Audio Spectrum Reconstruction Using IGF Energy Bands
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Solution Overview
Problem
Current audio codecs face limitations in coding high-frequency content at low bitrates, leading to loss of detail and timbre, as they restrict bandwidth extension to replace only high-frequency content and do not accurately align tonal harmonics, requiring transformation into new domains which increases computational complexity and memory requirements.
Innovation Solution
The Intelligent Gap Filling (IGF) method reconstructs spectral values by using frequency tiles from tonal portions in lower frequency ranges, allowing full-rate core decoding and encoding across the entire audio spectrum, filling spectral gaps with parametric data and source spectral ranges, and applying frequency regeneration to maintain energy accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bandwidth extension is used to code high-frequency content at low bitrates, then compression efficiency is improved, but audio quality deteriorates due to loss of detail and timbre
Solution Approach 1:
The patent segments the frequency spectrum into multiple reconstruction bands and processes each band separately using energy information values. This allows selective reconstruction of high-frequency content while preserving perceptually important tonal portions, thereby maintaining audio quality while achieving compression efficiency.
Solution Approach 2:
The patent applies different reconstruction strategies to different frequency regions based on their perceptual importance. Tonal portions are preserved with higher fidelity while noise-like regions are reconstructed using parametric data, optimizing the balance between compression and quality locally across the spectrum.
2Adaptability or versatility
If spectral patching is used to reconstruct high-frequency regions, then bandwidth extension is achieved, but computational complexity increases due to transformation into new domains
Solution Approach 1:
The patent extracts only the essential energy information values from the original high-frequency signal and transmits them as parametric data. The actual spectral reconstruction is performed in the decoder using these compact parameters, avoiding the need for complex transformations and reducing computational complexity while maintaining bandwidth extension capability.
3Loss of substance
If high-frequency content is replaced with parametric data, then bitrate is reduced, but frequency alignment accuracy deteriorates
Solution Approach 1:
The patent uses dynamic scaling factors for each reconstruction band that are adapted to the local spectral characteristics. This allows the parametric reconstruction to dynamically align with the actual frequency content, maintaining frequency alignment accuracy even at low bitrates by adjusting the reconstruction parameters based on the energy information values.
Data Source
AI summary
An apparatus for decoding an encoded audio signal having an encoded representation of a first set of first spectral portions and an encoded representation of parametric data indicating spectral energies for a second set of second spectral portions, has: an audio decoder for decoding the encoded representation of the first set of the first spectral portions to obtain a first set of first spectral portions and for decoding the encoded representation of the parametric data to obtain a decoded parametric data for the second set of second spectral portions indicating, for individual reconstruction bands, individual energies; a frequency regenerator for reconstructing spectral values in a reconstruction band having a second spectral portion using a first spectral portion of the first set of the first spectral portions and an individual energy for the reconstruction band, the reconstruction band having a first spectral portion and the second spectral portion.