Feedback Suppressor (FBS) Operation

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. It is possible to achieve an additional 3 dB to 9 dB of gain on mic channels where feedback would have otherwise prevented these levels.

See the FBS Overview section for more information.

Dynamic Filters

Dynamic filters auto-detect feedback frequencies when FBS is switched on (unbypassed). Dynamic filters are notch filters with a user-defined Q setting and a variable cut, providing gain reduction up to 30 dB at a narrow frequency band. Prior to engaging the FBS dynamic filters, you can modify the default Q setting in Tools > Options. The Q setting is further defined on the Settings tab of the Feedback Suppressor dialog (see the
FBS Overview section).

NOTE:  Changing the Q setting after dynamic filters have been generated will clear all dynamic filters.

Fixed Filters

Fixed filters are notch filters with an adjustable center frequency and Q setting, a possible cut of up to 30 dB, and a recommended cut of less than or equal to 24 dB. The fixed filters are typically set by converting the dynamic filters to fixed. Fixed filters are typically not set manually, though further adjustments are possible on the Fixed Filters tab of the Feedback Suppressor dialog (see the FBS Overview section).

Using FBS

There are two approaches to using the FBS:

  • Load and Go

  • Ring Out

You can clear dynamic filters by clicking the Clear button for each filter. You can then use the filters for feedback that may occur during a live event (such as with moving microphones), or for additional feedback suppression by further pushing the mic gain. For the latter, mic gain should be reduced slightly when feedback can no longer be suppressed.

To begin setting up the FBS:

  1. Set the mic/line input and mic mix-point (see the Optimizing Audio Levels section).

  2. Insert an FBS processor into the desired mic/line input channel. See the FBS Overview section for the procedure, information about the Q setting, and details about other FBS parameter and display options.

Using the Load and Go method

With the Load and Go approach, the FBS is loaded into the processor block and engaged so that the dynamic filters are active and will detect and counteract feedback if needed. In this case, only the dynamic filters come into play. No operator setup is required, though some settings are recommended. This approach works fine for a system that does not operate near the point of feedback but needs protection (such as from a moving microphone that may come too close to a speaker and potentially cause feedback).

To use the Load and Go method:

  1. Double-click the FBS block. The Feedback Suppressor dialog box opens.

  2. Click Bypass FBS to disengage Bypass (it is engaged by default). The FBS processor is now engaged.

  3. Optionally, engage and set the hold time for the dynamic filters (see the FBS Overview section).

Using the Ring Out method

In the Ring Out approach during system setup, feedback is forced by raising mic gain to the point of feedback while testing the microphone (simulating live operation). The FBS detects the feedback and the dynamic filters are automatically set to reduce level at the feedback frequencies.

After being set, the dynamic filters can be converted to fixed filters by clicking the Move to Fixed button for each filter. You can choose any of the dynamic filters for this purpose. Filters with a larger amount of cut, or those filters generated first, can be considered the most likely to give feedback. These are good candidates for conversion to fixed filters. A dynamic filter automatically clears when it is converted to a fixed filter.

To use the Ring Out method:

  1. Double-click the FBS block. The Feedback Suppressor dialog box opens.

  2. Click Bypass FBS to disengage Bypass (it is engaged by default). The FBS processor is now engaged.

  3. Raise the mic/line input gain until feedback starts to occur. Allow the FBS to detect one or more frequencies until feedback is suppressed.

  4. Repeat step 2, if desired. This process may continue until all dynamic filters have detected feedback frequencies. After this occurs, attenuate the mic level by 2 dB to 3 dB.

  5. Click Lock to engage the Lock setting. This is optional. Doing so locks the current set of dynamic filters and prevents dynamic filters from being detected during the "Move to Fixed" procedure in the next step (step 6). Lock is a temporary setting and disengages when the Feedback Suppressor dialog closes.

  6. For each dynamic filter, click the Move to Fixed button in order to dynamic filters to fixed filters. You can move up to five dynamic filters. It is your discretion as to which filters are moved. Logical choices, for example, would be the last five dynamic filters or the five filters with the largest cut value.

  7. Choose one of the following actions to complete the FBS setup.

  8. Click the Lock button to disengage the Lock setting (if you engaged it in step 5) and close the Feedback Suppressor dialog. This leaves five dynamic filters open if spontaneous feedback occurs.

  9. Click the Bypass button to engage Bypass. Some feedback may occur, so attenuate the mic level as needed. This procedure retains the detected filters (if needed) but leaves only the fixed filters in play.