Audio Bandwidth Extension Encoding Using High-Frequency Envelope Copying
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Solution Overview
Problem
Current audio encoding methods face inefficiencies in encoding high-frequency audio signals due to limited bit allocation, necessitating improved methods to enhance bandwidth extension in the high-frequency domain without compromising quality.
Innovation Solution
The proposed method involves extracting a basic signal from the input audio, controlling its energy based on tonality, and using this information to efficiently extend the high-frequency domain bandwidth through bandwidth extension encoding, which includes generating an artificial high-frequency signal by copying and folding the low-frequency signal, and quantizing energy using advanced techniques like Vector Quantization and frequency weighting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a large number of bits are allocated to low-frequency domain signals, then encoding quality of low-frequency signals is improved, but encoding efficiency for high-frequency domain signals deteriorates due to limited total bits
Solution Approach 1:
The patent applies local quality by differentiating encoding strategies for different frequency domains. Low-frequency signals receive detailed encoding with more bits allocated to preserve fine structure, while high-frequency signals use envelope-based encoding with fewer bits since human auditory resolution is lower in high bands. This localized approach to encoding quality resolves the contradiction by optimizing bit allocation according to perceptual importance rather than uniform distribution.
Solution Approach 2:
The patent uses copying by representing high-frequency component signals as envelopes that are synthesized during decoding. Instead of encoding full high-frequency spectral data, the system captures essential envelope characteristics and reconstructs the high-band signal during playback. This copying approach significantly reduces bit requirements for high-frequency encoding while maintaining perceptual quality, thereby improving overall encoding efficiency.
2Manufacturing precision
If bandwidth extension is applied to extend high-frequency domain from 6.4 kHz to 16 kHz, then audio quality is improved, but encoding complexity increases
Solution Approach 1:
The patent applies preliminary action by extracting and encoding essential high-frequency envelope characteristics during the encoding phase, which are then used to synthesize the full high-band signal during decoding. By preparing and transmitting only the critical envelope parameters in advance rather than complete spectral data, the system achieves bandwidth extension with reduced encoding complexity and computational requirements.
Solution Approach 2:
The patent uses an envelope signal as an intermediary between the original audio and the synthesized high-frequency components. The envelope captures the essential amplitude modulation characteristics of high-frequency signals, serving as a compact representation that enables reconstruction of the full bandwidth signal during decoding without requiring direct transmission of all high-frequency spectral details, thus reducing encoding complexity.
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AI summary
An apparatus and method for encoding and decoding a signal for high frequency bandwidth extension are provided. An encoding apparatus may down-sample a time domain input signal, may core-encode the down-sampled time domain input signal, may transform the core-encoded time domain input signal to a frequency domain input signal, and may perform bandwidth extension encoding using a basic signal of the frequency domain input signal.