Ashly nX1504 Operating Manual page 28

Operating Manual - nX, nXe, and nXp 150W/75W Power Amplifiers
Ambient Noise Compensation (output channels only)
Ambient noise compensation (ANC) is an automatic output level control
that uses a microphone to monitor background noise in a specific zone, then adjusts
the output level to that zone accordingly in order to maximize intelligibility. One
amplifier input channel must be dedicated to the sensing microphone and cannot be
used for other inputs.
nX amplifiers do not have mic preamps, so an external mic preamp is
required. The mic preamp output is then connected into any input on the nX ampli-
fier other than the program audio channel in which the ANC function is engaged
on. The ambient noise signal is then processed similar to a slow-responding SPL
meter which is then used as the control signal for the automatic level control of the
program audio/paging signal.
The ambient noise sensing microphone doesn't need to be a high-quality
microphone because it is only used to pick-up the overall noise level in the room
and is not used for the direct program audio or paging. The placement location of
this noise-sensing microphone is very important for the ambient noise compensation
function to work well. A unidirectional microphone pointed toward the noise sources
and away from any speakers works best.
ANC Meters and Controls
Input Level Meter - The input level of the program audio before ANC gain/attenuation is applied.
Attenuation Meter - The gain/attenuation automatically applied to the program audio by the ANC function.
Max Gain - Sets the maximum gain that you allow the ANC to apply to the program audio. A typical starting value is
10 dB.
Min/Base Gain - Sets the minimum gain that you allow the ANC to apply to the program audio. A typical starting
value is -20 dB. This also sets the starting gain value once the noise exceeds the threshold. The minimum gain is +1dB.
Gain Change Rate - The rate at which the ANC will change the gain as measured in seconds per dB. A typical starting
value is 2 seconds/dB.
Link Group - The channel group assignment for linking multiple channels parameters. Use this feature to link stereo
program audio channels to track each other in gain changes in response to ambient noise change.
Average Noise Meter - The level of the ambient noise signal at the point where it enters the matrix mixer and the ANC
function.
Mixer Input Channel - The input channel selected for the ambient noise sensing microphone. The microphone signal
is taken at the point where it enters the matrix mixer, after any input signal path processing.
Noise Threshold - The noise-sensing signal level above which you desire the ANC to start to increase the program
audio gain above the minimum gain. A typical starting value is -30 dBFS. Keep in mind that any changes to the gain of the
noise-sensing microphone will affect the setting of the noise threshold control.
Program/Ambient Gain Ratio - The ratio of dB increase in program level for every 1 dB increase in ambient noise
level. A typical starting value is 1.0 which means that for every 1 dB increase in ambient noise, the ANC will automatically
increase the gain of the program audio by 1 dB.
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