A3Measuring Audio/Video Delays

An OmniTek system can be used to measure either absolute audio and video delays through external equipment, or can measure the relative delay between the audio and video paths. The OmniTek modules and options required are different between the two modes. The Advanced Option is required. This appendix describes what OmniTek products are required for each mode, and how to configure the OmniTek system in each mode.

Both measurement modes rely on the use of a special full-motion video test sequence which contains precise embedded audio tones. This sequence is available for all standard-definition and high-definition video formats, and may be played out either from an Gen signal generator (equipped with the Motion option) or simply from a videotape machine or video file server.

The following sections describe the OmniTek delay test sequence, and show how it may be used to perform audio and video delay analysis on external equipment.

A/V Delay Test Sequence

OmniTek have generated a special full-motion video sequence, 192 frames in duration. This is available in all video formats, both standard- and high-definition. The test sequence contains many elements which are useful for testing and analysing the performance of a video system, however for the purposes of the audio/video delay measurement there are two characteristics which are of special importance:

On the first frame of the sequence only, an embedded audio tone of 8kHz is generated on channel 1 at a level of –18dB(FS).

In the top left-hand corner of each frame, a binary frame count is displayed as a sequence of yellow squares.

In the View analysis software, the binary frame count can be extracted from the input video image, and the embedded audio tone is also detected. The relative timing of the audio tone to the first video frame in the sequence indicates the delay between audio and video components.

This is a binary count of the 192-frame	When the clock hand reaches the top (frame 0),
sequence, 0x00 ~ 0xBF (hex)	an audio pulse is generated for 1 frame duration

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