Parametric Stereo Concealment for FM Mono Dropout
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Solution Overview
Problem
FM stereo radio receivers face challenges in maintaining stereo audio quality due to poor reception conditions, which often result in intermittent mono reception, as the side channel is more susceptible to noise, leading to degraded audio quality when mixed with the mid channel.
Innovation Solution
A system that generates a low noise stereo signal using parametric stereo parameters, even when the side signal is of poor quality, by detecting mono dropout situations and employing error concealment methods, including a concealment detection stage and an upmix stage to process the audio signal based on previously estimated parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the side channel is muted when reception conditions become noisy, then the overall audio quality is improved by avoiding noisy stereo output, but the stereo capability is lost and the receiver falls back to mono
Solution Approach 1:
The system performs preliminary error concealment by generating artificial side channel signals from the mid channel before the noisy side channel would degrade audio quality. This preliminary action allows the system to maintain stereo capability even when reception conditions deteriorate, avoiding the need to mute the side channel entirely.
Solution Approach 2:
The system creates a copy of the mid channel signal to generate the side channel signal when the original side channel becomes too noisy. By copying and processing the mid channel through parametric stereo synthesis, the system reconstructs a clean side channel that maintains stereo imaging without introducing noise from the degraded reception.
2Adaptability or versatility
If the receiver accepts the noisy side signal and outputs real stereo signal, then the stereo capability is maintained, but the audio quality is degraded due to noise in the left and right channels
Solution Approach 1:
The system extracts the useful stereo information from the mid channel by analyzing its spectral and temporal characteristics. By taking out the essential audio content from the clean mid channel and using it to synthesize a replacement side channel, the system separates the useful signal from the noisy side channel input.
Solution Approach 2:
The system changes the parameters of the side channel signal by deriving it from the mid channel through parametric relationships rather than using the directly received noisy side channel. This parameter transformation allows the system to maintain stereo capability while improving audio quality by eliminating noise through mathematical reconstruction.
3Reliability
If parametric stereo parameters are used to generate low noise stereo signal, then the audio quality is improved under poor reception conditions, but the system complexity increases due to parameter estimation and error concealment mechanisms
Solution Approach 1:
The system performs preliminary estimation of parametric stereo parameters from the mid channel before noise degradation occurs. By preparing and storing these parameters in advance, the system can quickly switch to using them for side channel reconstruction without complex real-time processing during poor reception conditions.
Solution Approach 2:
The system uses the mid channel signal itself to generate the side channel signal through parametric relationships, rather than requiring separate processing of both channels. This self-service approach reduces system complexity by making the side channel generation dependent only on the clean mid channel and pre-estimated parameters.
Data Source
AI summary
The present invention relates to audio signal processing. In particular, it relates to a method and system for reliably concealing intermittent mono reception of FM stereo radio receivers. The system comprises a parametric stereo parameter estimation stage configured to determine a first parametric stereo parameter based on a first frame of the received two-channel audio signal. The system further comprises a concealment detection stage configured to determine an energy of a side signal within the first signal frame; determine a number of following successive signal frames during which the energy of the side signal drops from a value above the high threshold to a value below a low threshold; determine that the two-channel audio signal following the first signal frame is a forced mono signal if the number of successive signal frames is below a frame threshold; and determine the parametric stereo parameter based on the first parametric stereo parameter.