Transient-Aware SBR Audio Encoding for Low-Bitrate Signals

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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 encoding the spectral envelope, then bit consumption is reduced, but audible artifacts and pre-echo occur at transients

Engineering Contradiction:

Improvebit consumptionVSAvoidaudible artifacts and pre-echo

Core Design Contradiction:

Loss of substanceVSObject-affected harmful factors

Solution Approach 1:

The temporal grid is segmented into different regions: coarse grid areas for non-transient portions and fine grid areas around detected transients. This allows the encoder to use coarse gridding most of the time (saving bits) while applying fine gridding only where needed (avoiding artifacts), thus resolving the contradiction between bit efficiency and audio quality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different grid resolutions are applied to different temporal regions based on local signal characteristics. The encoder detects transient positions and applies fine temporal gridding locally around these transients, while using coarse gridding in other regions. This local adaptation of grid quality eliminates pre-echo artifacts at transients without increasing overall bit consumption.

Inventive Principle:

Principle #3Local quality

2Object-affected harmful factors

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

Engineering Contradiction:

Improveaudible artifacts and pre-echoVSAvoidbit consumption

Core Design Contradiction:

Object-affected harmful factorsVSLoss of substance

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of applying fine gridding throughout the entire signal (excessive action), the encoder applies fine gridding only partially around detected transient regions. This partial application of fine gridding is sufficient to eliminate pre-echo artifacts while avoiding 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 processing is improved, but device complexity and decoding delays increase

Engineering Contradiction:

Improvetransient processing qualityVSAvoidframe class management complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

Instead of varying the frame structure to accommodate transients (complex approach), the invention inverts the approach by keeping frame boundaries fixed and varying the grid boundaries within frames. A single frame class is used, but the temporal grid is dynamically adjusted within frames based on transient detection, simplifying frame management while still improving transient processing.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

A single frame class structure is designed to handle both transient and non-transient regions universally. The temporal grid within frames can be dynamically configured to accommodate different scenarios (transients at different positions, multiple transients, or no transients), eliminating the need for multiple specialized frame classes and reducing decoding complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUSRE50654E1Encoding an information signal

Publication Date: 2025.11.04 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.