Audio Upmix Distortion Limiter for Bitstream Control

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Solution Overview

Problem

Existing audio processing systems face challenges in providing high-quality upmix signal representations due to audible distortions caused by inappropriate rendering parameter settings, particularly in multi-channel audio applications where bitrate constraints and computational complexity are significant.

Innovation Solution

An apparatus and method that incorporate a distortion limiter to adjust upmix parameters using a distortion control scheme, leveraging distortion limitation control parameters from the bitstream representation to mitigate audible distortions. This involves evaluating dynamic update flags and acquiring distortion limitation control parameters to adjust the distortion control scheme accordingly, ensuring improved audio quality by controlling rendering parameters effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If parametric techniques are used for bitrate-efficient transmission of multi-channel audio, then bitrate requirements are reduced, but audible distortions occur due to inappropriate rendering parameter settings

Engineering Contradiction:

ImprovebitrateVSAvoidaudible distortions

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

The encoder performs preliminary analysis of the downmix signal to determine optimal distortion limitation control parameters before encoding. These parameters are calculated in advance and embedded in the bitstream, allowing the decoder to apply pre-computed distortion limits without real-time computational overhead, thus preventing audible distortions while maintaining bitrate efficiency

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements a feedback mechanism where distortion limitation control parameters are adjusted based on the actual audio content characteristics. The encoder analyzes the downmix signal properties and provides feedback information in the bitstream that guides the decoder's distortion control, creating a closed-loop system that adapts to content-specific requirements and minimizes audible distortions

Inventive Principle:

Principle #23Feedback

2Object-affected harmful factors

If distortion control schemes are applied to reduce audible distortions, then audio quality is improved, but computational complexity increases

Engineering Contradiction:

Improveaudible distortionsVSAvoidcomputational complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

Complex distortion control calculations are performed in advance by the encoder during the encoding phase. The resulting distortion limitation control parameters are stored and transmitted in the bitstream, shifting the computational burden from the decoder to the encoder. This allows the decoder to apply simple look-up or interpolation operations based on the pre-computed parameters, significantly reducing real-time computational complexity

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses the downmix signal itself as the source for determining distortion limitation parameters, eliminating the need for separate analysis signals or additional processing channels. The distortion control mechanism serves itself by deriving all necessary control information from the existing downmix signal characteristics, reducing overall system complexity

Inventive Principle:

Principle #25Self-service

3Object-affected harmful factors

If dynamic update flags are evaluated to acquire distortion limitation control parameters, then audio quality is enhanced, but processing time increases

Engineering Contradiction:

Improveaudible distortionsVSAvoidprocessing time

Core Design Contradiction:

Object-affected harmful factorsVSLoss of time

Solution Approach 1:

The system uses periodic update mechanisms where distortion limitation control parameters are updated at specific intervals rather than continuously. The dynamic update flag indicates when parameter updates occur, allowing the decoder to process audio frames with minimal overhead most of the time and only perform parameter acquisition and adjustment when necessary, thus reducing average processing time while maintaining audio quality

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

Instead of evaluating distortion limitation control parameters for every audio frame, the system applies partial updates only when the dynamic update flag indicates changes are necessary. This selective processing approach performs fewer operations than a full continuous update would require, reducing processing time while still maintaining adequate distortion control for quality enhancement

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS9060236B2Apparatus for providing an upmix signal representation on the basis of a downmix signal representation, apparatus for providing a bitstream representing a multi-channel audio signal, methods, computer program and bitstream using a distortion control signaling

Publication Date: 2015.06.16 DOLBY INTERNATIONAL AB

AI summary

An apparatus for providing an upmix signal representation on the basis of a downmix signal representation and an object-related parametric information, which are included in a bitstream representation of an audio content, and in dependence on a rendering information, has a distortion limiter configured to adjust upmix parameters using a distortion control scheme to avoid or limit audible distortions which are caused by an inappropriate choice of rendering parameters. The distortion limiter is configured to obtain a distortion limitation control parameter, which is included in the bitstream representation of the audio content, and to adjust a distortion control scheme in dependence on the distortion limitation control parameter.