Spectral Tilt Controlled Framing for Audio Bandwidth Extension
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In audio coding/decoding with bandwidth extension, existing technologies struggle to accurately detect energy shifts from low to high frequency portions, particularly in the presence of sibilants, leading to decreased quality of the reconstructed audio signal due to inadequate time resolution in spectral envelope data.
Innovation Solution
A spectral tilt detector is employed to identify energy shifts, signaling a start time instant for bandwidth extension parameter calculation, allowing for frame-wise adjustment of bandwidth extension parameters, which improves the accuracy of audio signal reconstruction by aligning with psycho-acoustic post-masking effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spectral envelope data is generated using fixed block-based processing, then the coding structure is simple and processing is efficient, but the time resolution is insufficient to accurately detect energy shifts from low to high frequency portions
Solution Approach 1:
The patent applies dynamics by making the frame structure adaptive rather than fixed. The framing is dynamically adjusted based on detected spectral tilt events, allowing the system to switch between different frame lengths and boundaries to match the temporal characteristics of the audio signal. This enables accurate detection of energy shifts while maintaining processing efficiency through event-driven framing.
Solution Approach 2:
The patent employs preliminary action by detecting spectral tilt events and identifying energy shift boundaries before generating spectral envelope data. The system pre-processes the signal to detect when energy shifts occur, then uses these detected boundaries to frame the spectral envelope coding. This ensures that the framing is aligned with actual signal characteristics rather than arbitrary fixed boundaries.
2Measurement precision
If the frame length is extended to improve detection accuracy of spectral tilts, then the time resolution improves, but the processing delay increases which is particularly problematic for mobile devices
Solution Approach 1:
The patent applies segmentation by dividing the audio signal into variable-length frames based on detected spectral tilt events rather than using uniform fixed-length frames. When energy shifts are detected, the system creates shorter frames to capture the transient behavior, while using longer frames during stable periods to improve spectral resolution. This segmented approach reduces processing delay while maintaining detection accuracy.
Solution Approach 2:
The patent changes the parameter of frame length dynamically based on signal characteristics. The system adjusts frame boundaries and lengths according to detected spectral tilt events, transitioning between different framing configurations to optimize the balance between detection accuracy and processing delay. This parameter adaptation allows the system to respond to varying signal conditions in real-time.
3Manufacturing precision
If bandwidth extension parameters are calculated with high time resolution, then the quality of audio signal reconstruction improves, but the processing resources required increase significantly
Solution Approach 1:
The patent applies local quality by applying high-time-resolution processing only locally at regions where spectral tilt events are detected, rather than uniformly across the entire audio signal. The system identifies specific time regions where energy shifts occur and applies detailed spectral envelope coding only to these localized regions, while using coarser coding in stable regions. This reduces overall processing resources while maintaining high reconstruction quality where it matters most.
Solution Approach 2:
The patent employs partial action by applying full-resolution bandwidth extension parameter calculation only partially - specifically during detected spectral tilt events - rather than continuously. The system uses reduced-resolution or simplified processing during normal periods, and switches to full-resolution processing only when energy shifts are detected. This partial application of high-resolution processing reduces computational load while maintaining audio quality during critical transient regions.
Data Source
AI summary
An apparatus for calculating bandwidth extension data of an audio signal in a bandwidth extension system, in which a first spectral band is encoded with a first number of bits and a second spectral band different from the first spectral band is encoded with a second number of bits, the second number of bits being smaller than the first number of bits, has a controllable bandwidth extension parameter calculator for calculating bandwidth extension parameters for the second frequency band in a frame-wise manner for a sequence of frames of the audio signal. Each frame has a controllable start time instant. The apparatus additionally includes a spectral tilt detector for detecting a spectral tilt in a time portion of the audio signal and for signaling the start time instant for the individual frames of the audio signal depending on spectral tilt.