Audio Decoder High Frequency Reconstruction Metadata Extraction

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Solution Overview

Problem

Existing audio signal processing technologies, such as the MPEG-4 AAC standard, face challenges in efficiently reconstructing high frequency components of audio signals, particularly for musical content with low crossover frequencies, where spectral band replication techniques may not be ideal.

Innovation Solution

The method involves decoding an encoded audio bitstream, extracting high frequency reconstruction metadata, and filtering the decoded lowband audio signal using an analysis filterbank. A flag indicating whether spectral translation or harmonic transposition should be performed is extracted, and the highband portion of the audio signal is regenerated accordingly. The filtered lowband and regenerated highband signals are then combined to form a wideband audio signal.

Engineering Contradictions & Design Principles

VSEngineering 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 musical content with low crossover frequencies

Engineering Contradiction:

Improvecompression efficiencyVSAvoidaudio quality

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The patent implements dynamic selection between different HFR techniques (spectral translation and harmonic transposition) based on the characteristics of the audio content. The system adapts the reconstruction method to match the specific properties of the input signal, using spectral translation for speech-like content and harmonic transposition for musical content with low crossover frequencies, thereby optimizing both compression efficiency and audio quality for different content types

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the fundamental parameter of the HFR technique being applied by introducing a selection mechanism that switches between spectral translation and harmonic transposition. This parameter change allows the system to adjust the reconstruction approach based on audio content characteristics, resolving the contradiction between compression efficiency and audio quality for different types of content

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If enhanced HFR techniques like harmonic transposition are implemented, then audio quality is improved, but device complexity increases

Engineering Contradiction:

Improveaudio qualityVSAvoiddecoder complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent segments the HFR processing into distinct pathways: spectral translation for base HFR and harmonic transposition for enhanced HFR. The decoder structure is divided into separate processing blocks that can be independently implemented, allowing the selection of appropriate complexity levels based on content requirements without requiring the entire enhanced processing chain to be always active

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements partial action by allowing the decoder to activate only the necessary HFR technique based on content characteristics. For speech-like content, only spectral translation is applied, while harmonic transposition is activated only when needed for musical content, avoiding the constant overhead of full enhanced processing and reducing average device complexity

Inventive Principle:

Principle #16Partial or excessive action

3Ease of manufacture

If spectral patching is used for HFR, then implementation simplicity is maintained, but audio quality deteriorates for certain audio types

Engineering Contradiction:

Improveimplementation simplicityVSAvoidaudio quality

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent transforms the static spectral patching approach into a dynamic system that selects between spectral translation and harmonic transposition based on audio content analysis. This dynamic adaptation maintains implementation simplicity for speech-like content while improving audio quality for musical content through selective application of more sophisticated techniques

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS12296028B2Integration of high frequency reconstruction techniques with reduced post-processing delay

Publication Date: 2025.05.13 DOLBY INTERNATIONAL AB

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. The high frequency regeneration is performed as a post-processing operation with a delay of 3010 samples per audio channel.