User Manual

ALF-DSP 88-U
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If two channels have the same signal level, then the channel with higher priority will receive more au to gain. If there
is one-unit difference in priority level between them, then the channel with the higher priority level will get an ex tra
gain of 2dB (supposing the slope of the two channels are set at 2.0). For example, if channel 1 and 2’s priorities are
respectively set at 6 and 3, and the input level of those two channels are the same, then Channel 1 will receive 66dB
gain more than Channel 2. During operation, please note that the slope setting of the main control parameters
influence gain difference brought by the priority weight of channels. If the slope is set at 3.0, then one priority level
difference will result in a gain difference of 4dB.
Note: In some cases, be very careful when using wide priority differences between channels, such as a priority of 0
and 10. If channels with ultra-high priority recognize signals like background music from a loudspeaker, then it is
possible for them to mask channels with lower priority. The effect will get worse if the slope is higher too. If the
issue occurs during installation and commissioning, users may consider installing a noise gate or expander between
the auto mixers of the highest priority channels. Also, con side r setting a threshold at a value that it won’t be
opened by the noise gate or expander.
3.4.12 Acoustic Echo Cancelation
Acoustic Echo Cancelation (AEC for short) is used in audio / video conferencing to facilitate full duplex
communication. The AEC module increases the remote speaker’s phonetic intelligibility by cancelling out or
removing unwanted acoustic echo generated in the local room’s audio system (between the microphones and
speakers).
Echo cancellation module for remote calls can be used to carry out local amplification of remote voice signals and
attenuate the interference caused by acoustic echo. Its basic operation principle is simulating echo channel,
estimating possible echo generated by remote signals and then minus the estimated signal from input signal of
microphones, and thus there will be no echo generated in input voice signal to achieve the goal of cancelling echo.
There is only one echo cancellation module in the DSP Controller. Two local inputs and remote output mixers are
preset to realize multichannel signal participating in echo cancellation as shown in figure.
One parameter can be adjusted, name ly the Non-linear filter (NLP). There are three preset filters to choose from:
Conservative, Moderate and Aggressive can be selected to determine the acoustic echo suppression level.
Note: The settings of the Acoustic Echo Cancellation module can be used cooperatively with the matrix module to
determine signal routes.