Complex Subband Filter Banks for Low-Complexity Audio Coding
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Solution Overview
Problem
Current audio encoding techniques, such as SAC, SBR, and PS, face challenges in achieving transparent audio quality due to high computational complexity and quality degradation, particularly when combining waveform and parametric encoding methods.
Innovation Solution
A decoder and encoder system that utilizes a synthesis filter bank for both parametric and waveform decoding/encoding, allowing for subband processing without converting back to the time domain, reducing complexity and enhancing correlation between encoding methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the time domain signal is transformed back to frequency domain using QMF synthesis for waveform coding enhancement, then audio quality is improved, but computational complexity and processing burden increase significantly
Solution Approach 1:
The patent merges the waveform coding enhancement path directly into the frequency domain by processing the complex sub-band domain signals from the QMF analysis bank without transforming back to time domain. This combines the parametric extension framework with waveform coding capabilities while avoiding redundant time-frequency transformations, thereby improving audio quality without significantly increasing computational complexity.
Solution Approach 2:
The patent performs waveform coding enhancement operations on the complex sub-band domain signals before the final QMF synthesis step. By preparing the enhanced frequency domain signals in advance and directly feeding them into the QMF synthesis bank, the system avoids the need for intermediate time domain transformations, reducing processing burden while achieving transparent audio quality.
2Adaptability or versatility
If different waveform coding systems are used for different parametric extension combinations, then system adaptability is improved, but device complexity and interoperation difficulty increase
Solution Approach 1:
The patent creates a universal frequency domain waveform coding enhancement mechanism that works with any parametric extension system (SBR, PS, SAC, etc.). By operating directly on the complex sub-band domain signals produced by the QMF analysis bank and feeding the enhanced signals back into the QMF synthesis bank, the system provides a unified interface that is compatible with multiple parametric extension standards, improving adaptability while maintaining decoder simplicity.
3Reliability
If complex sub-band domain signals are oversampled by factor of two, then aliasing distortion is reduced, but processing efficiency decreases
Solution Approach 1:
The patent processes the complex sub-band domain signals in a segmented manner, operating on each sub-band independently in the frequency domain. This allows efficient processing of the oversampled signals without requiring full time domain transformation, maintaining the aliasing distortion reduction benefits of oversampling while improving processing efficiency through targeted frequency domain operations.
Data Source
AI summary
An encoder (109) comprises a receiver (201) which receives a time domain audio signal. A filter bank (203) generates a first subband signal from the time domain audio signal where the first subband signal corresponds to a non-critically sampled complex subband domain representation of the time domain signal. A conversion processor (205) generates a second subband signal from the first subband signal by subband processing. The second subband signal corresponds to a critically sampled complex subband domain representation of the time domain audio signals. An encode processor (207) then generates a waveform encoded data stream by encoding data values of the second subband signal. The conversion processor (205) generates the second subband signal by direct subband conversion without converting back to the time domain. The invention allows an oversampled subband signal typically generated in parametric encoding to be waveform encoded with reduced complexity. A decoder performs the inverse operation.