SBR Frame Grid Alignment for Transient Audio Encoding

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Solution Overview

Problem

Existing audio encoding methods using SBR technique for low bit rates result in audible artifacts, particularly at transients, due to coarse temporal grids leading to pre-echo issues, while fine grids increase bit consumption.

Innovation Solution

Introduce a new SBR frame class (LD_TRAN) where grid boundaries align with frame boundaries, using a transient position indication to define a short grid area around transients, reducing the need for variable frame classes and minimizing bit transmission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of substance

If a coarse temporal grid is used for spectral envelope encoding, then bit consumption is reduced, but audible artifacts and pre-echo occur at transients

Engineering Contradiction:

Improvebit consumptionVSAvoidaudible artifacts

Core Design Contradiction:

Loss of substanceVSObject-affected harmful factors

Solution Approach 1:

The temporal grid is segmented into two types: regular grid areas and transient grid areas. Transient grid areas are identified by detecting transient positions and creating smaller grid segments around them, while regular areas use coarser grid spacing. This segmentation allows fine resolution where needed (at transients) and coarse resolution elsewhere, reducing overall bit consumption while avoiding artifacts.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different grid resolutions are applied to different temporal regions based on local signal characteristics. Regions containing transients receive fine grid resolution to accurately capture transient energy, while regions without transients use coarse grid resolution to minimize bit consumption. This local adaptation of quality resolves the contradiction between overall bit rate reduction and local artifact prevention.

Inventive Principle:

Principle #3Local quality

2Object-affected harmful factors

If a fine temporal grid is used for spectral envelope encoding, then audible artifacts are reduced, but bit consumption increases

Engineering Contradiction:

Improveaudible artifactsVSAvoidbit consumption

Core Design Contradiction:

Object-affected harmful factorsVSLoss of substance

Solution Approach 1:

Instead of applying a fine grid uniformly across the entire signal, the temporal grid is segmented such that fine resolution is applied only to small regions around detected transients, while the majority of the signal uses coarse grid spacing. This segmentation strategy reduces the total number of grid points requiring spectral envelope encoding, thereby reducing bit consumption while maintaining artifact-free transient representation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Fine grid resolution is applied partially rather than excessively. The system applies fine resolution only where absolutely necessary (at transient locations) and uses coarse resolution for the remainder of the signal. This partial application of fine resolution achieves the goal of artifact reduction without the excessive bit consumption that would result from uniform fine gridding.

Inventive Principle:

Principle #16Partial or excessive action

3Object-affected harmful factors

If variable frame classes are used to handle transients, then transient representation is improved, but device complexity and decoding delay increase

Engineering Contradiction:

Improvetransient representationVSAvoidframe class complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

Instead of varying the frame structure to accommodate transients (which increases complexity), the invention inverts the approach by keeping frame boundaries fixed and varying the grid boundaries within frames. The transient grid areas are defined by offsetting grid boundaries from frame boundaries, allowing flexible transient handling without requiring multiple frame types or increasing decoder complexity.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUSRE50711E1Encoding an information signal

Publication Date: 2025.12.23 FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV

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.