Audio Signal Processing Circuit for Noise Suppression Without Phase Shift
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Solution Overview
Problem
Existing audio signal processing circuits in radio receivers suffer from deteriorated sound quality due to abrupt phase changes when noise suppression is activated, as they rely solely on low-pass filtering, which introduces delays and affects the overall audio signal phase.
Innovation Solution
An audio signal processing circuit incorporating a noise detecting unit, low-pass and high-pass filters with predetermined phase characteristics, and coefficient control units that adjust amplification coefficients to maintain in-phase audio signals and suppress noise effectively, ensuring consistent sound quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low-pass filter is used to suppress noise in the audio signal, then the noise suppression effect is improved, but the sound quality deteriorates due to abrupt phase changes
Solution Approach 1:
The audio signal is divided into multiple frequency bands using band-pass filters with different center frequencies. Each frequency band is processed independently with its own low-pass filter and noise suppression coefficients, allowing phase characteristics to be maintained while suppressing noise. This segmentation approach resolves the contradiction by enabling selective noise suppression in each band without affecting the overall phase integrity of the audio signal.
Solution Approach 2:
The invention dynamically changes the suppression coefficients (alpha and beta) based on the detected noise level. When noise is detected, the coefficients are adjusted to increase low-pass filtering effect; when no noise is present, the coefficients are adjusted to minimize filtering effect. This parameter change approach allows the system to adapt between noise suppression and sound quality preservation, resolving the contradiction between these two opposing requirements.
2Object-affected harmful factors
If the switch is switched to the low-pass filter when noise is detected, then the noise effect is suppressed, but the audio signal phase changes abruptly
Solution Approach 1:
The invention uses dynamic coefficient adjustment instead of abrupt switching. The suppression coefficients are continuously adjusted based on noise detection results, allowing the filtering characteristics to transition smoothly between different states. This dynamic approach prevents abrupt phase changes while maintaining effective noise suppression, resolving the contradiction between noise suppression and phase stability.
3Object-affected harmful factors
If noise suppression is applied using low-pass filtering, then the multipath noise is suppressed, but the volume of the audio signal is reduced
Solution Approach 1:
The invention applies different suppression coefficients to different frequency bands based on their specific characteristics. Each band-pass filter output is processed with tailored low-pass filtering and coefficient adjustment, allowing noise suppression to be applied locally where needed while preserving the overall volume and quality of the audio signal. This local quality approach resolves the contradiction by enabling selective volume preservation alongside noise suppression.
Data Source
AI summary
An audio-signal-processing circuit includes: a noise-detecting unit to detect presence or absence of noise in an audio signal generated based on an output from a tuner configured to receive a broadcast signal; a low-pass filter, having predetermined phase characteristics, to pass the audio signal having a band of frequencies lower than a predetermined frequency; a high-pass filter, having the predetermined phase characteristics, to pass the audio signal having a band of frequencies higher than the predetermined frequency; first- and second-output units to multiply the signals outputted from the low-pass and high-pass filters by first and second coefficients and output the multiplied signals, respectively; an adding unit to add the signals respectively outputted from the first and the second output units; and a coefficient control unit to, when the noise-detecting unit has detected the presence of noise, decrease the second coefficient below the first coefficient.