Sound Encoder Nonlinear Transform for Quantization
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Solution Overview
Problem
Conventional speech coding methods increase bit rate due to the need to encode selection information for quantizer selection, which affects quantization performance.
Innovation Solution
A speech coding apparatus with a layered structure that analyzes the spectrum of a decoded signal, selects a nonlinear transform function based on the degree of variation, and uses inverse transforms to minimize bit rate and improve quantization performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a quantizer is selected according to the distribution of the signal which is a quantization target, then quantization performance is improved, but bit rate increases due to selection information
Solution Approach 1:
The patent extracts only the essential selection information (standard deviation values) from the quantizer selection process, transmitting only the necessary parameters rather than complete quantizer identification data. This reduces the bit rate overhead while maintaining the ability to select appropriate quantizers based on signal distribution characteristics.
Solution Approach 2:
The standard deviation calculation serves multiple functions: it characterizes the signal distribution for quantizer selection, provides scaling information for quantization, and enables adaptive quantization without requiring separate signaling mechanisms. This multi-functionality eliminates the need for additional selection information transmission.
2Measurement precision
If selection information is transmitted to indicate which quantizer is selected, then quantization performance is improved, but device complexity increases
Solution Approach 1:
The patent changes the parameter used for quantizer selection from complex distribution characteristics to a simple standard deviation value. This single parameter effectively characterizes the signal distribution and enables quantizer selection without complex encoding/decoding of selection information, reducing device complexity while maintaining quantization performance.
3Measurement precision
If transform coding is performed on residual signal, then sound quality is improved, but bit rate increases
Solution Approach 1:
The patent applies different quantization strategies to different parts of the spectrum based on local characteristics (standard deviation values). By adapting the quantization approach to local signal properties rather than using a uniform approach, efficient bit allocation is achieved that improves sound quality without proportionally increasing bit rate.
Data Source
AI summary
A sound encoder having an improved quantization performance while suppressing an increase of the bit rate to a lowest level. In a second layer encoder, a standard deviation calculator calculates a standard deviation σc of a first layer decoding spectrum after decoding a scale factor ratio multiplication and outputs the standard deviation σc to a selector. The selector selects a linear transform function as a function for a nonlinear transform of a residual spectrum according to the standard deviation σc A nonlinear transform function selects one of prepared nonlinear transform functions #1 to #N according to a result of the selection by the selector, and outputs the selected one to an inverse transformer. The inverse transformer subjects an inverse transform (expansion) to a residual spectrum candidate that is stored in a residual spectrum code book using the nonlinear transform function outputted from the nonlinear transform function and outputs the result to an adder.