Adaptive Spectral Tile Filling for Low-Bitrate Audio Decoding

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Solution Overview

Problem

Current audio codecs face limitations in bandwidth extension techniques, particularly in maintaining high-frequency detail and timbre accuracy at low bitrates, due to restrictions in replacing perceptually important content above a given cross-over frequency and requiring transformation into new domains, which leads to computational complexity and synchronization issues.

Innovation Solution

The implementation of an Intelligent Gap Filling (IGF) scheme that adapts frequency tile filling, allowing for signal-dependent source region selection and processing, enabling efficient encoding and decoding in the same spectral domain without the need for downsampling or upsampling, and utilizing parametric data for spectral gap filling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If bandwidth extension techniques are used to reduce bitrate, then compression efficiency is improved, but high-frequency detail and timbre accuracy deteriorate

Engineering Contradiction:

Improvecompression efficiencyVSAvoidhigh-frequency detail accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent applies local quality by differentiating between tonal and non-tonal spectral regions. Tonal regions are preserved with high fidelity using waveform coding, while non-tonal regions use parametric coding. This localized approach ensures that perceptually important tonal components maintain their detail and timbre accuracy even at low bitrates, while achieving compression in non-critical regions.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The spectrum is segmented into multiple frequency tiles, with different coding strategies applied to different tiles. This segmentation allows the system to selectively apply bandwidth extension only where necessary, preserving high-frequency detail in tonal tiles while using compression in non-tonal tiles, thus resolving the contradiction between compression efficiency and frequency detail accuracy.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If spectral patching is used for bandwidth extension, then bandwidth extension capability is improved, but computational complexity increases

Engineering Contradiction:

Improvebandwidth extension capabilityVSAvoidcomputational complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent implements dynamic spectral selection where the source region for each target frequency tile is adaptively chosen based on spectral similarity metrics. This dynamic approach allows the system to efficiently identify matching spectral regions without exhaustive search, reducing computational complexity while maintaining versatile bandwidth extension capability across different audio signals.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system uses parametric representation of spectral regions and changes parameters such as spectral similarity thresholds and tile boundaries adaptively. This allows bandwidth extension to be achieved through parameter manipulation rather than complex signal processing operations, reducing computational complexity while preserving extension capability.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If transformation into new domains is performed for bandwidth extension, then bandwidth extension accuracy is improved, but synchronization issues arise

Engineering Contradiction:

Improvebandwidth extension accuracyVSAvoidsynchronization reliability

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent performs bandwidth extension within the same spectral domain (MDCT domain) used for the core audio coding, making the system multi-functional. This universal approach eliminates the need for separate transformation stages, thereby maintaining synchronization reliability while achieving accurate bandwidth extension through spectral replication and parametric synthesis in the unified domain.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Adaptability or versatility

If downsampling or upsampling is used in bandwidth extension, then bandwidth extension capability is improved, but computational complexity increases

Engineering Contradiction:

Improvebandwidth extension capabilityVSAvoidcomputational complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent extracts the essential spectral characteristics from the low-frequency region and directly synthesizes the high-frequency content through parametric modeling and spectral replication. This extraction approach avoids the need for time-consuming downsampling/upsampling operations, reducing computational complexity while maintaining bandwidth extension capability through intelligent spectral synthesis.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS10984805B2Apparatus and method for decoding and encoding an audio signal using adaptive spectral tile selection

Publication Date: 2021.04.20 FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV

AI summary

An apparatus for decoding an encoded signal includes: an audio decoder for decoding an encoded representation of a first set of first spectral portions to obtain a decoded first set of first spectral portions; a parametric decoder for decoding an encoded parametric representation of a second set of second spectral portions to obtain a decoded representation of the parametric representation, wherein the parametric information includes, for each target frequency tile, a source region identification as a matching information; and a frequency regenerator for regenerating a target frequency tile using a source region from the first set of first spectral portions identified by the matching information.