MACKIE HDR24/96 - Manual (Page 191)

HDR 24/96
hours, minutes, and seconds hands perfectly lined up, we know that they would always read exactly
the same time, forever and ever. Just like the watches, to synchronize two or more digital audio
recorders to synchronize to each other, two things have to happen: hours, minutes, and seconds hands perfectly lined up, we know that they would always read exactly
the same time, forever and ever. Just like the watches, to synchronize two or more digital audio
recorders to synchronize to each other, two things have to happen:
1. The Sample Clocks of all the devices have to run at exactly
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1. The Sample Clocks of all the devices have to run at exactly the same speed (i.e. Sample
Rate), and --
2. The transports need to start at exactly the same position at exactly the same time.
The first requirement is satisfied by distributing a common Sample Clock signal to every device. One
device is configured as the Master and generates the Sample Clock, and all the others are configured
as Slaves that lock their Sample Clocks to the Master. Word Clock is a standard Sample Clock signal
format that many devices support, including the HDR24/96. Word Clock runs at a frequency exactly
equal to the Sample Rate, and is transmitted using 75-ohm coaxial cable.
Several other clock signal formats exist, including AES Null clock and oversampled word clock (also
called superclock), which runs at 128, 256, and 384 times the Sample Rate. Although the rest of our
discussion about clocks will be limited to Word Clock, (the HDR24/94 supports Word Clock only),
the principles apply to all of these clock formats.
The second requirement is satisfied by distributing a common time code signal to every device. The
time code signal carries coded information about what time it is at any particular instant. One device
is configured as the Master and generates time code, and all the others are configured as Slaves that
lock their transport positions to time code from the Master.
There are several common time code signal formats, including LTC (longitudinal time code,
sometimes called SMPTE LTC, or just SMPTE), MTC (MIDI time code), and VITC (vertical interval
time code). The HDR24/96 supports both LTC and MTC, but not VITC. LTC is an audio-frequency
signal and may be carried over standard audio cabling, routed through your console, and recorded just
like any analog audio signal. MTC, unlike LTC, is not an audio-frequency signal and cannot be
directly recorded; it’s transmitted exclusively over MIDI cables through MIDI devices. VITC is a
time code signal that is embedded into a composite video signal, and must be encoded and decoded
by special video signal processing devices.
The correct way to synchronize two HDR24/96 units together is shown below:
Master HDR24/96 Slave HDR24/96
Time Code
Word Clock
The master machine on the left generates both word clock and time code, and the slave machine on
the right locks to word clock and time code from the master. As long as the Sample Clocks of both
units are locked to each other, it doesn’t matter which unit generates time code. The example below
shows a different way of setting up two HDR24/96 units that is also correct. In this example the
machine on the left generates word clock and locks to time code, and the machine on the right locks
to word clock and generates time code.
Technical Reference 191