There are two universal problems in the live events market where IMAG (image magnification) is used to supplement the live action onstage.
The first is the seemingly inevitable lip-sync delay caused by system latencies between the lenses of the cameras and the final output on the projection screens. This is especially true of smaller systems depending on a switcher/scalar/synchronizer device to connect together all the video components.
The second is the long-term reliability, and short-term dependency, of the converters used between various computers’ outputs and the SDI/HD-SDI video world.
In Figure 1, the signal flow between the camera and the projection lens is delayed by a number of processing steps. This is clearly no fault of the equipment itself, but is an unfortunate side effect—of depending on the capabilities of some devices to make up for deficiencies in others. The main causes—and their potential effects— are shown in red text.
Most consumer cameras are almost certainly “free-running,” meaning that they generate a video signal using their own internal sync generation. Over time, such a camera will be almost a frame “early” compared to what is being processed by the video switcher.
The switcher adds just enough delay to this early signal so that it appears to be in time with the switcher’s own matrix, but there are additional processes downstream which can sometimes add up to six frames of latency.
The system needs some upgrades and re-engineering so that the dependencies on “self-synchronizing” or “scaling” features can
be eliminated, which would remove most of the causes of system latency (see Figure 2).
Upgrading the cameras to accept a genlock (reference) signal is the first job. By installing a Grass Valley ADVC G4, the cameras and the production switcher will be operating on the same reference signal, which eliminates the need to frame-synchronize the cameras. As to the output, installing a projector that does not have to “scale” the image in any way (including digital keystone/size/position functions), and depends mostly on optical (in-the-lens) correction, reduces yet another contributing factor to the latency issue.
Deploying the ADVC G1 as a “synchronizing converter” provides a rock-solid interface between the computer and the SDI/HD-SDI/3G production world. It properly buffers and synchronizes the computer’s DVI/HDMI output to feed the production switcher, resulting in a system which minimizes latency to the smallest possible amount.
Figure 1 – System Design Contributing to Projection Feed “Lip-Sync” Errors.
Figure 2 – Professional System Design - Minimizing Projection “Lip-Sync” Errors
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