SBR Encoder Grid Boundary Synchronization for Transient Handling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing audio encoding techniques using SBR (Spectral Band Replication) face challenges in minimizing bit rate while avoiding audible artefacts like pre-echo, particularly at transients, due to the need for a fine temporal grid that increases bit consumption.
Innovation Solution
Introducing a new SBR frame class, LD_TRAN, where frame boundaries are synchronized with grid boundaries, and using a transient position indication to determine grid boundaries, reducing the need for variable frame classes and minimizing bit transmission, allowing for shorter grid areas around transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a fine temporal grid is used to avoid audible artefacts at transients, then audio quality is improved, but bit rate increases
Solution Approach 1:
The patent applies local quality by using a fine temporal grid only in the neighborhood of transients while using a coarse grid elsewhere. The grid resolution is adaptively adjusted based on the presence and position of transients, allowing high resolution where needed (around transients) and low resolution where not needed (in stationary regions), thus resolving the contradiction between audio quality and bit rate.
Solution Approach 2:
The patent implements dynamics by making the temporal grid configuration variable rather than fixed. The grid boundaries are dynamically adjusted based on transient detection, allowing the system to switch between fine and coarse grid regions in real-time. This dynamic adaptation enables the system to optimize between audio quality and bit rate depending on the signal characteristics.
2Loss of substance
If the temporal grid is made coarse to reduce bit consumption, then bit rate is reduced, but audible artefacts appear at transients
Solution Approach 1:
The patent applies segmentation by dividing the audio signal into different temporal regions based on transient detection. The timeline is segmented into transient neighborhoods (requiring fine grid) and non-transient regions (allowing coarse grid). This segmentation enables the system to allocate computational and bit resources selectively, reducing overall bit rate while maintaining quality where needed.
Solution Approach 2:
The patent uses local quality by applying high temporal resolution only locally around transients rather than uniformly across the entire signal. The grid density is adapted to the local signal characteristics, using fine resolution where transients occur and coarse resolution in stationary regions, thus reducing average bit rate while preventing artefacts at critical locations.
3Reliability
If variable frame classes are used to handle transients, then transient handling is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing a single frame class (FIXFIX) that can handle multiple scenarios: normal stationary signals, transients at any position, and boundary cases. By making the frame structure universal and adaptable through parameter adjustment (grid boundaries, reconstruction modes) rather than creating multiple specialized classes, the system reduces complexity while maintaining reliable transient handling.
Solution Approach 2:
The patent uses parameter changes by adjusting frame parameters (grid boundaries, reconstruction modes, spectral envelope transmission) within a single frame class rather than switching between multiple frame classes. This parameter-based adaptation achieves transient handling flexibility without the complexity of managing multiple frame class types, resolving the contradiction between reliability and device complexity.
4Reliability
If grid boundaries are offset from frame boundaries to capture transients, then transient detection is improved, but decoding delay increases
Solution Approach 1:
The patent applies preliminary action by detecting transients and preparing the appropriate grid configuration in advance within the same frame, rather than waiting for the transient to occur or using future frames. The transient detection and grid adjustment are performed preliminarily within the current frame processing cycle, enabling timely response without requiring offset grid boundaries that would cause decoding delay.
Data Source
AI summary
The transient problem may be sufficiently addressed, and for this purpose, a further delay on the side of the decoding may be reduced if a new SBR frame class is used wherein the frame boundaries are not shifted, i.e. the grid boundaries are still synchronized with the frame boundaries, but wherein a transient position indication is additionally used as a syntax element so as to be used, on the encoder and/or decoder sides, within the frames of these new frame class for determining the grid boundaries within these frames.