FM Receiver Processor Noise Suppression via Frequency Domain Gain

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Solution Overview

Problem

FM signal reception quality deteriorates in noisy conditions, particularly due to the difference signal being more susceptible to noise, which affects the stereo audio signals more than the mono signal, leading to degraded audio quality.

Innovation Solution

A processing unit is employed that converts the FM difference signal and noise signal into the frequency domain, applies noise suppression using a gain function limited to maximal and minimal values, and combines this with adaptive gain factors to reduce noise in the difference signal before recombining it with the sum signal, thereby enhancing the audio signal quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If noise suppression is applied to the difference signal, then the signal-to-noise ratio is improved, but audible artifacts are introduced

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidaudible artifacts

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent applies frequency-dependent gain factors to the difference signal in the frequency domain, adjusting the noise suppression level at different frequencies. This allows selective noise reduction while preserving signal quality and minimizing audible artifacts by adapting the suppression strength to the spectral characteristics of the signal and noise.

Inventive Principle:

Principle #35Parameter changes

2Object-generated harmful factors

If the gain function is limited to maximal and minimal values, then audible artifacts are reduced, but the noise suppression effectiveness is compromised

Engineering Contradiction:

Improveaudible artifactsVSAvoidnoise suppression effectiveness

Core Design Contradiction:

Object-generated harmful factorsVSMeasurement precision

Solution Approach 1:

The patent applies different gain factors to different frequency components of the difference signal. By making the noise suppression locally adaptive in the frequency domain rather than uniform, it achieves effective noise reduction in noisy frequency regions while maintaining signal integrity in clean regions, thus reducing audible artifacts without compromising overall suppression effectiveness.

Inventive Principle:

Principle #3Local quality

3Measurement precision

If adaptive gain factors are applied to the difference signal, then the signal quality is enhanced, but the processing complexity increases

Engineering Contradiction:

Improvesignal qualityVSAvoidprocessing complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces complex time-domain noise processing with frequency-domain processing using FFT-based transformation. This allows adaptive gain factors to be applied efficiently in the frequency domain, achieving enhanced signal quality through systematic spectral manipulation while maintaining computational feasibility through established signal processing algorithms.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS9172479B2Processor for an FM signal receiver and processing method

Publication Date: 2015.10.27 NXP BV

AI summary

A processing unit for processing a multi-channel audio signal has a delay element (40) for delaying an FM sum signal (sum) and a converter arrangement (T) for converting an FM difference signal (diff) and a noise signal (diffnoise) to the frequency domain. Frequency-based noise suppression is used to derive a de-noised frequency-domain difference signal using a gain function which is limited to a maximal and a minimal value. This is then converted to the time domain, and the first and second audio signals are calculated from a delayed sum signal (sum2) and the de-noised time domain difference signal (diff2).