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The Feedback Ferret is an automatic feedback eliminator. Once it has been configured, it automatically detects and controls feedback.
The NWare Feedback Ferret device works in the same way as the hardware version, but uses the DSP resources of the NION instead of dedicated hardware.
Upon startup, the Ferret's 16 notch filters are initialized to pass the audio unaffected. As the Ferret analyzes the audio and detects a potential feedback condition, it assigns a notch filter. Filter 16 is the first filter assigned with an attenuation of 3 dB centered at the trouble frequency. If more attenuation is required, the filter depth will be progressively increased until the condition is resolved or maximum attenuation is reached. If the feedback is momentary, the filter will be slowly released in .1 dB steps until it either recurs or the filter response is returned to flat and is available for redeployment at the next emergency situation. If the filter depth is repeatedly increased at the same frequency, the filter will be locked at this frequency and from this point on will not be slowly released until there is a recompile of Filter Reset. The filter recovery feature ensures that the system uses filters only when needed and thus preserving maximum system fidelity.
Feedback control devices are typically used on the audio paths from the mixer to the Power Amps. This was mostly a system cost consideration and the Ferret works great here. In addition, the software flexibility of the Ferret within MediaMatrix allows the Ferret to be placed effectively in many new places. Dedicating a Ferret to a single troublesome lavaliere mic is an excellent insurance policy while minimizing the effect on the overall system sound. In addition, multiple mics can be summed and processed by a single Ferret. For those really cost sensitive applications, the control bussing of the Ferret filters introduces the concept of controlling multiple filter banks with a single Ferret.
The controls for the Ferret are minimal, consisting of 2 mode selections, a filter configuration select and "Panic" filter configuration. The Ferret provides all necessary configuration and control of the associated filter banks. No operator control is available for the filters.
Panic filters are a special class of filters deployed exclusively by the Peavey Feedback Ferret to address the situation of sudden, uncontrolled full-blast feedback. These filters are dispatched when large amounts of energy are concentrated in a single octave. To deal with this, the Ferret has a 2-step approach. Initially, the ferret detects this potentially dangerous condition and the need to take action. There may not be enough information to accurately place a narrow band notch filter, but something has to be done. The panic filter was designed specifically for this situation. The panic filter is deployed with a bandwidth of 1 octave at the approximate center of the problem. The filter is set aggressively, but to preserve sound fidelity, it is limited to a maximum depth of 6 dB. After the crisis is over, the filter is slowly released at .1 dB increments. If the problem recurs as the filter is released, the feedback will build back slowly and the standard, more accurate filter will be set to "kill" the feedback. The result is immediate response followed up with more accurate long-term control if needed.
Panic filters are brought in to attack the sudden, unexpected and really loud problems. To do this well, the system designer needs to help the Ferret with the definition of "loud". This is where the Panic Threshold comes in. For a typical MediaMatrix system, this control should be set just below Nominal operating level (0 dB). If, however; your design requires more of less headroom, the Panic Filter Threshold will need to be adjusted to compensate for your special situation. Setting this threshold too low may cause unnecessary filters to be set during normal program material. This control has no effect until Panic Filters are enabled.
Once filters have been allocated and locked by the Ferret, recompiling the view or pressing the "Filter Reset" button are the only 2 ways to clear them. During system setup and ring-out, the engineer may adjust the Eq of the system and then use the reset button as a way to tell the Ferret to start over. Before doing this, the engineer should make sure that the system gain is well below feedback, otherwise, serious system damage is possible when the filters that were restraining the Feedback Demon are released. After system ring-out, this control should NEVER be pressed. It's just too dangerous and the possible consequences are too grave (blown speakers and hearing) to allow an operator access to this control. For this reason, we have included an addition "are you sure" level to help prevent inadvertent operation. This control should never appear on the top level of a system view.
Slowly bring up the Microphone input gain control. As the system gain approaches feedback, tones or ringing will be heard and quickly killed by the Ferret. As a tone is heard, temporarily stop increasing the gain and allow the Ferret to complete the adjustment of the filters to accurately address the problem mode before going on to the next. Operation of the Ferret can of course be heard, and can also be seen by examining the filter display. During this part of setup, you should practically expect to increase the gain before feedback by 6 to 10 dB. As filters are set, the engineer should monitor the gain and the number of filters used. Setup should be considered finished when either: maximum input gain has been achieved without Feedback, or the Ferret has locked 6 filters, or system gain before feedback has been increased by 10 dB. Filters set during preshow are meant to control dominant room modes. For this reason, if more than 6 filters are needed to obtain the necessary sound level, then you should carefully review your system design looking for system design problems.
As mentioned earlier, a recompile will initialize the Feedback control filters to flat. Well then the question is "How do I keep my dominant mode settings that I just used preshow mode to configure?" I'm glad you asked. This brings up one of the most powerful reasons for combining MediaMatrix and the Ferret. The Ferret can be used to determine the correct parametric Eq settings and through the flexibility of MediaMatrix these settings can be transferred to MediaMatrix's native fixed Parametric Equalizers. Now all of the filters of the Ferret are available to control transient modes that occur as the sound terrain changes. Additionally, if dynamic control is not desired, the Ferret can be used as a diagnostic tool during setup and then to save DSP cycles, it can be removed from the final view, just leaving the Parametric Equalizers.
Caution: Never feed the filter control output from the Ferret to an audio output. This signal is NOT audio and may damage sensitive components if routed to an audio output.
Note: The Ferret is not intended as an alternative to good system design. With a good system design it can be an effective insurance policy for those unexpected little problems that always crop up when you least expect them. With a poor sound system design, the Ferret will only "band-aid" the problem and you will probably still not be pleased with the overall system performance. The Ferret is just another tool to help you do a better job easier and quicker.