Audio Feedback Frequency Detection Using Test Notch Decay
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Solution Overview
Problem
Existing feedback suppression systems in audio amplification systems often mistakenly identify musical tones as feedback, leading to unnecessary gain reduction and degradation of sound quality, and fail to accurately distinguish between feedback frequencies and harmonically related frequencies or distortion products.
Innovation Solution
A system that uses a three-layered Goertzel algorithm to analyze the growth characteristics of dominant spectral components over time, deploying a test notch filter to verify decay and distinguish feedback frequencies from musical tones by monitoring the signal's behavior after filter placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If overall gain is reduced to stop feedback growth, then feedback instability is eliminated, but the effectiveness of the amplification system is negated because the overall signal gain is reduced
Solution Approach 1:
The patent extracts only the problematic feedback frequencies from the overall signal spectrum and applies gain reduction selectively at those specific frequencies using notch filters, while leaving the rest of the frequency spectrum unaffected. This allows feedback suppression without reducing overall system gain.
Solution Approach 2:
The patent applies different gain characteristics to different frequency regions: strong attenuation at identified feedback frequencies and full gain preservation at all other frequencies. This localized approach eliminates feedback instability while maintaining overall signal amplification effectiveness.
2Reliability
If a feedback suppressor reduces gain at identified frequencies, then feedback is suppressed, but sustained musical tones with persistent frequencies are mistakenly turned down
Solution Approach 1:
The patent performs preliminary analysis of the signal to detect the growth characteristics of frequencies over time before applying suppression. By monitoring whether frequencies are growing (feedback) or stable (musical tones) before taking action, the system avoids mistaking sustained musical tones for feedback.
Solution Approach 2:
The patent uses dynamic monitoring of frequency magnitude changes over time to distinguish between feedback (growing magnitude) and sustained musical tones (stable magnitude). This dynamic approach allows accurate differentiation and prevents false suppression of musical content.
3Measurement precision
If harmonic content analysis is used to distinguish musical tones from feedback, then some discrimination is achieved, but systems with electronic instruments that do not produce traditional harmonics fail to be accurately identified
Solution Approach 1:
The patent changes the detection parameter from harmonic content analysis to growth rate analysis. Instead of checking for harmonic relationships that may not exist with electronic instruments, the system monitors the temporal evolution of frequency magnitudes, which is a universal characteristic applicable to all sound sources including electronic instruments.
Data Source
AI summary
A system and method for analyzing a signal to identify one or more candidate frequencies that may have a potential feedback problem. An electronic circuit for identifying feedback in an audio signal, formed in accordance with embodiments of the invention, may comprise a feedback control block operable to: 1) determine a magnitude of a first dominant spectral component in a wide-band span of frequencies of a signal, 2) determine a magnitude of a second dominant spectral component in a mid-band span of frequencies of the signal, and 3) determine a magnitude of a third dominant spectral component in a narrow-band span of frequencies of the signal. The feedback control block may then further analyze the magnitude and frequency of the first, second, and third dominant spectral components to determine the presence of feedback characteristics in the signal.