Axis Communications 230 MPEG-2 - Manual (Page 54)

Audio Settings AXIS 230 54
Appendix E - Audio Settings
The maximum audio level depends on the configuration used.
• Selecting external microphone and high sensitivity input, sets the 0dB level (the maximum
level) to 25mVpp.
• Selecting external microphone and low sensitivity input, sets the 0dB level (the maximum
level) to 270mVpp.
• Selecting external line input sets the 0dB level (maximum level) to 3.0 Vpp.
The Audio LED remains unlit as long as the audio level is below -20dB, as compared to the
maximum audio level, which is defined as 0dB.
The LED turns green when the audio level is between -20dB and 0dB. This is the optimum
audio level. The LED turns red if the audio level rises above the clip level (the maximum
level), that is, above 0dB.
Generally speaking, normal speech at a distance of 1 meter will, in high sensitivity mode,
produce sound levels high enough to light the LED green. When the microphone is set up
in a noisy environment, it may be necessary to set the sensitivity to "low," otherwise the
clip level will be reached and the sound will become distorted. For very high sound
pressure levels, use an external microphone with a controlled output level.
The audio “event" (as used to trigger events) always correlates to if the green LED is lit. By
using different input settings, the audio event trigger level can thus be given different
values.
The master volume does not affect the maximum levels into the A/D-converter in the
camera, nor does it affect the audio input LED or the trigger level for the audio event. The
master volume is only a gain factor that changes the already sampled and digitized signal.
For this reason it is important that the signal is handled within the correct dynamic range,
by changing the sensitivity settings rather than the master volume - otherwise the signal
may become distorted due to input overload.
The Master volume can be used to match other PC-produced "wave sounds", since there is
no separate volume control for the decoded audio in the PC sound card interface. This
means that system sounds in the client computer are affected by the same volume control
as the incoming sound from the Axis 230.
Normally, the Audio LED monitors the input level and will show red if the audio input
signal is too strong, which will also be apparent as the sound becomes distorted. However,
increasing the Master Gain may cause distortion at other levels, which will not be
indicated by the Audio LED. For this reason, increasing the Master Gain when the Audio
LED shows almost constant green is not recommended.