HD24/96 Technical Reference

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The answer is that time code is used to synchronize the transport position, and word clock to synchronize the sample clock rate/speed of multiple devices. Although word clock synchronization always controls the sample rate of the slave units in the same way, there are two basic ways digital audio devices handle time code synchronization.

Jam Sync

Jam Sync is the method used in the HDR24/96, as well as every digital tape machine and most digital audio workstations. There are two variations of Jam Sync: Jam Once, and Jam Continuous. In both methodologies, once lock is acquired the transport position of the device is completely governed by the playback speed (i.e. Sample Rate) of the device without further reference to external time code. If drift occurs between the time code source and the slave, nothing is done to correct the drift. In other words, once the transport is locked and the position is set it, external time code is essentially ignored (“set it and forget it”). Jam Sync assumes that the clocks of all concerned devices are synchronized to the to the same clock source.

In Jam Continuous operation, the slave monitors the incoming time code signal for unexpected events (dropouts, garbled frames, abrupt changes in position). If nothing unexpected happens, the slave transport continues to play, even if drift accumulates. If time code stops or jumps suddenly to a new position, the slave either drops lock and stops or re-locks to the new position. Temporary anomalies are always overridden. This is the normal mode of time code sync operation for the HDR24/96.

In Jam Once operation, once the slave is locked, external time code is completely ignored and the transport continues to run until stopped by the user. Jam Once operation is most useful when recording or playback disruptions due to faulty time code cannot be tolerated (for example during live remote recording). To put the HDR24/96 in Jam Once operation, disable TC Chase after lock is acquired.

Trigger Sync

Trigger Sync is a method used by some non-linear digital audio devices (digital audio sequencers, workstations and disk recorders) and all non-audio (non-DAS) MIDI sequencers. Trigger Sync by its nature is never used on linear digital audio devices (DATs, MDMs). In Trigger Sync operation, the start or playback of every event on the slave is triggered based on incoming time code time rather than the slave unit’s internal time.

In a non-linear digital audio device, the event being triggered is actually the playback of recorded audio. Unlike Jam Sync where the playback position of the master and slave are aligned only once at lock, in Trigger Sync operation the slave unit’s position is continually realigned to the position of the master, and audio region playback always starts in sync with the master. However, once region playback starts, playback continues uninterrupted, even if the slave unit’s position is readjusted due to drift with respect to the master.

Trigger Sync operation can compensate for not having sample clock synchronization in projects containing audio regions shorter than 30 to 40s. In projects containing longer regions, the possibility exists that regions on the same unit can get out of sync with each other when slaved to time code, but play back in perfect sync offline, leaving you and your equally-bewildered support technician scratching your heads.

In a MIDI sequencer, the event being triggered is the transmission of one or more MIDI commands. Because MIDI commands are merely small data packets, there is no