SBR Frame Class Encoding for Audio Transient and Pre-Echo Control

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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 transient position indications to define short grid areas 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 spectral envelopes, 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 frame is divided into multiple temporal sub-grids, allowing different grid resolutions in different time segments. This enables fine gridding at transient locations and coarse gridding elsewhere, resolving the contradiction between bit consumption and artifact prevention

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The temporal grid structure is made dynamic by adjusting grid boundaries based on detected transient positions. The grid transitions from uniform coarse structure to adaptive structure with refined regions around transients, optimizing both compression efficiency and audio quality

Inventive Principle:

Principle #15Dynamics

2Object-affected harmful factors

If a fine temporal grid is used for encoding spectral envelopes, 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:

Different temporal regions are assigned different grid resolutions based on their characteristics. Fine gridding is applied locally at transient positions where artifacts occur, while coarse gridding is used in steady-state regions, achieving artifact reduction without global bit rate increase

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The temporal resolution parameter of the grid is changed adaptively based on signal characteristics. The grid density is increased only in regions containing transients, dynamically adjusting the encoding precision to match local signal complexity

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

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

Engineering Contradiction:

Improvetransient processing flexibilityVSAvoidframe class management

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

Instead of adapting frame structures to handle transients (complex approach), the patent inverts the approach by adapting transient detection and grid positioning within fixed frame structures. This simplifies the system while maintaining flexibility in transient processing

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUSRE50801E1Encoding an information signal

Publication Date: 2026.02.17 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.