Audio DSP with AEC, 4-in/4-out analog, 4-in/4-out Dante and USB
-18-
Filter Mode:
Each feedback filter has three modes: dynamic, manual and fixed. When manual mode is set, the gain can also be
manually set. When Fixed mode is set, the filter always works and will not be occupied by new feedback points; it still works
when being rebooted. When all eight filters are used and new feedback is detected, the module will
take one of the “Dynamic”
filters and use this to inhibit new feedback.
Clear:
Click the button to instantly clear up all filters. It will clear up all feedback points found previously.
The feedback filter section can be used as a tool during the system commissioning to identify feedback points or as a preventive
measure during normal operations. If you want to get higher system transmission gain and feedback inhibition effect, it is
recommended that you debug by following the steps below:
(a)
Reduce the system gain, and use the button "Clear" to reset all filter parameters
(b)
Set up parameters for the feedback filter module. Also, decrease the panic threshold to reduce the feedback level.
(c)
Open all microphones, and slowly increase system gain until the feedback occurs. Stop increasing system gain when
the feedback occurs.
(d)
Wait for the feedback inhibition module to take effect; after the feedback disappears, continue to increase gain.
(e)
Repeat the operation until the system reaches the required gain or until all filters are fully distributed
(f)
Change the panic threshold to a maximum level just higher than the expected non-feedback signal.
At this time, if needed, you may set Fixed mode for each filter or save the dynamic status to deal with possible feedback during
the performance period. Additionally, you may copy the filter to the notching filter module (parametric equalizer).
3.3.7 AutoMixer
A normal mixer is simply summing the signals. For every doubling of open microphones, the total gain will double. This will
amplify noise and room noise leaking into unused microphones.
The gain sharing automixer solve this problem by maintaining a fixed total gain. Unused microphones will be attenuated while
the microphones in use will be open, sharing the available gain.
To use the Automix, the direct routing of the microphone input channel should be disabled, and the output of the Automix should
be routed to the selected destination in the matrix.
The automix function can be activated for each channel independently. Disabling the automix function for a channel will pass
the signal through like a normal mixer, and not influence the automix algorithm.
There are two groups of control parameters in the automix module: main control parameters and channel control parameters.
(1) Main control parameters
Gain:
controls the main output volume of the automixer
Slope:
The slope control influences the attenuation of unused channels. If the slope is higher, the level of
the unused channels will be reduced. It is suggested that the value be set at or around 2.0. A slope parameter
set at 1.0 will make the automixer function like a normal mixer. If set at 3.0, the action will result in larger
gain reduction, which may sound unnatural. The bigger the value, the more the channel is opened and the
more the total attenuation. The recommended value is around 2.0.
Response Time:
Shorter response time ensure fast opening of microphones in use. Longer response time
gives a smooth operation but may cut off the start of a word if set too long. In practice the best effect will be
when response time is between 100ms and 1000ms. The autogain algorithm will open microphones faster
than closing them. Therefore, the start of words will not be cut off even with the response time at 100ms. If
set to several seconds, there will be a longer hold time of the response time in the automixer. The previous
active channel will remain open for several seconds.
Mute:
master mute for the automixer
On/off:
button for activating or deactivating the automixer function.
