HD24/96 Technical Reference

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provide the timing accuracy necessary to insure that digital audio signals are received within the acceptable time window.

The picture below illustrates the relationship between the sample clocks of two digital audio devices locked to a common word clock signal (left) and a common video signal (right).

In the case of word clock synchronization, the rising edge of each device’s sample clock is always phase-aligned such that digital audio signals are always transmitted and received within the acceptable time window. In the case of video synchronization, the phase relationship of the sample clocks drifts randomly such that, at times, digital audio signals may fall outside the acceptable time window. Additionally the phase relationships often vary over time due to the nature of the video resolving circuitry.

To solve this problem, whenever video is used to synchronize analog audio/video and digital audio equipment together, all digital audio equipment should be synchronized to word clock from a single master clock source that is resolved to the video signal.

Since the HDR24/96 can resolve its sample clock to video and generate a resolved word clock output, it offers a straightforward solution to this problem. The illustration below shows the proper way to make digital audio devices synchronize to picture under all circumstances.

VTR

Video / Word Clock

Generator

Blackburst

Blackburst

Video Slave

Video-Resolved

Word Clock

Video

Slave /

Clock Slave

Clock

Master