FM Pulse Noise Suppression Using Composite Signal Validation
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Solution Overview
Problem
In digital FM radio receivers, weak electric field conditions lead to dominant background noise, making it difficult to detect and remove pulse noise, resulting in sound distortion due to misoperation, as conventional methods struggle to distinguish between pulse noise and high-frequency components of music or speech.
Innovation Solution
A noise suppressing device that band-limits the composite signal to a frequency lower than a predetermined threshold, includes a pulse detecting unit to identify pulse noise, and a pulse judging unit to validate detection, allowing for accurate suppression of pulse noise without misoperation, using a comparator to synchronize the amplitude of the composite signal with the detection interval and compare it to a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional pulse noise canceller with AGC circuit and noise detection circuit is used, then misdetection due to background noise is suppressed, but pulse noise cannot be detected at weak electric field conditions where background noise becomes dominant
Solution Approach 1:
The invention segments the detection process into two independent pathways: one for detecting pulse noise characteristics (using high-pass filter and AGC) and another for detecting background noise characteristics (using band-pass filter and AGC). This segmentation allows the system to independently analyze pulse noise signals even when background noise is dominant, resolving the contradiction between detection accuracy and misdetection suppression.
Solution Approach 2:
The invention introduces background noise characteristics as an intermediary reference. By detecting background noise levels separately and comparing pulse noise detection results against this reference, the system can distinguish true pulse noise from background noise fluctuations, enabling accurate pulse noise detection even when background noise is dominant while preventing misdetection.
2Object-affected harmful factors
If the reception electric field deteriorates to weak electric field conditions, then background noise becomes dominant, but pulse noise detection becomes extremely difficult leading to misoperation and sound distortion
Solution Approach 1:
The invention dynamically adapts the detection threshold based on real-time background noise characteristics. By continuously monitoring background noise levels and adjusting the pulse noise detection threshold accordingly, the system maintains optimal detection sensitivity across varying electric field conditions, enabling pulse noise detection even when background noise becomes dominant at weak electric field conditions.
Solution Approach 2:
The invention changes the detection parameters (threshold levels, filter characteristics) based on the electric field strength and background noise conditions. By adjusting these parameters dynamically, the system overcomes the increased detection difficulty at weak electric field conditions while preventing misoperation caused by excessive sensitivity to background noise.
3Measurement precision
If a high-pass filter is used to detect pulse noise, then pulse noise can be extracted from the composite signal, but high-frequency components of music or speech are also detected causing misoperation
Solution Approach 1:
The invention segments the detection process into pulse noise detection pathway and background noise verification pathway. By separating these functions and requiring both pathways to confirm pulse noise presence, the system achieves accurate pulse noise extraction while filtering out false detections from high-frequency music or speech components.
Solution Approach 2:
The invention uses background noise characteristics as feedback to validate pulse noise detections. By continuously monitoring background noise levels and comparing detection results against this feedback, the system can distinguish true pulse noise from high-frequency components of music or speech, reducing false detections while maintaining accurate pulse noise extraction.
Data Source
AI summary
To provide a noise suppressing device which accurately suppresses weak electric field strength pulse noise.A band-limiting unit (5) band-limits a composite signal obtained by demodulating an FM baseband signal, to a frequency band equal to or lower than a predetermined frequency so as to output a monaural audio signal. A pulse detecting unit (62) which detects pulse noise in the audio signal outputted by the band-limiting unit (5). A pulse judging unit (63) judges that a detection result of the pulse detecting unit (62) is valid in the case where pulse noise is detected in the composite signal, at a position corresponding to the detected pulse noise. A pulse suppressing unit (64) suppresses the pulse noise detected in the audio signal, in the case where the pulse judging unit (63) judges that the detection result is valid. Specifically, the amplitude of the composite signal which is synchronized with the audio signal is compared with a threshold, and it is judged that the detection result is pulse noise in the case where the amplitude of the composite signal exceeds the threshold.