ALF-DSP88-U
-23-
The feedback suppressor module has the following adjustable parameters:
Panic Limiter Threshold:
According to this parameter, any level higher than the threshold is absolutely “feedback”. When a
signal level is higher than the feedback threshold, any of the following circumstances will occur; a) the output gain is
temporarily attenuated to control the speed of feedback; b) the output level is restricted to prevent out of control feedback;
c) the filter's sensitivity is increased for faster detection and feedback. Once the output level is lower than the threshold, the
gain will be recovered, and the sensitivity is restored to normal state. This value refers to the peak value of the digital range
signal. If the value is set as 0, this function is disabled.
Feedback Threshold:
According to this parameter, "any level lower than the threshold is absolutely not feedback". This may
prevent the module from detecting feedback in a soft music or due low noise level.
Filter Depth:
It refers to the maximum attenuation of a single filter. A shallow setting may prevent excessive frequency or
signal degradation caused by the notching filter to the original signal. A deep notching filter may cause worse feedback
control, especially in a large narrow resonance system.
Bandwidth:
1/10 and 1/5 Oct options can be chosen. A constant Q value is adopted. The filter will not become wider due to
the increase of depth. It is recommended to use the filter in the phonetic environment. In the case of frequent feedback, the
bandwidth is set at 1/5 Oct because it has wider bandwidth and greater influence.
Preset:
There are four built-in presets: "big music room", "small music room", "big voice room" and "small voice room".
These four presets apply to the default settings for most applications.
Notching Filter's Auto Mode:
When Auto mode is set for the notching filter and after eight filters are in use, when new
“feedback” is detected, the module will “check” the auto filters and use it to inhibit the new feedback. Each notching filter
has three modes: auto, manual and fixed modes. When Manual mode is set for the filter, 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. If you need to save these feedback parameters, please click to save the preset button.
Clear All:
Click the button to instantly clear all filters. It will clear up all feedback points detected previously. This operation is
generally done when recommissioning the feedback module.
Feedback suppression can be used as a tool during 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 suppression, it is
recommended that you debug the system by following the steps below:
(a) Reduce the system gain, and use the "Clear" button to reset all filter parameters
(b) Set up fine-tuned parameters for the feedback suppressor module. Also, decrease the panic threshold to reduce the
feedback level.
(c) Open all microphones, and slowly increase system gain until feedback occurs. Stop increasing system gain when
the feedback occurs.
(d) Wait for the feedback suppressor 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 normal operation. Additionally, you may copy the filter to a notching filter module (such as the equalizer). In this
way, you may add more feedback filter capacity.
If a speaker is included among the devices used, it is recommended to use a compressor / limiter module for additional
protection. You may set an appropriate limiter to make sure that the speaker will not get damaged even if all notching filters
are used up, or the feedback inhibitor cannot effectively control the feedback, such as in the case of excessive system gain.
Summary of Contents for ALF-DSP88-U
Page 13: ...ALF DSP88 U 13 2 5 Audio Flow...
Page 42: ...ALF DSP88 U 42...
