Multi-Channel Audio Envelope Shaping for Transient Spatial Accuracy
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Solution Overview
Problem
Current multi-channel audio coding technologies face challenges in accurately reproducing the spatial distribution of signals with high temporal granularity, particularly for transient signals like applause, leading to poor transient reproduction and unnatural sound perception due to inadequate temporal and spectral envelope matching.
Innovation Solution
The proposed solution involves a decoder and encoder system that uses a waveform parameter representation with intermediate time resolution to shape upmixed channels, allowing for finer temporal control of the signal envelope without increasing the bit rate significantly, by deriving a low-resolution representation of the channel and calculating waveform parameters with a time resolution higher than the frame repetition rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If frame-based parametric coding is used to reduce bit rate, then data transmission efficiency is improved, but temporal resolution is reduced leading to poor transient signal reproduction
Solution Approach 1:
The patent segments the temporal representation into multiple resolution levels: frame-based parametric data for overall structure and slot-based waveform parameters for fine temporal details. This hierarchical segmentation allows simultaneous achievement of low bit rate (through frame-based compression) and high temporal accuracy (through slot-based refinement), directly resolving the contradiction between bit rate efficiency and transient signal reproduction quality.
Solution Approach 2:
The patent introduces an intermediate time resolution dimension between frame level and sample level. By creating slot-based waveform parameter representations at this intermediate resolution, the system adds a temporal granularity dimension that enables accurate transient reproduction without requiring full sample-rate transmission, thus resolving the bit rate versus temporal accuracy contradiction.
2Manufacturing precision
If high time resolution waveform parameters are transmitted to improve transient reproduction, then spatial audio quality is improved, but bit rate increases significantly
Solution Approach 1:
The patent applies local quality by providing high temporal resolution waveform parameters only where needed (in slots containing transient events) rather than uniformly across all time. The system selectively refines temporal representation based on local signal characteristics, achieving high transient reproduction quality only when necessary and reducing overall bit rate by using coarser frame-based representation elsewhere.
Solution Approach 2:
The patent implements partial action by transmitting waveform parameters at high time resolution only for specific slots rather than continuously. The system applies fine temporal resolution selectively to slots that require it for accurate transient reproduction, while using lower resolution frame-based parameters for other slots, thus achieving necessary audio quality without excessive bit rate consumption.
3Adaptability or versatility
If decorrelated signals are mixed to create wide sound image, then spatial distribution is improved, but temporal envelope matching deteriorates causing unnatural transient perception
Solution Approach 1:
The patent applies preliminary action by pre-shaping the temporal envelope of decorrelated signals using slot-based waveform parameters before mixing them with direct signals. By preparing the temporal characteristics of diffuse signals in advance at slot-level resolution, the system ensures proper temporal envelope matching occurs prior to spatial mixing, preventing unnatural transient perception while maintaining wide sound image.
Solution Approach 2:
The patent introduces slot-based waveform parameters as an intermediary representation between frame-based parametric data and time-domain audio signals. This intermediate representation serves as a mediator that enables precise temporal envelope control of decorrelated signals during the mixing process, allowing simultaneous achievement of good spatial distribution and temporal envelope matching.
Data Source
AI summary
A selected channel of a multi-channel signal which is represented by frames composed from sampling values having a high time resolution can be encoded with higher quality when a wave form parameter representation representing a wave form of an intermediate resolution representation of the selected channel is derived, the wave form parameter representation including a sequence of intermediate wave form parameters having a time resolution lower than the high time resolution of the sampling values and higher than a time resolution defined by a frame repetition rate. The wave form parameter representation with the intermediate resolution can be used to shape a reconstructed channel to retrieve a channel having a signal envelope close to that one of the selected original channel. The time scale on which the shaping is performed is shorter than the time scale of a framewise processing, thus enhancing the quality of the reconstructed channel. On the other hand, the shaping time scale is larger than the time scale of the sampling values, significantly reducing the amount of data needed by the wave form parameter representation.