HD24/96 Technical Reference

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One can also distribute word clock to all the digital audio devices from an external source (such as the Aardsync II from Aardvark depicted above) that generates both a master video blackburst and a resolved word clock output.

For smaller home setups inexpensive video blackburst generators are available for under $300. If you setup will not allow external video or clock synchronization (such as a consumer VHS machine) you can synchronize the HDR24/96 directly to the composite video output of the device. Although this is not ideal - the video output from a typical consumer VHS machine is not very stable - it will work in a pinch.

Working with Time Code

One situation that arises often is the need to lock a digital audio system to a “wild” time code source that is not referenced to either word clock or video. In the picture below, the HDR24/96 is locked to LTC that has been recorded onto one track of an analog multitrack tape machine.

LTC Time Code

Analog 24-Track

Time Code Slave

Time Code Master

In this example, the tape machine and the HDR24/96 will not stay in sync with each other because the setup is in effect identical to the example given at the beginning of section 3. Even though there is no sample clock in the multitrack machine, the net effect of the tape machine servo control mechanism and the LTC generator that originally striped tape is that of a sample clock with a slightly different tolerance than the HDR24/96 sample clock. The problem of synchronizing to wild time code sources can be dealt with in several different ways.

Just like a sample clock can be resolved to video, the sample clock can also be resolved to time code through a simple mathematical relationship. For example, if your HDR24/96 is set to a 48 kHz Sample Rate and a 30 fps Time Code Frame Rate, the relationship is governed by the following formula:

[48,000 samples/sec] / [30 frames/second] = 1600 samples/frame

This relationship says that for every 1600 samples that tick on the sample clock, 1 frame ticks on the time code display. Some digital audio devices will resolve their sample clocks to time code; the HDR24/96 does not. To make this setup work, an external device like the Aardvark Timesync II is needed to generate a resolved word clock from LTC.