Bandwidth Extension Decoder Using Offset Frequency Matching

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Solution Overview

Problem

Existing bandwidth extension methods for audio signals, especially at low bit rates, suffer from high complexity and poor audio quality due to inadequate maintenance of harmonic relations between low and high-frequency bands, leading to artifacts like roughness and unpleasant timbre.

Innovation Solution

A bandwidth extension decoder and encoder system that generates and compares bandwidth extension high-frequency signals with different offset frequencies, calculating comparison parameters to determine an optimal offset frequency and power density parameter, allowing for improved audio quality and reduced bit rate by reconstructing the high-frequency band using these parameters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If bandwidth extension methods are used to reduce bit rate, then transmission efficiency is improved, but audio quality deteriorates due to loss of harmonic relations

Engineering Contradiction:

Improvebit rateVSAvoidaudio quality

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The patent copies the low-frequency signal characteristics to generate high-frequency components through spectral replication. The low-frequency band signal is processed and replicated into the high-frequency band, creating a copied version that maintains the essential harmonic relationships while enabling bandwidth extension at reduced bit rates.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent applies parameter changes by modifying the spectral characteristics of the low-frequency signal to generate high-frequency components. Specifically, the system adjusts frequency scaling factors and spectral envelopes to transform the low-frequency content into high-frequency content that preserves harmonic relations, thereby improving audio quality while maintaining bit rate reduction.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If harmonic transposition with filterbank patching is used, then bandwidth extension is achieved, 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 harmonic relationship information from the low-frequency signal and uses this extracted information to generate high-frequency components. By separating and processing only the critical spectral envelope and frequency scaling parameters, the system avoids the computational burden of full filterbank operations while maintaining bandwidth extension capability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of generating high-frequency content first and then downmixing to low-frequency (as in traditional filterbank approaches), the patent inverts the process by starting with the low-frequency signal and synthesizing high-frequency content from it. This inversion simplifies the computational path while achieving the same bandwidth extension effect.

Inventive Principle:

Principle #13The other way round (Inversion)

3Device complexity

If simple copying of low-frequency signal is used, then computational complexity is reduced, but harmonic relations are not maintained causing artifacts

Engineering Contradiction:

Improvecomputational complexityVSAvoidaudio artifacts

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The patent applies parameter changes by introducing frequency scaling factors and spectral envelope adjustments to the simple copying process. These parameter modifications ensure that when low-frequency signal characteristics are replicated to high-frequency bands, the harmonic relationships are preserved, preventing artifacts like roughness and unpleasant timbre while keeping computational complexity low.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12475903B2Audio encoder and bandwidth extension decoder

Publication Date: 2025.11.18 FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV

AI summary

An audio encoder for providing an output signal using an input audio signal includes a patch generator, a comparator and an output interface. The patch generator generates at least one bandwidth extension high-frequency signal, wherein a bandwidth extension high-frequency signal includes a high-frequency band. The high-frequency band of the bandwidth extension high-frequency signal is based on a low frequency band of the input audio signal. A comparator calculates a plurality of comparison parameters. A comparison parameter is calculated based on a comparison of the input audio signal and a generated bandwidth extension high-frequency signal. Each comparison parameter of the plurality of comparison parameters is calculated based on a different offset frequency between the input audio signal and a generated bandwidth extension high-frequency signal. Further, the comparator determines a comparison parameter from the plurality of comparison parameters, wherein the determined comparison parameter fulfils a predefined criterion.