Q & A: Video Processor
A reader sends in a question regarding sychronizing the feed from a video processor with its audio feed.
Q: I have a video processor that I use to feed a projector. As expected, the image from the video source is delayed by the processing, so I've acquired an audio delay to sync things back up. Has anyone done this before, and measured the actual video delay with a video processor? I've eye-balled it for now, but would like to get a more exact number.
— Mark Wyse, director of theatrical arts, Blackhawk Church, Madison, WI
A: All scalers will delay the video signal with respect to the audio because of the complex internal signal processing. For example, Kramer's ProScale digital scaler/switchers, like the VP-723ds, have a maximum delay of approximately three frames or 50 ms (3*1/60 = 50 ms), depending on the input signal type. (Delay for a composite video signal will be worse than for a progressive-scan component video signal). It's important to note that delay is a cumulative effect. Sources and display devices may also add varying amounts of delay. To solve the delay problem, Kramer manufactures the VA-256 audio delay processor. By using a series of dip-switches, the VA-256 can correct up to 2.7 seconds of delay in 10 ms increments.
— Chris Kopin, vice president of product development, Kramer Electronics, Hampton, NJ