7th Sense Delta User Manual - Page 6

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Marking Time

Audio Time

LTC audio tracks carry embedded SMPTE timecode, which enables multiple servers to synchronise their

playheads to an external LTC timecode. This code is essentially time reference meta data. If the server is

not genlocked to the LTC source, this can cause drift between audio and video, showing up easily in lip-

synced media, although not obvious with ambient or soundtrack audio.

Matching Movie and Audio Tracks

For 'pure playback' on DeltaServer systems, playback rates must be coordinated properly from top to

bottom. From production to media render to Delta timeline settings, to desktop/EDID settings or SDI

format settings and house sync, to signal transmission path, display – everything should be designed

and purposed to work in the same refresh (or multiple of the same refresh). However, DeltaServer

copes with a degree of tolerance even when not everything is perfect.

By placing audio and movie resources on a timeline, we lock them together in time. In limited scenarios,

a movie frame rate can be compensated for by giving it more or less real time in display, using the

Playspeed adjustment. If an audio track is frame-adjusted it may discernibly change pitch and go out of

tune in relation to other tracks or sound sources, depending on the amount of adjustment, though

DeltaServer can compensate for this with its own pitch correction. The best solution is to design the

media playback to a consistent framerate.

We can sync timelines between servers, and even better, genlocked to an external timing source. But

what happens when media do not all start at a frame reference of zero? Or when loudspeakers at a large

outdoor projection are a significant distance from viewers? Any individual resource can be repositioned

on a timeline to provide positive or negative time adjustment, and additionally all audio on a server can

be offset in DeltaServer Configuration Defaults by a given number of frames (plus or minus).

Delta Time

Delta time is based on movie time: i.e. the smallest unit of time is the frame, according to frame rate.

In smaller systems, and for shorter show lengths, Delta servers can simply be placed in the same Timing

Group, so that their timelines are internally synced. A master Delta server will broadcast its timeline

position as a series of binary timing packet to slave servers in the group, so that the playheads of every

timeline in every server are synchronised. However, without a common genlock source, servers may

drift between each other over a longer continuous play time. We may want all devices to refer to a

central clock and a central timecode instead.

Communications Integrity

Delta master-slave communication is carried out over the network. For analogue timing sync

connections, long runs of unshielded or unbalanced cable can cause signal loss and noise in timing

signals, so RCA/phono, BNC or mini-XLR connectors and coax or balanced cable should be used.

Synchroni s i ng Del ta Medi a Sys tems