Adaptive LPC Quantization Path Selection for Sound Encoding
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Solution Overview
Problem
Existing sound encoding systems face challenges in efficiently quantizing Linear Predictive Coding (LPC) coefficients due to their large dynamic range and sensitivity to quantization errors, particularly when rapid changes in sound frequency characteristics occur, leading to decreased quantization performance.
Innovation Solution
An apparatus that determines the optimal quantization path between using inter-frame prediction and not using it, employing either a first or second quantization scheme based on specific criteria, to efficiently quantify LPC coefficients, and includes a de-quantization path determination unit for accurate decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If inter-frame prediction is used for quantizing LSF coefficients, then quantization gain is improved by utilizing high inter-frame correlation, but quantization performance decreases when frequency characteristics change rapidly
Solution Approach 1:
The patent applies dynamics by making the quantization method adaptive rather than fixed. The system dynamically switches between two quantization paths based on the actual characteristics of the input signal: using inter-frame prediction when frames are similar (high correlation) and switching to independent quantization when frames differ significantly (rapid frequency changes). This dynamic adaptation resolves the contradiction by allowing the system to optimize for quantization gain under stable conditions while maintaining reliability when conditions change rapidly.
Solution Approach 2:
The patent changes the parameter of quantization methodology based on signal characteristics. By introducing a determination unit that evaluates frame similarity and selects appropriate quantization paths, the system adjusts its operating parameters (inter-frame prediction vs. independent quantization) to match the current state of the signal, thereby resolving the trade-off between quantization gain and performance reliability.
2Device complexity
If LPC coefficients are quantized directly, then the process is simple, but the stability of the LPC filter is not guaranteed due to large dynamic range and sensitivity to quantization errors
Solution Approach 1:
The patent introduces LSF coefficients as an intermediary representation between the original LPC coefficients and the quantized values. By transforming LPC coefficients to LSF coefficients before quantization, the system achieves better quantization characteristics and filter stability. The LSF coefficients serve as a mediator that preserves the essential spectral information while being more robust to quantization errors, thus resolving the contradiction between simple quantization and filter stability.
3Device complexity
If a single quantization path is used for all frames, then the device complexity is reduced, but the adaptability to varying sound characteristics is limited
Solution Approach 1:
The patent segments the quantization process into two distinct paths: one for frames with high inter-frame correlation (using inter-frame prediction) and another for frames with rapid frequency changes (using independent quantization). The determination unit acts as a router that directs each frame to the appropriate quantization path based on its characteristics. This segmentation allows the system to maintain low overall complexity while achieving high adaptability to varying sound characteristics.
Data Source
AI summary
A quantizing apparatus is provided that includes a quantization path determiner that determines a path from a first path not using inter-frame prediction and a second path using the inter-frame prediction, as a quantization path of an input signal, based on a criterion before quantization of the input signal; a first quantizer that quantizes the input signal, if the first path is determined as the quantization path of the input signal; and a second quantizer that quantizes the input signal, if the second path is determined as the quantization path of the input signal.