Audio Decoder Band-Adaptive CELP Suppression
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Solution Overview
Problem
The existing CELP component suppressing method deteriorates sound quality by uniformly suppressing the CELP component across all bands, leading to a loss of sound quality improvement in bands with significant speech or music contributions.
Innovation Solution
A decoding and coding apparatus that dynamically adjusts the CELP component suppression based on the energy of the residual signal in each band, using orthogonal transformation and band selection to minimize distortion and enhance sound quality by adapting the suppression level in each frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If CELP component suppressing is performed uniformly across all bands, then sound quality is improved in bands with high CELP residual energy, but noise floor attenuation occurs in bands with low CELP residual energy
Solution Approach 1:
The patent applies local quality by dividing the frequency spectrum into multiple bands and applying different CELP suppressing coefficients to each band. The decoding apparatus identifies a first band where the degree of suppression is adjusted based on the second spectrum (transform coding result), and applies suppression only to this identified band rather than uniformly across all bands. This resolves the contradiction by locally adapting the suppression strength to match the characteristics of each frequency band.
Solution Approach 2:
The patent implements dynamics by making the CELP suppressing coefficient adaptive rather than fixed. The decoding apparatus dynamically adjusts the degree of suppression in the identified first band based on the energy distribution in the second spectrum. This allows the suppression level to change according to the signal characteristics, improving sound quality where needed while avoiding noise floor attenuation in bands where CELP coding already performs well.
2Productivity
If CELP coding is used for speech signal coding, then speech coding efficiency is improved, but sound quality degrades for music signal coding
Solution Approach 1:
The patent applies segmentation by combining CELP coding and transform coding in a layer structure, where each coding method handles different aspects of the audio signal. The decoding apparatus processes first coded data (CELP) and second coded data (transform coding) separately, then combines their results. This allows speech-like components to be efficiently coded by CELP while music-like components are handled by transform coding, resolving the contradiction between speech efficiency and music quality.
Solution Approach 2:
The patent implements parameter changes by modifying the CELP decoded signal through spectral suppression in the frequency domain. The decoding apparatus performs orthogonal transformation on the CELP decoded signal to obtain a spectrum, then adjusts the spectral parameters by applying a suppressing coefficient to reduce the CELP component in specific bands. This allows the system to adapt the CELP output to better match the original signal characteristics, improving overall sound quality.
3Measurement precision
If transform coding is performed on the CELP residual signal, then sound quality is improved, but the residual signal energy is large when coding music signals
Solution Approach 1:
The patent applies preliminary action by performing suppression of the CELP component before transform coding. The decoding apparatus first obtains the CELP decoded signal, then performs orthogonal transformation and applies spectral suppression to reduce the CELP component in the frequency domain. This preliminary suppression reduces the energy of the residual signal that needs to be coded by transform coding, making the overall process more efficient while maintaining sound quality improvement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves sound quality by preventing noise floor attenuation in bands with low CELP residual energy and enhancing sound quality in bands with high CELP residual energy, effectively combining CELP and transform coding in a layer structure.
Implementation Method 1
a first decoding section that performs an orthogonal transformation on a signal obtained by decoding the first coded data, to generate a first spectrum
Data Source
AI summary
Disclosed is a decoder capable of improving the sound quality of a decoded sound signal in an encoding method which combines speech encoding and music encoding in a hierarchical structure. A transform-encoding decoding unit (202) decodes transform-encoded data to generate a spectrum of a decoded transform-encoded signal. A band decision unit (203) uses the spectrum of the decoded transform-encoded signal to decide whether each of a plurality of bands in which frequency components of an input signal are divided constitute a first band in which a transform encoded pulse is not established or a second band in which said pulse is established. A CELP component suppression unit (207) suppresses the spectrum of a CELP decoded signal, which is the frequency component of a decoded signal of CELP encoded data, to the extent that suppression in the first band is weaker than suppression in the second band.