MACKIE HDR 24/96 - Manual (Page 99)

HD24/96 Technical Reference 99
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.
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.
T i m e C o d e S l a v e
L T C T i m e C o d e
A n a l o g 2 4 - T r a c k
T i m e C o d e M a s t e r