Feedback Suppressor (FBS) Dialog Overview

See topic, FBS Operation, for more information.

The FBS dialog box provides the following global buttons:

• Clear All - clears all dynamic filter settings.

• Lock - locks the Dynamic Filters to current settings, preventing the dynamic filters from being updated or over-written. This is a temporary mode, useful while testing the system, or during the time when dynamic filters are being converted to fixed filters to keep dynamic filters clear until the user decides to further ring out the system.  When the FBS display window is closed, the lock mode is automatically disengaged.

• Bypass - sets all Dynamic Filters to bypass mode. Does not affect Fixed Filters.

• Set Defaults - resets all values with user default settings.

The FBS dialog window contains the following three tabs:

• Settings

• Dynamic Filters

• Fixed Filters

Global settings and view options are controlled from the Settings tab, while dynamic to fixed filter allocations and all filter parameters are handled from the Dynamic Filters and Fixed Filters tabs, respectively.

Settings Tab

• For Composite View Only - content of the graph view is set by one of three radio buttons.

o Only Dynamic FBS Filters

o Only Fixed FBS Filters

o Dynamic & Fixed FBS Filters (default)

• Q - adjusts the notch filter Q that is used by dynamic filters. The default setting can be modified in Tools | Options. Settings range is from 5 to 65. Larger values provide less change to the audio frequency response while lower values may provide greater feedback suppression but with more possible impact to the tonal response of the source audio. Suggested values for specific applications are as follows:

o Q=7 for Voice with considerable feedback potential.

o Q=30 for Voice with less feedback potential (default).

o Q=65 for Music with minimal feedback potential.

• Attack Time - sets the time at which dynamic filters are generated after feedback detection. A larger attack time (e.g., an attack time of 200 ms or more) reduces the chance that music or audio content will undesirably trigger the dynamic filters to respond.  A shorter attack time (e.g., an attack time of 2 ms or less) reduces the time a feedback occurs before it is detected and suppressed.

• Hold Time - expressed in hours:minutes:seconds up to 9 hours, hold time sets the time that a dynamic filter setting persists before the filter is cleared. After the hold time, the filter is cleared and a new setting can be detected. Note that when a filter is cleared, feedback may occur again at the same frequency causing a new dynamic filter to be engaged. When hold time is disabled, dynamic filters will persist indefinitely until they are cleared manually, or until the device is power cycled. Hold time reverts to 00:00:00 when disabled.

Dynamic Filters Tab

This tab contains the fifteen dynamic filters, with a scroll bar to display filters hidden due to window size. Frequency and cut values are grayed until a filter is generated. Dynamic Filters are in auto-detect mode when the FBS block is active, i.e., when Bypass is disengaged. Once filter values are established to the satisfaction of the system designer, the Lock button may be engaged to avoid any further changes to filter settings (optional). The lock mode of operation is temporary, and is intended to be used during setup of the FBS.  When the FBS dialog window is closed the lock mode is automatically disengaged.

The Move to Fixed button will send the designated filter setting to the first available filter in the Fixed Filter tab, and automatically clear the filter. The Clear button will negate all established parameters for the corresponding Dynamic Filter. A cleared filter reverts to auto-detect mode (if the Lock button is engaged, this will only occur after the Lock state is defeated).

Fixed Filters Tab

The Fixed Filters are inactive, and the filter type is set to "Unused" by default. No filter parameters are displayed when the filter type is set to Unused. When a filter is moved to the Fixed Filter tab from the Dynamic Filter tab, the filter becomes active and will display "Notch" as the filter type, plus display all parameters, i.e., Frequency, Cut, and Q. Once a filter is active as a Fixed Filter, settings can be modified or adjusted as needed, though this is not generally necessary.