Chapter 8: Audio Module, Rev 1.1
8.4.6.2 Microphone Self-Testing
Every 12 hours VDR Record application performs microphone self testing to determine if the VDR
is recording audio from the microphones. An explanation of the self-test procedure is as follows:
The buzzer 1 bank of the audio module is activated and all buzzers connected to this
bank are turned on.
Then buzzer 2 bank of the audio module is activated and all buzzers connected to bank 2
are turned on.
Note!. Each buzzer bank is energized for the period specified in the vdrparams.ini file – the
ChirpLength field (ChirpLength is specified in milliseconds: default is 30).
The RMS for the entire data record (1 second) for each input channel is computed;
If the RMS value of this one second test period is greater than 0.707 * detection
threshold, the test is aborted. If this happens the background noise level is assumed to
be too high to reliably pick out the buzzer chirp;
The log window will show the test on that channel was aborted;
If the test is not aborted, an RMS value is computed for each sub-interval;
Note! Each sub-interval is half the ChirpLength duration.
If 1 or more of the calculated sub-intervals exceeds the detection threshold, the chirp is
declared detected and the microphone operational;
Once the test source on each channel has been activated, the detection results are
reviewed;
Any mic that has failed the test will be retried;
The VDR-100G3 will wait for the period specified in the INI file (the MikeRetryInterval
field) before retrying the test;
The test will be retried a maximum number of times (as specified in the INI file – the
MaxMikeRetrys field.);
If any 1 microphone fails all self-test attempts, a Micxx Error alarm (E.g. Mic07 error) will
be generated; and
The alarm will not clear until all microphones have been successfully tested on that
channel.
NOTE: If the DetectionThreshold value in the <vdrparams.ini> file is set too high, the chirp
from the test source will not be detected and the test will fail resulting in a mic error message.
If the DetectionThreshold is set too low the microphone test will be aborted. This will not
create an error message but the microphone testing will be incomplete and will continue to
retry every hour until the test is successful.
VDR-100G3/G3S Installation Manual 06/10/2008
8-31
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