Feedback suppressor

Afeedback suppressoris anaudio signal processingdevice which is used in the signal path in a livesound reinforcement systemto prevent or suppressaudio feedback.

Digital feedback reductionis the application of digital techniques tosound reinforcementin order to reduceaudio feedbackand increaseheadroom.

Operation

Feedback suppressors use three main methods to control feedback,

• frequency shifting,
• adaptive filteringand
• automaticnotch filtering

Frequency shifting is the oldest feedback suppression technique dating back to the 1960s. This technique works by introducing a varying shift in frequency to the system response. This is typically implemented using afrequency mixer.Only modest improvement of gain before feedback is achievedand the technique creates noticeablepitchdistortion in music program.

Theadaptive filter approachworks by modeling the transfer function of the sound reinforcement system and subtracts the reinforced sound from the inputs to the system in the same way that anecho cancellerremoves echoes from acommunications system.

Parametric equalizationand notch filters are commonly used bysound engineersto manually control feedback. A feedback suppressor using the automatic notch technique listens for the onset of feedback and automatically inserts a notch filter into the signal path at the frequency of the detected feedback. Feedback suppressors use several techniques for detecting feedback from non-invasiveharmonic analysisof a potential feedback signal to more invasive adaptive filtering and speculative placement of notch filters. The automatic notch technique is the most popular method and has the advantage that the sound is not colored until the system is at risk of feedback.