High-Frequency Bandwidth Extension Coding With Energy Envelope Control
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Solution Overview
Problem
Current audio coding technologies face limitations in efficiently extending the bandwidth of high-frequency bands, particularly in spectral band replication (SBR), where high-frequency signals are less sensitive to frequency structure, leading to inadequate bit allocation and reduced coding efficiency.
Innovation Solution
A method and apparatus that includes a down-sampler, core coder, frequency transformer, and extension coder to perform bandwidth extension coding by generating a base signal in the frequency domain, estimating an energy control factor, extracting and quantizing energy, and applying an envelope to an artificial high-frequency signal, using techniques like multi-stage vector quantization and frequency weighting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If spectral band replication (SBR) is used to code high-frequency signals with an envelope, then coding efficiency is increased, but the resolution with regard to high-frequency signal structure is reduced
Solution Approach 1:
The patent segments the high-frequency band into multiple sub-bands and applies different coding strategies to each sub-band. Specifically, it divides the frequency spectrum into low-frequency and high-frequency portions, applying envelope coding to some regions while preserving fine spectral structure in others, thereby resolving the contradiction between overall coding efficiency and localized spectral resolution.
Solution Approach 2:
The patent applies local quality by using different coding approaches for different frequency regions. It identifies specific frequency ranges where fine structure preservation is critical and applies full-spectrum coding to those regions, while using envelope-based SBR coding in regions where it is less critical, thus maintaining high-frequency signal structure resolution where needed while preserving overall coding efficiency.
2Productivity
If a large number of bits are assigned to the low-frequency band, then coding efficiency is increased, but the bandwidth extension capability of the high-frequency band is limited
Solution Approach 1:
The patent transitions from time-domain coding to frequency-domain coding by applying Fourier transform to the input signal. This dimensional change enables effective bandwidth extension in the frequency domain while maintaining efficient bit allocation in the time domain, allowing simultaneous achievement of coding efficiency and high-frequency bandwidth extension.
Solution Approach 2:
The patent introduces an intermediary frequency-domain representation as a bridge between the time-domain signal and the extended high-frequency output. By transforming to frequency domain, processing the spectral components, and then transforming back, the system enables bandwidth extension without directly competing for bit allocation with the low-frequency band.
3Adaptability or versatility
If spectral band replication is used for high-frequency coding, then bit allocation restrictions are eliminated, but the high-frequency signal representation remains low resolution
Solution Approach 1:
The patent dynamically adjusts the coding strategy based on the characteristics of the input signal. It analyzes the spectral content and determines which frequency regions benefit most from fine structure preservation versus envelope-based coding, applying adaptive bit allocation that responds to signal dynamics rather than using a fixed low-resolution approach throughout.
Data Source
AI summary
A method and apparatus for performing coding and decoding for high-frequency bandwidth extension. The coding apparatus may classify a coding mode of a low-frequency signal of an input signal based on characteristics of the low-frequency signal of an input signal, perform code excited linear prediction coding or audio coding on the LPC excitation signal of the low-frequency signal of an input signal, and perform time-domain (TD) extension coding or frequency-domain (FD) extension coding on a high-frequency signal of an input signal. When the FD extension coding is performed, the coding apparatus may generate a base excitation signal for a high band using an input spectrum, obtain an energy control factor of a sub-band in a frame using the base excitation signal and the input spectrum, generate an energy signal based on the input spectrum and the energy control factor, for the sub-band in the frame, and quantize the energy signal.