HHB comm CDR-882 - Manual (Page 39)

Advanced Features & Operation
 CDR-882 User Manual Version 1.0 www.hhb.co.uk
Advanced Features & Operation
Internal & External Clocks
Word clock in the CDR-882 can be obtained from several
sources. An internal crystal oscillator is provided, which is the
preferred source for use with analogue input signals. When
digital input signals are used, the word clock may be extracted
from the AES/EBU or S/PDIF bitstreams themselves. A further
option is to use a separate external clock signal.
In many professional digital audio systems, a separate external
master clock is used to synchronise all digital audio equipment
in the system; the CDR-882 is provided with an external word
clock input for use in such a situation.
Clock selection in the CDR-882 is normally automatic, the
source being selected to suit the audio input being used. The
following rules apply to the automatic selection system:
If an analogue input (Balanced or Unbal) is selected, the
CDR-882’s own internal clock will be used
If a digital input (AES/EBU, S/PDIF Coax or Optical) is
selected, the signal itself will be used as the clock source,
as long as it is within the acceptable frequency range,
namely 44.1kHz +/-100ppm
If a digital input is outside this range the internal clock will
be used, and the input signal sample rate converted to the
internal clock frequency
The choice of the internal clock for analogue inputs or the
embedded word clock for digital inputs will give perfectly
satisfactory results in most recording situations. However, it is
possible to override the automatic selection described above and
use a different word clock source.
The Clock submenu is used to select a different word clock
source from that chosen automatically. See page 31 for full
details.
Overriding the automatic selection allows the user to:
Use either an external master studio clock or a digital
audio signal (AES/EBU or S/PDIF) as word clock source
when using analogue inputs. This may be desirable for all
but the simplest digital audio systems as it ensures that
the clocks of all interconnected equipment are in exact
synchronisation
The external clock may be derived from a dedicated
generator, in which case it will be applied to the rear
BNC connector and Wordclock selected as the source
in the menu. Alternatively, “digital silence” can be used
in the form of an AES/EBU or S/PDIF signal without
audio content; in this case, Digital Input is selected as
the source and the appropriate input connector used.
Whichever inputs are being used, an external word clock
input must meet the CDR-882’s frequency requirements of
44.1kHz ± 100ppm
Use an external master studio clock as the word clock
source when using the CDR-882’s digital inputs. Again,
this will be connected at the Word Clock input and
Wordclock selected as the source. In this case, the word
clock connected to the CDR-882 must also be connected
as an external clock to the source of digital audio
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Use the CDR-882’s internal clock source with digital
inputs. This situation will occur when the CDR-882 is the
clock master in a system. A typical scenario would be
where the digital output of a semi-professional PC sound
card is feeding S/PDIF to the corresponding inputs of
the CDR-882. In such a case, it is likely that the CDR-
882’s internal clock’s stability will be better than that of
the sound card’s. The CDR-882’s digital outputs can be
connected to the inputs of the sound card, to be used
as its clock. The CDR-882 thus acts as the master clock
source
Clock Source Display
The front panel LCD always indicates the currently-selected
word clock source, whether the selection has been made
automatically or manually.
Internal - the internal master clock
DIG - an AES/EBU or S/PDIF digital audio signal at the
appropriate rear connector
WCLK - a word clock signal applied at the rear BNC
connector
If external word clock is selected, and the applied clock signal
has a frequency outside the range 44.1kHz +/-100ppm,
synchronisation is not possible and the WCLK indication will
flash. Similarly, if Digital Input is selected, and the applied signal
has a clock frequency outside this same range, synchronisation
will not be possible and DIG will flash. In these cases, the
problem will need to be resolved before a recording can be
made, either by correcting the clock frequency of the external
source or by selecting Internal or Auto instead.
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