Audio Signal Phase Reconstruction via IPD Coding
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Solution Overview
Problem
Existing signal processing methods, such as those using decorrelators, struggle to precisely reproduce phase or delay differences between channel signals and fail to accurately restore inter-channel phase differences, leading to difficulties in sound image localization and reverberation reconstruction.
Innovation Solution
The proposed method involves an apparatus and method for processing signals by shifting the phase of decoded audio or speech signals based on phase shift flags, utilizing inter-channel phase difference (IPD) coding and mode flags to reconstruct reverberation and enhance sound image localization, while also transmitting and modifying IPD values to improve coding efficiency and compatibility with conventional systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a decorrelator is used to generate a stereo signal from a mono signal, then the signal can be processed with reduced complexity, but the phase or delay difference between channel signals cannot be precisely reproduced
Solution Approach 1:
The patent changes the parameter representation from time-domain decorrelation to frequency-domain phase difference coding. By transforming the signal to frequency domain and directly encoding inter-channel phase difference (IPD) values, the system achieves precise phase reproduction while maintaining computational efficiency through parameter-based representation rather than complex filtering operations
Solution Approach 2:
The patent replaces the mechanical/decorrelator-based approach with a frequency-domain transformation approach. Instead of using decorrelators to indirectly affect phase relationships, the system directly manipulates phase parameters in the frequency domain, substituting a mathematical transformation method for a signal processing mechanism
2Ease of manufacture
If inter-channel level difference value and inter-channel correlation value are used for signal coding, then the coding can be performed with existing methods, but the inter-channel phase difference of the input signal cannot be restored and reflected
Solution Approach 1:
The patent segments the spatial information coding into multiple independent parameters: inter-channel level difference (ILD), inter-channel correlation (ICC), and inter-channel phase difference (IPD). By dividing the spatial coding task into separate parameter streams, the system can selectively encode and transmit IPD information without affecting the existing ILD and ICC coding frameworks, thus preserving phase information while maintaining ease of implementation
Solution Approach 2:
The patent adds a new dimension to spatial audio coding by introducing frequency-domain phase difference parameters. Instead of relying solely on time-domain statistics (correlation and level difference), the system incorporates phase information across frequency bins, creating a multi-dimensional representation that includes magnitude, correlation, and phase aspects of inter-channel relationships
3Measurement precision
If inter-channel phase difference value is transmitted and used, then the sound image localization and reverberation reconstruction are improved, but the compatibility with conventional systems that do not use IPD values is reduced
Solution Approach 1:
The patent implements dynamic adaptability by making the IPD decoding path controllable and switchable. The system can dynamically adjust whether to apply IPD-based phase reconstruction based on system capabilities and input conditions, allowing conventional systems to operate in their existing mode while enhanced systems can utilize the additional phase information for improved sound image localization and reverberation reconstruction
Solution Approach 2:
The patent creates a universal decoding framework that can handle both conventional spatial coding (without IPD) and enhanced spatial coding (with IPD). The apparatus is designed to process spatial information parameters flexibly, supporting multiple input formats and decoding modes, thus maintaining backward compatibility while enabling forward compatibility with systems that utilize inter-channel phase difference values
Data Source
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AI summary
A method of processing a signal is disclosed. The present invention includes receiving (a) a downmix signal being generated from plural-channel signal and (b) spatial information indicating attribute of the plural-channel signal, in order to upmix the downmix signal; obtaining inter-channel phase difference(IPD) coding flag indicating whether IPD value is used to the spatial information from a header of the spatial information; obtaining IPD mode flag indicating whether the IPD is used to frame of the spatial information from the frame based on the IPD coding flag; obtaining the IPD value from a parameter band in the frame based on the IPD mode flag; generating plural-channel signal by applying the IPD value to the downmix signal, wherein the spatial information is divided by header and a plurality of the frame and wherein the IPD value indicates phase difference between two channels of the plural-channel signal and wherein the parameter band is at least one sub-band of frequency domain including the IPD value.