Spectrum Coding Apparatus Harmonic Structure Preservation
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Solution Overview
Problem
Conventional coding technologies distort the harmonic structure of voice and audio signals when compressing them to low bit rates, leading to a deterioration in sound quality due to the lack of consideration for the shape of the harmonic structure during the replacement of high-frequency spectra with low-frequency spectra.
Innovation Solution
A coding apparatus and method that acquire spectra divided into low-frequency and high-frequency bands, calculate a parameter indicating the degree of similarity between the two based on the harmonic structure, and encode this parameter instead of the high-frequency spectrum, ensuring that the harmonic structure is maintained during coding and decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the spectrum of the high-frequency domain is replaced by the spectrum of the low-frequency domain to reduce bit rate, then the bit rate is reduced, but the harmonic structure is collapsed and sound quality deteriorates
Solution Approach 1:
The patent changes the parameter representation from direct spectrum values to parameters indicating the degree of similarity between low-frequency and high-frequency spectra. This allows the high-frequency spectrum to be reconstructed from the low-frequency spectrum using the similarity parameter, thereby reducing bit rate while preserving the harmonic structure through parameter-based transformation rather than direct replacement
Solution Approach 2:
The patent creates a simplified copy of the high-frequency spectrum by using the low-frequency spectrum and a similarity parameter. Instead of transmitting the full high-frequency spectrum, a parameter indicating the degree of similarity is transmitted, which allows the receiver to reconstruct the high-frequency spectrum by copying and transforming the low-frequency spectrum according to the similarity parameter, thus reducing bit rate while maintaining harmonic structure
2Manufacturing precision
If wideband signals are used as coding targets to improve sound quality, then sound quality improves, but the bit rate increases
Solution Approach 1:
The patent extracts only the essential information needed for high-quality wideband coding by separating the spectrum into low-frequency and high-frequency domains. It extracts the low-frequency spectrum and a parameter indicating the degree of similarity to represent the high-frequency spectrum, thereby extracting only the necessary information components to achieve wideband quality while minimizing bit rate
Solution Approach 2:
The patent segments the wideband signal into low-frequency and high-frequency domains, then applies different coding strategies to each segment. The low-frequency spectrum is coded directly while the high-frequency spectrum is represented by a similarity parameter relative to the low-frequency spectrum, allowing efficient segmentation-based coding that achieves wideband quality at lower bit rates
Data Source
AI summary
A coding apparatus capable of coding a spectrum at a low bit rate and with high quality without producing any disturbance in a harmonic structure of the spectrum. In this apparatus, internal state setting section sets an internal state of a filtering section using a first spectrum S1(k). A pitch coefficient setting section outputs a pitch coefficient T by gradually changing it. The filtering section calculates an estimated value S′2(k) of a second spectrum S2(k) based on a pitch coefficient T. A search section calculates the degree of similarity between S2(k) and S′2(k). At this time, pitch coefficient T′ corresponding to the maximum calculated degree of similarity is given to a filter coefficient calculation section. The filter coefficient calculation section determines a filter coefficient βi using this pitch coefficient T′.