Audio Bandwidth Extension via Temporal Noise Shaping
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Solution Overview
Problem
Existing bandwidth extension techniques in speech and audio coding face limitations, such as high bit consumption, artifacts, and restricted temporal resolution, especially when dealing with multiple core coders and high-pitched speech, while lacking viability for low bit rates and switched systems.
Innovation Solution
A decoder device that generates temporally shaped noise signals in the time domain, transforms them into the frequency domain, and combines them with the decoded audio signal to extend bandwidth independently of the core coder, allowing for super wideband frequency ranges with high perceptual quality and lower bit consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If spectral band replication is used for bandwidth extension, then bandwidth extension is achieved, but temporal resolution is restricted and artifacts occur
Solution Approach 1:
The invention separates the bandwidth extension process into distinct stages: generating noise signals in the time domain with high temporal resolution, transforming them to the frequency domain, and then combining with the decoded signal. This segmentation allows each stage to optimize for its specific function, maintaining temporal resolution in the time domain while achieving bandwidth extension in the frequency domain.
Solution Approach 2:
The invention introduces noise signals as an intermediary element to bridge the gap between the decoded low-frequency signal and the desired high-frequency content. These noise signals serve as a carrier that, when shaped and combined, provide the missing bandwidth without directly copying or mirroring the original signal, thereby avoiding the temporal resolution limitations of spectral band replication.
2Adaptability or versatility
If multiple core coders are used in switched systems, then coding flexibility is improved, but switching artifacts occur and bandwidth extension viability is reduced
Solution Approach 1:
The bandwidth extension method is designed to be universally applicable to multiple core coders and coding schemes. By using a core coder independent approach that operates on the decoded signal regardless of its origin, the same bandwidth extension process can be applied across different coding modes, ensuring consistent performance and eliminating the need for separate bandwidth extension paths that would cause switching artifacts.
Solution Approach 2:
The invention changes the fundamental parameters of how bandwidth extension is achieved by using noise signal generation and temporal shaping rather than signal copying or filtering. This parameter change makes the process adaptable to different coding schemes and reduces sensitivity to switching between coders, as the noise-based approach does not depend on the specific characteristics of any single core coder.
3Manufacturing precision
If guided bandwidth extension is used, then HF-reconstruction control is improved, but bit consumption increases
Solution Approach 1:
The invention extracts only the essential parameters needed for noise signal generation and temporal shaping from the encoded signal, rather than transmitting full high-frequency information. By taking out only the critical envelope and spectral characteristics needed to shape the noise, the method achieves effective HF-reconstruction control with minimal additional bit consumption.
Solution Approach 2:
The invention uses noise signals as temporary, disposable carriers for bandwidth extension. These noise signals are generated, shaped, and combined in a computationally efficient manner without requiring complex processing or transmission of detailed HF information. The noise serves its purpose of extending bandwidth and then can be discarded, providing an economical solution compared to transmitting and reconstructing full HF signal data.
Data Source
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AI summary
The invention provides an audio decoder device for decoding a bitstream, the audio decoder device comprising: a bitstream receiver configured to receive the bitstream and to derive an encoded audio signal from the bitstream; a core decoder module configured for deriving a decoded audio signal in a time domain from the encoded audio signal; a temporal envelope generator configured to determine a temporal envelope of the decoded audio signal; a bandwidth extension module configured to produce a frequency domain bandwidth extension signal, wherein the bandwidth extension module comprises a noise generator configured to produce a noise signal in time domain, wherein the bandwidth extension module comprises a pre-shaping module configured for temporal shaping of the noise signal depending on the temporal envelope of the decoded audio signal in order to produce a shaped noise signal and wherein the bandwidth extension module comprises a time-to-frequency converter configured to transform the shaped noise signal into a frequency domain noise signal; wherein the frequency domain bandwidth extension signal depends on the frequency domain noise signal; a time-to-frequency converter configured to transform the decoded audio signal into a frequency domain decoded audio signal; a combiner configured to combine the frequency domain decoded audio signal and the frequency domain bandwidth extension signal in order to produce a bandwidth extended frequency domain audio signal; and a frequency-to-time converter configured to transform the bandwidth extended frequency domain audio signal into a bandwidth-extended time domain audio signal.