Audio Decoder Context Adaptation for Pitch Variations
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Solution Overview
Problem
Audio signal encoding and decoding techniques face inefficiencies when dealing with variations in fundamental frequency or pitch, leading to reduced coding efficiency, especially in the presence of time-varying pitch patterns.
Innovation Solution
An audio signal decoder and encoder that adapt the context state to changes in fundamental frequency between audio frames, using time warp information to improve coding efficiency by exploiting similarities and frequency scaling in spectral representations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a fixed context model is used for spectral value decoding, then the decoder complexity is low, but coding efficiency deteriorates when fundamental frequency varies between frames
Solution Approach 1:
The context model is made dynamic by adapting it to pitch variations between frames. The context state is scaled based on the ratio of fundamental frequencies between current and previous frames, allowing the decoder to adjust to changing spectral characteristics while maintaining reasonable complexity through a systematic adaptation rule rather than complete re-modeling
Solution Approach 2:
The context state parameters are modified according to the fundamental frequency ratio. Specifically, the context state is scaled by a factor derived from the pitch variation, which changes the decoding behavior to match the current spectral distribution without requiring a completely new context model
2Productivity
If time warping is applied to handle pitch variations, then spectral energy compaction improves, but additional side information is required at the decoder
Solution Approach 1:
The decoder uses the already-transmitted time warp information (describing pitch contour) to adapt its own context model. Instead of requiring separate side information for context adaptation, the system makes the decoder self-sufficient by deriving the necessary adaptation parameters from the existing time warp data that describes the pitch variations
3Productivity
If context adaptation to pitch variation is implemented, then coding efficiency improves, but computational complexity increases
Solution Approach 1:
The context adaptation is applied locally to the arithmetic decoder's context state rather than globally to the entire decoding process. The adaptation is focused specifically on scaling the context state based on pitch ratio, leaving other decoding operations unchanged and minimizing the increase in computational complexity
Data Source
AI summary
An audio signal decoder includes a context-based spectral value decoder configured to decode a codeword describing one or more spectral values or at least a portion of a number representation thereof in dependence on a context state. The audio signal decoder also includes a context state determinator configured to determine a current context state in dependence on one or more previously decoded spectral values and a time warping frequency-domain-to-time-domain converter configured to provide a time-warped time-domain representation of a given audio frame on the basis of a set of decoded spectral values provided by the context-based spectral value decoder and in dependence on the time warp information. The context-state determinator is configured to adapt the determination of the context state to a change of a fundamental frequency between subsequent audio frames. An audio signal encoder applies a comparable concept.