MACKIE HDR24/96 - Manual (Page 204)

HDR 24/96
the box. Using the above examples again, if the HDR24/96 is set to 60 Hz Video Field Rate, a 48
kHz Sample Rate, and a 30 fps Time Code Frame Rate, locking the HDR24/96 to a 60 Hz video
signal produces a 48 kHz sample clock and 30 fps time code. Simple.
Safe Synchronization
Everything you have just learned above can be summarized into a few handy rules and maxims.
Recite these rules 20 times each day until they become permanently etched into the neural pathways
of your brain.
1. No two clocks ever run at exactly the same speed. Period. This phenomenon of nature
cannot be corrected by living in denial and pretending everything will be OK if you
don’t synchronize the clocks.
2. Devices can be correctly synchronized only by matching the speed of their primary
timing/drive mechanisms and aligning the position of their transports with respect to
time.
3. All synchronization signals used in a setup, including time code, video, and word clock,
MUST be resolved to each other. Failure to do so will result in drift between two or
more devices in the setup.
4. All digital audio devices that share digital audio signals must be locked together using
word clock, superclock, or AES Null. Failure to do so may result in pops and clicks if
digital audio paths are connected between various devices. The HDR24/96 has NO self-
clocking I/O interfaces. Word clock must be used instead.
5. Addendum to previous rule: Some digital audio devices have self-clocking interfaces. In
other words, the sample clock of the unit (for locking digital audio devices) can be
derived from the signals that carry the digital audio. This is true of many devices that are
capable of receiving AES, S/PDIF, or ADAT Optical signals. In the case of self-clocking
interfaces no "additional" clock is needed.
6. Time code and video signals are not sample clock signals; word clock, superclock, and
AES Null are. Some devices, like the HDR24/96 can derive their Sample Clock from
video. Others can derive their Sample Clock from time code.
7. When left to choose between using MTC or LTC, use LTC.
8. If a device does not support all six of the standard Time Code Frame Rates, make sure
you understand how the nomenclature is used in relationship to these six rates. The use
of time code terms on that device may differ from other devices in your studio.
9. When doing pull-ups or pull-downs, make sure you understand exactly how the
equipment you are using works to avoid the pitfalls of inconsistent nomenclature and
methodology.
10. When reading LTC from or feeding LTC to analog tape it is best to use a time code
reshaper/regenerator in the signal path. Never use EQ, compression, or noise reduction
on LTC.
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