Adaptive Time Resolution Audio Coding for Pre-Echo Suppression
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Solution Overview
Problem
Existing audio coding techniques, such as transform coders, face challenges in mitigating pre-echo artifacts, particularly in handling transients, due to increased complexity, bit-rate overhead, and delayed processing, which are not effectively addressed by current methodologies like bit reservoir techniques, gain modification, temporal noise shaping, and window switching.
Innovation Solution
The method involves using time-domain aliased frames for segmentation and spectral analysis, allowing for adaptive time segmentation and spectral analysis based on sub-frames, which enables instantaneous switching to higher time resolution and efficient bit-rate encoding, thereby mitigating pre-echo effects without the need for additional delay or increased complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If window switching is used to mitigate pre-echo artifacts, then pre-echo suppression is improved, but device complexity and processing delay increase
Solution Approach 1:
The patent applies dynamics by making the transform block size adaptive rather than fixed. The codec dynamically adjusts the block size between long and short blocks based on signal characteristics (transient detection), allowing optimal time resolution for pre-echo suppression while managing complexity through controlled variability in processing parameters
Solution Approach 2:
The patent segments the audio signal into different transform blocks (long and short blocks) with different time resolutions. By dividing the processing into segments with appropriate block sizes, the system can apply fine time resolution only where needed (transient regions) rather than uniformly across all signal portions, reducing overall complexity
2Object-affected harmful factors
If transform block size is reduced to enable temporal pre-masking, then pre-echo mitigation is improved, but coding gain decreases
Solution Approach 1:
The patent applies local quality by using different transform block sizes for different portions of the signal. Short blocks with fine time resolution are used locally in transient regions where pre-echo occurs, while long blocks with coarse time resolution are used in stationary regions to maintain coding gain. This localized adaptation optimizes both pre-echo suppression and compression efficiency
3Object-affected harmful factors
If bit reservoir technique is used to accommodate transient frames, then transient handling is improved, but transmission delay increases
Solution Approach 1:
The patent uses dynamics by adaptively adjusting transform block size in real-time based on transient detection, rather than using bit reservoir buffering. This allows the system to handle transients immediately with appropriate fine time resolution, avoiding the delay inherent in buffering approaches while still accommodating transient frames effectively
Data Source
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AI summary
The signal processing is based on the concept of using a time-domain aliased (12, TDA) frame as a basis for time segmentation (14) and spectral analysis (16), performing segmentation in time based on the time-domain aliased frame and performing spectral analysis based on the resulting time segments. The time resolution of the overall "segmented" time-to-frequency transform can thus be changed by simply adapting the time segmentation to obtain a suitable number of time segments based on which spectral analysis is applied. The overall set of spectral coefficients, obtained for all the segments, provides a selectable time-frequency tiling of the original signal frame.