12
AES and unlock switches
The ‘aes’ and ‘unlock’ switches can be set to ‘‘mute’ or ‘thru’. The behavior of the
CC1 in these modes is described in Chapters ‘Master mode’ and ‘Slave mode’.
Key Lock mode
If your CC1 is used in one setting most of the time you can use “Key Lock” mode to
prevent clocking errors by accidental pressing of control buttons on the CC1’s front
panel. In this mode the CC1 does not respond to the push of any button. “Key Lock”
mode is engaged by holding the “44.1/48/Slave” button during power up. It will
then lock the mode that was set before the last power down. To leave “Key Lock”
mode, hold the “44.1/48/Slave” button during power up again.
4. Setting up the Studio
In a digital studio all equipment will need to be synchronised. If all there is are two
boxes, one sending and one transmitting, all that is needed is a digital signal and
the recipient will lock to that. When multiple sources are feeding into one recipi-
ent (e.g. a digital desk connected to several digital recorders and converters), all
sources will need to be synchronous. This is what a house sync (aka master clock) is
for. Several formats are in use. The AES promotes a standard called AES11 that uses
an AES3 link, but most equipment tends to use a word sync signal on a BNC connec-
tor. The AES11 standard is to be amended to include this practice. We think this is a
good move, since the purity of a clock recovered from an AES3 link is rather suscep-
tible to issues like cable length and bandwidth limitations. The AES3 output on the
CC1 is provided to cater for the few equipment that needs AES11 over AES3. When
the output is not used for this purpose, it doubles as a jitter removal function for
any AES3 signal (provided it is synchronous with the CC1).
Most studios that have introduced a house sync have noticed a change in the overall
sound quality of their equipment. Usually for the better, sometimes for the worse.
At issue is jitter (akin to wow and flutter, but then applied to the sampling clock).
Chapter 6 “Jitter explained” will go into more details. The important point to remem-
ber is that jitter affects audio quality only at points in the chain where an actual
time-based conversion is taking place, typically AD and DA converters but also
increasingly asynchronous sampling rate converters.
Summary of Contents for CC1
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