Combined Innovation Codebook for Scalable CELP Audio Coding
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Solution Overview
Problem
ACELP innovation codebooks do not achieve significant quality gains at higher bit rates compared to other approaches like transform coding and vector quantization, and lack control over bit allocation across frequency components at higher bit rates.
Innovation Solution
A combined innovation codebook structure is introduced, comprising a first decoding stage operating in the frequency domain using a pre-quantizer with a pre-emphasis filter, DCT, and an Algebraic Vector Quantizer, followed by a second stage operating in the time domain with an ACELP innovation-codebook search, to enhance coding efficiency and scalability at higher bit rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ACELP innovation codebook is used, then coding efficiency is maintained at lower bit rates, but quality gains are not achieved at higher bit rates
Solution Approach 1:
The innovation codebook is divided into two separate codebooks: a first innovation codebook for lower bit rates and a second innovation codebook for higher bit rates. This segmentation allows each codebook to be optimized for its specific bit rate range, with the first codebook maintaining ACELP efficiency at lower rates and the second codebook providing transform coding quality at higher rates.
Solution Approach 2:
The system dynamically switches between the first and second innovation codebooks based on the available bit rate. At lower bit rates, the ACELP-based first codebook is used, while at higher bit rates, the transform coding-based second codebook is activated, allowing the system to adapt its coding strategy to achieve optimal quality across different operating conditions.
2Device complexity
If ACELP innovation codebook is used, then simplicity is maintained, but control over bit allocation across frequency components is lacking
Solution Approach 1:
The bit allocation control is segmented between two codebooks: the first ACELP codebook handles lower bit rates with simpler allocation, while the second transform coding codebook handles higher bit rates with fine-grained frequency-specific bit allocation control, allowing precise management of bits across different frequency components when needed.
Solution Approach 2:
The system changes the coding parameters and structure based on bit rate conditions. At higher bit rates where bit allocation control is needed, the second codebook uses transform coding parameters that enable frequency-specific bit allocation, while at lower bit rates, the simpler ACELP parameters are used to maintain efficiency.
Data Source
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AI summary
In a CELP coder, a combined innovation codebook coding device comprises a pre-quantizer of a first, adaptive-codebook excitation residual, and a CELP innovation-codebook search module responsive to a second excitation residual produced from the first, adaptive-codebook excitation residual. In a CELP decoder, a combined innovation codebook comprises a de-quantizer of pre-quantized coding parameters into a first excitation contribution, and a CELP innovation-codebook structure responsive to CELP innovation-codebook parameters to produce a second excitation contribution.