SBR Temporal Grid Encoding for Transient Pre-Echo Reduction

Solution Overview

Problem

Existing audio encoding methods using SBR technique for low bit rates result in audible artefacts, 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 artefacts and pre-echo occur at transients

Engineering Contradiction:

Improvebit consumptionVSAvoidaudible artefacts and pre-echo

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 shorter grid segments around them, while regular areas use the standard coarse grid. This segmentation allows fine resolution only where needed (at transients) while maintaining coarse resolution elsewhere, thus reducing overall bit consumption while avoiding pre-echo artefacts.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different temporal resolutions are applied locally depending on the signal characteristics. In transient grid areas, a fine temporal grid is used to accurately capture transient events, while in regular grid areas, a coarse temporal grid is used to minimize bit consumption. This local adaptation of grid fineness resolves the contradiction by applying fine resolution only where it is necessary to avoid artefacts.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If a fine temporal grid is used for spectral envelope encoding, then transient representation is improved, but bit consumption increases

Engineering Contradiction:

Improvetransient representation accuracyVSAvoidbit consumption

Core Design Contradiction:

Measurement precisionVSLoss of substance

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 shorter grid segments around them, while regular areas use the standard coarse grid. This segmentation allows fine resolution only where needed (at transients) while maintaining coarse resolution elsewhere, thus reducing overall bit consumption while avoiding pre-echo artefacts.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different temporal resolutions are applied locally depending on the signal characteristics. In transient grid areas, a fine temporal grid is used to accurately capture transient events, while in regular grid areas, a coarse temporal grid is used to minimize bit consumption. This local adaptation of grid fineness resolves the contradiction by applying fine resolution only where it is necessary to avoid artefacts.

Inventive Principle:

Principle #3Local quality

3Measurement precision

If variable frame classes are used to handle transients, then transient processing is improved, but decoding delay increases

Engineering Contradiction:

Improvetransient processing accuracyVSAvoiddecoding delay

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The grid structure is made dynamic by allowing transient grid areas to have different boundaries than regular grid areas. The transient grid areas are defined relative to the detected transient position, allowing the grid to adapt its structure dynamically based on signal content. This dynamic approach improves transient processing while maintaining compatibility with the standard frame structure, thus reducing decoding delay.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The temporal resolution parameter is changed locally around transient positions. By detecting transient positions and creating shorter grid segments around them, the effective temporal resolution is increased at critical moments without changing the overall frame structure or requiring variable frame classes. This parameter adaptation resolves the contradiction by improving transient accuracy without introducing additional decoding delay.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUSRE50695E1Encoding an information signal

Publication Date: 2025.12.09 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.