High-Frequency Bandwidth Extension for Adaptive Audio Coding
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Solution Overview
Problem
Current audio coding technologies face challenges in efficiently extending the bandwidth of high-frequency bands, particularly in Spectral Band Replication (SBR), where the coding efficiency is limited by the allocation of bits to low-frequency and high-frequency bands, leading to suboptimal performance in representing high-frequency signals.
Innovation Solution
A method and apparatus for coding an audio signal that generates a base signal from a low-frequency band to extend the high-frequency band, using a combination of core coding and bandwidth extension techniques, including frequency-domain coding and multi-stage vector quantization, to allocate bits effectively across frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large number of bits are assigned to the low-frequency band to improve coding efficiency, then the low-frequency signal quality is improved, but the high-frequency band representation deteriorates due to bit allocation limitations
Solution Approach 1:
The patent applies spectral band replication by copying the low-frequency spectrum to generate the high-frequency spectrum. The low-frequency band signal is replicated and transformed to synthesize the high-frequency band, allowing efficient representation of high-frequency content without requiring additional bits for direct encoding of high-frequency details
Solution Approach 2:
Instead of directly encoding high-frequency signals with limited bits, the patent inverts the approach by synthesizing high-frequency content from low-frequency information. The high-frequency band is generated by replicating and transforming the low-frequency spectrum, rather than attempting to directly represent high-frequency details with insufficient bit allocation
2Length of moving object
If spectral band replication is used to extend high-frequency bands, then bandwidth extension is achieved, but coding efficiency is limited by the envelope-based representation of high-frequency signals
Solution Approach 1:
The patent changes the representation parameters of high-frequency signals by using multiple coding schemes with different parameter sets. Different coding schemes are selected based on the characteristics of the high-frequency signal, allowing optimization of coding efficiency for different signal types while maintaining bandwidth extension capabilities
Solution Approach 2:
The patent introduces dynamic selection of coding schemes based on signal characteristics. The encoder dynamically chooses between different coding approaches (e.g., different envelope representations or spectral models) depending on the actual high-frequency content, making the coding system adaptive rather than static
Data Source
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AI summary
Disclosed are an apparatus and a method for encoding/decoding for high-frequency bandwidth extension. The coding method comprises determining a core coding mode of a low-frequency signal of an input signal, based on characteristics of the low-frequency signal of the input signal, quantizing a linear prediction coefficient (LPC) from the low-frequency signal of the input signal. The method includes performing code excited linear prediction (CELP) coding on an LPC excitation signal of the low-frequency signal of the input signal when the core coding mode of the low-frequency signal of the input signal is determined to be a CELP coding mode. The method includes performing time-domain (TD) extension coding on a high-frequency signal of the input signal when the CELP coding is performed on the LPC excitation signal. The method includes performing audio coding on the LPC excitation signal when the core coding mode of the low-frequency signal of the input signal is determined to be an audio coding mode. The method includes performing frequency-domain (FD) extension coding on the high-frequency signal of the input signal when the audio coding is performed on the LPC excitation signal.