High-Frequency Audio Reconstruction With Backward-Compatible eSBR
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Solution Overview
Problem
The MPEG-4 AAC standard's spectral band replication (SBR) tool is not ideal for certain audio types, such as musical content with relatively low crossover frequencies, necessitating improvements in spectral band replication techniques for enhanced audio quality at low data rates.
Innovation Solution
The method involves decoding an encoded audio bitstream, extracting high frequency reconstruction metadata, filtering the lowband audio signal, and regenerating the highband portion using the metadata, with options for spectral translation or harmonic transposition based on a flag, to form a wideband audio signal, and includes enhanced spectral band replication (eSBR) processing using tools like harmonic transposition and QMF-patching for improved high frequency reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If spectral band replication (SBR) is used for high frequency reconstruction, then compression efficiency is improved, but audio quality deteriorates for certain audio types such as musical content with low crossover frequencies
Solution Approach 1:
The patent implements dynamic selection between different high frequency reconstruction methods (spectral translation vs. harmonic transposition) based on the characteristics of the audio signal. The system analyzes the audio content and adaptively chooses the appropriate reconstruction technique, allowing the decoder to optimize between compression efficiency and audio quality depending on the specific musical or speech content being processed.
Solution Approach 2:
The patent changes the reconstruction parameters by introducing a flag in the bitstream that indicates whether spectral translation or harmonic transposition should be used. This parameter change allows the system to switch between different reconstruction algorithms, with spectral translation providing better compression for speech and harmonic transposition providing superior audio quality for musical content with low crossover frequencies.
2Measurement precision
If enhanced spectral band replication (eSBR) tools like harmonic transposition are used, then high frequency reconstruction accuracy is improved, but decoder complexity increases
Solution Approach 1:
The patent implements dynamic selection between different high frequency reconstruction methods (spectral translation vs. harmonic transposition) based on the characteristics of the audio signal. The system analyzes the audio content and adaptively chooses the appropriate reconstruction technique, allowing the decoder to optimize between compression efficiency and audio quality depending on the specific musical or speech content being processed.
Solution Approach 2:
The patent changes the reconstruction parameters by introducing a flag in the bitstream that indicates whether spectral translation or harmonic transposition should be used. This parameter change allows the system to switch between different reconstruction algorithms, with spectral translation providing better compression for speech and harmonic transposition providing superior audio quality for musical content with low crossover frequencies.
3Manufacturing precision
If new high frequency reconstruction techniques are implemented, then audio quality is improved, but compatibility with existing decoding systems deteriorates
Solution Approach 1:
The patent implements a universal decoder architecture that can handle both traditional spectral translation and enhanced harmonic transposition methods. By incorporating a flag-based selection mechanism and making the harmonic transposition module optional, the decoder can function in multiple modes - operating as a legacy spectral translation decoder for compatibility, or as an enhanced eSBR decoder when the flag indicates harmonic transposition should be used.
Solution Approach 2:
The patent performs preliminary action by embedding a flag in the encoded audio bitstream that预先 indicates whether harmonic transposition should be used. This allows the decoder to prepare appropriately - if the flag indicates spectral translation, the decoder operates in legacy mode for compatibility; if the flag indicates harmonic transposition, the decoder activates the enhanced reconstruction module, thus preparing in advance for the required processing mode.
Data Source
AI summary
A method for decoding an encoded audio bitstream is disclosed. The method includes receiving the encoded audio bitstream and decoding the audio data to generate a decoded lowband audio signal. The method further includes extracting high frequency reconstruction metadata and filtering the decoded lowband audio signal with an analysis filterbank to generate a filtered lowband audio signal. The method also includes extracting a flag indicating whether either spectral translation or harmonic transposition is to be performed on the audio data and regenerating a highband portion of the audio signal using the filtered lowband audio signal and the high frequency reconstruction metadata in accordance with the flag.