for short period, jam syncing will work. Computers (usually functioning as sequencers or Digital Audio Workstations) can synchronize to time code although most will only read or generate MIDI time code. Therefore a card or external device is needed to (a) read MIDI and (b) convert SMPTE to MIDI and vice versa. |