MDCT Complex Prediction Stereo Decoding Without QMF Delay
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Solution Overview
Problem
Existing stereo audio coding methods, particularly at higher bitrates, suffer from high computational complexity due to the use of QMF-based approaches, leading to inefficiencies and increased delay.
Innovation Solution
Implementing a decoder system that utilizes critically sampled MDCT transform for complex prediction stereo coding, eliminating the need for additional QMF transforms, and allowing adaptive decoding between conventional and complex prediction methods, with optional TNS filter placement and computation optimizations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If QMF-based approaches are used for stereo audio coding, then stereo coding capability is achieved, but computational complexity increases and delay increases
Solution Approach 1:
The patent extracts and removes the QMF transform stage from the decoding process, retaining only the essential MDCT-based complex prediction functionality. This eliminates the computationally intensive QMF analysis and synthesis filter banks while preserving stereo coding capability through direct MDCT domain processing of downmix and residual channels.
Solution Approach 2:
The patent substitutes the mechanical QMF filter bank system with a more efficient MDCT-based computational approach. By using complex prediction coefficients applied directly in the MDCT frequency domain, the system replaces the heavy mechanical filtering operations with lighter complex arithmetic operations, significantly reducing computational complexity.
2Reliability
If QMF-based approaches are used for stereo audio coding, then stereo coding capability is achieved, but delay increases
Solution Approach 1:
By removing the QMF transform stage entirely, the patent eliminates the inherent delay introduced by QMF analysis and synthesis filter banks. The direct MDCT-based complex prediction approach processes frames without the additional transformation steps, thereby reducing overall system delay while maintaining stereo coding functionality.
3Productivity
If complex prediction stereo coding is implemented, then coding efficiency improves, but device complexity increases
Solution Approach 1:
The patent designs the decoder to handle multiple coding modes (conventional and complex prediction) within a unified MDCT-based framework. The same MDCT processing infrastructure serves both simple conventional decoding and more advanced complex prediction decoding, eliminating the need for separate processing paths and reducing overall device complexity despite enhanced functionality.
Data Source
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AI summary
The invention provides methods and devices for stereo encoding and decoding using complex prediction in the frequency domain. In one embodiment, a decoding method, for obtaining an output stereo signal from an input stereo signal encoded by complex prediction coding and comprising first frequency-domain representations of two input channels, comprises the upmixing steps of: (i) computing a second frequency-domain representation of a first input channel; and (ii) computing an output channel on the basis of the first and second frequency-domain representations of the first input channel, the first frequency-domain representation of the second input channel and a complex prediction coefficient. The method comprises performing frequency-domain modifications selectively before or after upmixing.