AXYS
®
Octadrive DSP-DN User Manual rev 2.0
201703/ODSPDN_2.0
16
The Input Mode setting in WinControl (at
Input >
Common parameters
) allow selection of auto-
switching mode. A brief description of each mode follows;
see the WinControl Help files for full details.
Normal
Auto-switching is disabled. All inputs are active, and
summed. Use this mode if only one input is in use.
level-Controlled Priority Switching
When enabled, the inputs will switch when the signal
level at the detection point drops below -60 dBFS (default
value), but this threshold may be set to any level between
-80 dBFS and -20 dBFS. The detection point is either ‘At
input’ or ‘After processing’. In the latter case filtering may
be applied, for example to reduce the level of an input
pilot tone. When using analogue inputs, the relationship
between dBFS and dBV’s measured at the device’s inputs
should be taken into consideration; WinControl’s Help files
give full details.
It is also possible to set a Hold Time, so that unwanted
switching does not occur between natural gaps in the
programme.
Pilot Tone-Controlled Priority Switching
It is common practice in critical audio systems to
permanently route a low level, high-frequency tone
through the system. The presence of this pilot tone can
then be detected by various items of equipment to verify
the continued operation of the audio paths. Set Input
Mode to Pilot tone-controlled priority switching to enable
this mode.
The Octadrive DSP-DN’s pilot tone detector on the analogue
inputs operates in the frequency range of approximately 20
kHz to 28 kHz. The detector is most sensitive in the center
of this frequency range, the detection threshold is not
software configurable. On the digital (Dante
™
) inputs the
frequency range is 19.2 kHz to 23.5 kHz and the threshold
may be set between -10 dBFS and -60 dBFS.
The Octadrive’s action on non-detection of a pilot tone
can be configured via WinControl. A fault condition can be
“flagged”, and/or the input can be set auto-switch to that
with the next priority.
A notch filter should be inserted to suppress
the pilot tone if its frequency is less than half
the internal processor’s sample frequency (F
s
/2, typically
24 kHz). If the pilot tone is not sufficiently suppressed,
signal detection (and other functions such as frost
protection and Autogain) will not function properly.
Further, this may result in excessive dissipation
downstream, in the power amplifiers and/or connected
loudspeakers, or interference with the internally-
generated pilot tone. Pilot tone frequencies above F
s
/2 are
sufficiently suppressed by the anti-aliasing filter of the
ADC. Any pilot tone frequency received via the digital inputs
is < Fs/2 by default.
Take notice of the following when configuring the
parameters for the input pilot tone detection:
It is advised to use a few seconds of Grace time
in order to avoid spurious input pilot tone
monitoring errors.
Use a fixed frequency if the frequency of the
externally applied pilot tone is known and fixed.
See WinControl help file for details.
Failure Relay
The two-pole changeover failure relay may be wired to a
‘common fault’ or other external fault monitoring system
so that any fault condition detected by the Octadrive
DSP-DN is immediately reported. The conditions which
cause activation of the failure relay may be defined in
WinControl, and may include any or all of: DSP, microphone,
PTT switch, pilot tone detection, mains supply, DC back-up
supply, internal supplies, Dante
™
board clock faults etc.
See the WinControl Help files for full details.
If it is required to interface the Octadrive DSP-DN
to impedance-sensing fault-monitoring equipment such
as the AXYS
®
Cerberus, failure relay Contacts 2 should
be used. See “fig.8: Failure relay” on page 12 for
connection details.