Audio Signal Encoding State Initialization for Hybrid Coding
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Solution Overview
Problem
Hybrid-type audio coding schemes face challenges in initializing the adaptive codebook for CELP coding when switching from non-linear predictive coding schemes, leading to degradation in speech quality due to the lack of excitation signals from previous coding processes.
Innovation Solution
An audio signal encoding and decoding method that initializes the internal state of the linear predictive coding unit using residual signals and coefficients from previous frames, allowing seamless switching between different coding schemes and maintaining high coding efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If switching from non-CELP coding scheme to CELP coding scheme is performed without initializing the adaptive codebook, then coding scheme flexibility is improved, but speech quality degradation occurs due to lack of excitation signal information
Solution Approach 1:
The patent applies preliminary action by initializing the adaptive codebook with excitation signals from the previous frame before switching to CELP coding scheme. This preparation ensures that the encoding unit has the necessary excitation signal information ready, preventing speech quality degradation while maintaining coding scheme flexibility.
Solution Approach 2:
The patent uses an intermediary approach by introducing a buffer that stores excitation signals from non-CELP coded frames. This buffer acts as a mediator to transfer excitation signal information between different coding schemes, enabling seamless switching without loss of speech quality.
2Device complexity
If the adaptive codebook is not initialized when switching coding schemes, then device complexity is reduced, but coding efficiency decreases for frames immediately following the switch
Solution Approach 1:
The patent implements preliminary action by pre-initializing the adaptive codebook with excitation signals from the previous frame before the actual encoding operation. This advance preparation ensures high coding efficiency for frames immediately following the scheme switch without significantly increasing device complexity.
Solution Approach 2:
The patent applies self-service by having the encoding unit utilize its own previous frame's excitation signals to initialize the adaptive codebook. This self-initialization mechanism maintains coding efficiency while avoiding the need for external intervention or complex initialization procedures.
3Loss of information
If excitation signal information is not preserved during coding scheme switching, then information loss is minimized, but speech quality deteriorates due to lack of contextual information
Solution Approach 1:
The patent introduces a buffer as an intermediary to preserve excitation signal information from non-CELP coded frames. This buffer acts as a memory medium that maintains contextual information about excitation signals, preventing information loss and ensuring high speech quality during coding scheme transitions.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining the excitation signal information across coding scheme boundaries. The buffer stores excitation signals from previous frames, creating a continuous flow of relevant information that prevents abrupt degradation in speech quality when switching between coding schemes.
Data Source
AI summary
When a frame immediately preceding an encoding target frame to be encoded by a first encoding unit operating under a linear predictive coding scheme is encoded by a second encoding unit operating under a coding scheme different from the linear predictive coding scheme, the encoding target frame can be encoded under the linear predictive coding scheme by initializing the internal state of the first encoding unit. Therefore, encoding processing performed under a plurality of coding schemes including the linear predictive coding scheme and a coding scheme different from the linear predictive coding scheme can be realized.