Interleaved Waveform Audio Coding for High-Frequency Transients
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Solution Overview
Problem
Existing audio coding systems, such as the MPEG-4 standard's SBR algorithm, struggle with the reconstruction of strong tonal components and transients in high frequency bands, leading to issues like missing harmonics and transient smearing, especially at low bitrates.
Innovation Solution
An encoder and decoder system that uses waveform coding for specific frequency ranges above a crossover frequency, interleaving this with high frequency reconstruction to improve the reconstruction of tonal components and transients, utilizing sparse frequency intervals and adjusting spectral envelopes to optimize bit usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If SBR algorithm is used for high frequency reconstruction, then bitrate is reduced, but tonal components and transients are poorly reconstructed
Solution Approach 1:
The patent segments the high frequency spectrum into multiple sub-bands and applies different coding strategies to each sub-band. Specifically, it identifies sub-bands containing tonal components or transients and applies waveform coding to those sub-bands while using SBR for other sub-bands, thereby preserving important signal features while maintaining bitrate efficiency.
Solution Approach 2:
The patent applies local quality by treating different frequency sub-bands differently based on their characteristics. Sub-bands containing tonal components or transients receive waveform coding for high fidelity, while sub-bands without such features use SBR for compression, ensuring that critical signal elements are preserved with high quality.
2Manufacturing precision
If waveform coding is applied to all frequency bands, then reconstruction accuracy is improved, but bitrate increases
Solution Approach 1:
The patent divides the frequency spectrum into low frequency bands (coded with waveform coding) and high frequency sub-bands (coded with a combination of SBR and selective waveform coding). This segmentation allows waveform coding to be applied only where necessary for tonal and transient preservation, rather than across the entire spectrum.
Solution Approach 2:
The patent applies waveform coding partially - only to specific sub-bands that contain tonal components or transients, rather than to all high frequency content. This partial application of waveform coding achieves the necessary reconstruction accuracy for critical features while avoiding the excessive bitrate cost of applying it universally.
3Manufacturing precision
If missing harmonics detection is implemented, then tonal components are preserved, but device complexity increases
Solution Approach 1:
The patent segments the high frequency range into multiple sub-bands and applies missing harmonics detection and waveform coding selectively to specific sub-bands based on their spectral characteristics. This segmentation reduces the overall complexity compared to applying the full detection and coding process to the entire high frequency range.
Data Source
AI summary
There is provided methods and apparatuses for decoding and encoding of audio signals. In particular, a method for decoding includes receiving a waveform-coded signal having a spectral content corresponding to a subset of the frequency range above a cross-over frequency. The waveform-coded signal is interleaved with a parametric high frequency reconstruction of the audio signal above the cross-over frequency. In this way an improved reconstruction of the high frequency bands of the audio signal is achieved.