Timing Sources - 7th Sense Delta Media Server User Manual

Synchronising delta media systems

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Timing Sources

Sync Generators

DeltaServer syncs its frame playback to the server GPU clock (in 'Auto' or 'Hardware Timed' modes), and

each GPU can be synced in turn to a central house sync clock. Such sync pulse generators and word clocks

do not convey data, only a highly accurate bit-rate as a common timing (not time) reference. Sync pulse

generators are used for graphics display synchronisation, whereas word clocks are the standard for

synchronising audio devices. Some audio devices have their own internal word clock.

LTC sources

Linear timecode (LTC) provides much more. Whilst the LTC signal is digital in structure, the transmission

is traditionally analogue – typically as a .wav audio file with a bit-stream rate of around 1 kHz to 2.5 kHz,

in order to be safely within audio range. This is encoded with the required framerate, sample rate, bit

depth and duration, to the SMPTE 12M specification. The data block for each frame has 80 bits. These

include 26 bits to carry the SMPTE time, and 32 that can carry optional user data (for example, relating to

the media for which it is intended). The final 16 bits of the block comprise a fixed bit-pattern 'sync word'

that an LTC reader uses to define the frame boundary, play direction, and bit-rate of the sync tone.

Delta Master-Slave Timing

Synchronisation between media players, media resources, display, effects and projection equipment

can be fairly complex, and real clock time is not used. However, agreement on the duration of a second,

and relative time position do matter. Timestamp markers running through media resources provide all

the reference needed for the Delta timeline, which in turn can broadcast the timeline playhead

position. Another Delta server receives that position, and its playhead takes the same position on its

timeline (i.e. 'play this same frame no. now'). A Delta slave server playhead will then always be in the

same position as the master it is listening to, and will be frame-accurate to ±1 frame when no genlock is

present, or frame-accurate with genlock. The downside is that if the master server fails, timeline

reference is lost across all servers and the show will stop. Here a Delta master and three slaves are

timeline synchronised, taking their clock reference from the master server GPU, and all GPUs and

displays are house-synced:

Synchroni s i ng Del ta Medi a Sys tems

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