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6.
AUDIO ALARM CALIBRATION PROCEDURE
This section contains detailed descriptions outlining how to set the various audio warning/error detection
parameters.
Some of the audio alarm detection algorithms are dependent on the state of other audio alarm detectors.
For instance, the mono detection algorithm will not use periods of silence as determined by the silence
detection. For this reason, the following sequence should be used to calibrate the audio alarms. The
items in italics refer to menu items in the AVC. Please refer to section 7.7 for a complete description of
the fault definition menu items.
6.1.
CALIBRATE AUDIO SILENCE DETECTION
1. Supply the card with the plant's noisiest audio feed without any audio program material present. This
will be a baseline noise level to calibrate the silence detector.
2. Turn off all sources of errors in a Fault Condition and assign Audio Silence as the only error. Also, be
sure to set the Fault Duration to a small number of frames in order to see when the error condition
disappears.
3. Set the Silence Duration to 0.5 sec to view the results of adjusting the Silence Level parameter without
getting confused by the detection time.
4. Adjust the audio Silence Level until the Fault Condition begins to go active. This will be the noise floor
level. Raise the Silence Level a few dB to make the detector insensitive to this noise level.
5. Set the Silence Duration to a time appropriate to the application. This should be set to a value longer
than the worst case acceptable quiet period.
6.2.
CALIBRATE AUDIO PHASE REVERSAL DETECTION
1. Supply the card with a stereo signal that has the phases reversed. Ensure that the material is typical of
normal content for this channel.
2. Turn off all sources of errors in a Fault Condition and assign Phase Reversal as the only error. Also,
make sure that the Fault Duration is set to a small number of frames in order to see when the error
condition disappears.
3. Set the Phase Reversal Duration to 0.5 sec to view the results of adjusting the Phase Reversal Level
without getting confused by the detection time.
4. Adjust the Phase Reversal Level so that the Fault Condition detects the phase reversal.
5. Set the Phase Reversal Duration to a time period appropriate to the application.
Periods of silence (below the Silence Level) will extend this duration. In other
words, periods without audio content are not included in the phase reversal
detection.
Stereo material with long periods of dissimilar left/right content (for example,
music with plenty of panning) may cause the phase reversal detector to fire. It
is best to set the Phase Reversal Duration to a value larger than what would be
expected.
7735AVC-LB Video Composite Encoder and Audio DAC with SoftSwitch
Revision 1.6
7700 MultiFrame Manual
7735AVC-LB - 13
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