Feedback Suppressor (FBS) Overview

FBS is used when there is a danger of feedback in live situations. The FBS detects feedback on a live microphone channel and uses a set of up to 5 fixed filters and 15 dynamic filters to counteract the frequency peaks at the detected feedback frequencies.

See the FBS Operation section for more information.

Inserting an FBS Processor

  1. Open the context menu using one of the following methods:

  2. Double-click the FBS (feedback suppressor) block in the DSP Configurator workspace.

  3. Right-click the FBS block to open the context menu.

  4. Click the FBS block to select it (or use the arrow keys to navigate to the FBS block) and press the <Enter> key on your keyboard.

  1. From the drop-down menu, select Feedback Suppressor. Alternatively, if you right-clicked the block, select Insert Feedback Suppressor. The FBS block color changes to a shade of brown.

To adjust the FBS settings, double-click the FBS block. The Feedback Suppressor dialog box opens. See the "Feedback Suppressor Dialog Components" subsection below for information about the settings that are available in the dialog. See the FBS Operation section for information about setting up the FBS.

Feedback Suppressor Dialog Components

The Feedback Suppressor dialog contains the following global buttons:

  • Clear All - Clears all dynamic filter settings

  • Lock - This option locks the dynamic filters to the current settings, preventing the filters from being updated or overwritten. This is a temporary mode that is useful when you test the system or when you convert dynamic filters to fixed filters in order to keep dynamic filters clear until you decide to further ring out the system.

  • Bypass FBS - Sets all dynamic filters to Bypass mode. This does not affect fixed filters.

  • Set Defaults - Resets all values to the user default settings

The dialog contains the following three tabs of controls:

  • Settings - This tab allows you to control the global settings and view options.

  • Dynamic Filters - This tab allows you to manage the dynamic to fixed filter allocations.

  • Fixed Filters - This tab allows you to manage the filter parameters.

Settings tab

The following settings are available on the Settings tab of the Feedback Suppressor dialog.

  • For Composite View Show - Sets the content of the graph view. You can click one of the following radio buttons to display the respective content in the graph.

  • Only Dynamic FBS Filters

  • Only Fixed FBS Filters

  • Fixed & Dynamic FBS Filters

  • Mode - You can click the Up and Down Arrows or manually enter a value in the Q field to adjust the notch filter Q that is used by dynamic filters. You can modify the default setting in Tools > Options (see the Options section).

    The setting range is 5 to 65. Larger values provide less change to the audio frequency response while lower value can provide greater feedback suppression but with more possible impact to the tonal response of the source audio. The suggested values for specific applications are as follows:

  • Q = 7 for voice with considerable feedback potential

  • Q = 30 for voice with less feedback potential (default)

  • 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 (an attack time of 200 ms or more) reduces the change that music or audio content will undesirably trigger the dynamic filters to respond.

    A short attack time (an attack time of 2 ms or less) reduces the time a feedback occurs before it is detected and suppressed.

  • Hold Time - Select the Enable check box to enable the hold time, which is expressed in <hours>:<minutes>:<seconds> up to nine hours. You can adjust the hold time by clicking the Up and Down Arrows or manually entering values for the hours, minutes, and seconds. 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 can occur again at the same frequency, causing a new dynamic filter to be engaged.

    When the hold time is disabled (the Enable check box is cleared), dynamic filters persist indefinitely until they are cleared manually or until you power cycle the device. Hold time reverts to 00:00:00 when disabled.

Dynamic Filters tab

The Dynamic Filters tab contains fifteen dynamic filters. Use the scroll bar to display filters hidden due to the window size. Frequency and cut values are disabled until you generate a filter. Dynamic filters are in auto-detect mode when the FBS block is active. This is when bypass is disengaged. After filter values are established to the satisfaction of the system designer, you can engage the Lock button to avoid any further changes to the filter settings (optional). Locking the dynamic filters is temporary and is intended to be used during the FBS setup. When you close the Feedback Suppressor dialog box, Lock mode is automatically disengaged.

Click the Move to Fixed button to send the designated filter setting to the first available filter on the Fixed Filter tab, which automatically clears the filter. Clicking the Clear button negates 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 exiting the Lock state).

  

Fixed Filters tab

Fixed filters are inactive and are displayed on the Fixed Filters tab. 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 Filters tab, the filter becomes active and displays Notch as the filter type (see image below). The filter also displays all of the parameters ( frequency, cut, and Q). After a filter is active as a fixed filter, you can modify the settings as needed, though this is generally not necessary.