Speech Coding LTP Codebook Segmentation
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Solution Overview
Problem
Existing speech encoding techniques, such as those using Linear Predictive Coding (LPC) and Code-Excited Linear Predictive (CELP) coding, face challenges in efficiently quantizing long-term prediction (LTP) coefficients, leading to high bitrate requirements and computational complexity due to the need for large codebooks and frequent updates.
Innovation Solution
The method employs multiple vector quantization codebooks to jointly quantize LTP coefficients, selecting the most efficient codebook based on rate-distortion trade-offs and using Entropy Constrained Vector Quantization, which reduces bitrate by using a single codebook indicator for all LTP vectors in a frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large codebooks are used for quantizing LTP coefficients, then quantization performance is improved, but bitrate and computational complexity increase
Solution Approach 1:
The patent divides the codebook into multiple subcodebooks, each handling specific portions of the LTP coefficient space. This segmentation allows the system to achieve comprehensive quantization coverage without requiring a single large codebook, thereby reducing memory requirements and computational complexity while maintaining quantization performance.
Solution Approach 2:
The patent implements dynamic codebook selection where the appropriate subcodebook is chosen based on the current speech frame characteristics. This dynamic approach allows the system to adapt to varying speech conditions, using only the necessary portions of the codebook structure, thus reducing average computational complexity and bitrate while preserving quantization accuracy when needed.
2Measurement precision
If large codebooks are used for quantizing LTP coefficients, then quantization performance is improved, but bitrate increases
Solution Approach 1:
By segmenting the codebook into multiple subcodebooks, the patent enables more efficient indexing and transmission. Instead of transmitting indices for a large monolithic codebook, the system transmits indices for smaller subcodebooks, reducing the overall bitrate required to achieve the same quantization performance.
Solution Approach 2:
The patent applies partial action by using only the necessary subcodebooks for each speech frame rather than the entire codebook structure. This selective approach transmits only the relevant quantization data, reducing bitrate while maintaining quantization performance for the actual speech content being encoded.
3Measurement precision
If codebooks are updated frequently, then encoding accuracy is improved, but computational complexity and storage needs increase
Solution Approach 1:
The patent segments the codebook structure into multiple subcodebooks that can be independently managed and updated. This segmentation allows the system to maintain accurate encoding by updating only the necessary subcodebooks rather than the entire codebook, thereby reducing storage requirements and computational overhead while preserving encoding accuracy.
Data Source
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AI summary
A method, system and program for encoding and decoding speech according to a source-filter model whereby speech is modelled to comprise a source signal filtered by a time-varying filter. The method comprises: receiving a speech signal; and from the speech signal, deriving a spectral envelope signal representing the modelled filter and a remaining signal representing the modelled source. At intervals during the encoding, the method further comprises determining a period between portions of the remaining signal having a degree of repetition and determining a correlation between said portions based on that period, thus producing a respective vector of the correlation for each interval. Once every number of said intervals, the method further comprises selecting a codebook from a plurality of codebooks for quantizing the vectors, quantizing the vectors of that number of intervals according to the selected codebook, and transmitting the quantized vectors along with an indication of the selected codebook.