Stereo Audio Decoding With Variable Prediction Direction
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Solution Overview
Problem
Existing multi-channel audio processing techniques face challenges in achieving high coding gain while maintaining audio quality and reducing computational complexity, particularly in situations where mid/side coding does not yield optimal results due to phase shifts or amplitude differences between channels.
Innovation Solution
A method and apparatus for stereo audio decoding that uses a prediction of a second combination signal from a first combination signal, derived from the original signals using a mid/side combination rule, with a frequency-domain encoding approach and a critically sampled transform like MDCT, and adaptive prediction direction selection based on energy levels to enhance coding gain and reduce computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If mid/side coding is applied to stereo audio signals, then coding gain is improved when channels are similar, but bit rate increases when channels have phase shifts or amplitude differences
Solution Approach 1:
The patent applies dynamic switching between different coding modes (mid/side coding, independent coding, and hybrid coding) based on the correlation between left and right channels. The coding mode is adaptively selected according to the signal characteristics in each frequency band, allowing the system to optimize coding gain while controlling bit rate by choosing the most appropriate coding strategy for each specific situation.
Solution Approach 2:
The patent changes the coding parameters dynamically by adjusting the prediction coefficient and switching between different coding modes based on the correlation measure between channels. When correlation is high, mid/side coding with prediction is used to maximize coding gain; when correlation is low, independent coding is used to maintain audio quality while controlling bit rate.
2Productivity
If parametric stereo coding is used to reduce bit rate, then productivity is improved, but audio quality deteriorates due to information loss
Solution Approach 1:
The patent segments the audio signal into different frequency bands and applies different coding strategies to each band based on local correlation characteristics. This allows the system to use efficient parametric coding where applicable while maintaining full waveform coding in bands where it preserves audio quality, thus balancing bit rate efficiency and audio fidelity.
Solution Approach 2:
The patent creates a composite coding approach by combining mid/side coding, independent coding, and predictive coding in a hybrid framework. This composite strategy leverages the advantages of each individual method: the coding gain of mid/side coding, the quality preservation of independent coding, and the efficiency of predictive coding, achieving both bit rate reduction and audio quality maintenance.
3Manufacturing precision
If frequency-selective mid/side coding is applied to maintain coding gain, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality optimization by using frequency-selective mid/side coding where the coding mode is chosen independently for each frequency band based on local correlation characteristics. This allows the system to apply complex processing only where necessary (bands with high correlation) while using simpler coding in other bands, thus optimizing coding gain without uniformly increasing complexity across the entire system.
Data Source
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AI summary
An audio or video encoder and an audio or video decoder are based on a combination of two audio or video channels (201, 202) to obtain a first combination signal (204) as a mid signal and a residual signal (205) which can be derived using a predicted side signal derived from the mid signal. The first combination signal and the prediction residual signal are encoded (209) and written (212) into a data stream (213) together with the prediction information (206) derived by an optimizer (207) based on an optimization target (208) and a prediction direction indicator indicating a prediction direction associated with the residual signal. A decoder uses the prediction residual signal, the first combination signal, the prediction direction indicator and the prediction information to derive a decoded first channel signal and a decoded second channel signal. In an encoder example or in a decoder example, a real-to-imaginary transform can be applied for estimating the imaginary part of the spectrum of the first combination signal. For calculating the prediction signal used in the derivation of the prediction residual signal, the real-valued first combination signal is multiplied by a real portion of the complex prediction information and the estimated imaginary part of the first combination signal is multiplied by an imaginary portion of the complex prediction information.