Multi-Channel Audio Envelope Shaping for Dense Transients
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Solution Overview
Problem
Current multi-channel audio coding techniques struggle to accurately preserve the spatial distribution of signals with dense transient events, such as applause, due to limitations in temporal and spectral envelope control, leading to poor reproduction quality and introduction of artefacts like pre-echo and unnatural sound perception.
Innovation Solution
The proposed solution involves guided envelope shaping, where a low-time-resolution waveform parameter representation is used to shape the reconstructed channel, allowing for finer temporal granularity and reduced data requirements, enhancing the spatial distribution and quality of the reconstructed signal without significant increases in control information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If decorrelated signal is generated using all-pass filter (reverberator) to achieve wide sound image, then spatial distribution is improved, but temporal envelope matching deteriorates causing pre-echo artefacts and unnatural transient reproduction
Solution Approach 1:
The patent applies preliminary action by estimating the temporal envelope of the decorrelated signal before mixing it with the downmix signal, and shaping it to match the downmix signal's envelope. This pre-shaping prevents pre-echo artefacts and improves transient reproduction by ensuring the decorrelated signal's envelope is prepared in advance to match the original signal characteristics.
Solution Approach 2:
The patent changes the temporal envelope parameter of the decorrelated signal by estimating its envelope and applying shaping to match the downmix signal's envelope. This parameter modification resolves the contradiction by adjusting the temporal characteristics while maintaining the spatial benefits of decorrelation.
2Manufacturing precision
If temporal envelope shaping is applied to decorrelated signal to match downmix channel, then transient reproduction is improved, but computational complexity increases
Solution Approach 1:
The patent applies self-service by having the decorrelated signal's temporal envelope automatically matched to the downmix signal's envelope through estimation and shaping processes. The system serves itself by deriving the necessary envelope information from the available downmix signal without requiring additional complex external processing or transmitted side information.
Solution Approach 2:
The patent uses copying by estimating the temporal envelope of the decorrelated signal and shaping it to copy the envelope characteristics of the downmix signal. This copying approach allows the decorrelated signal to inherit the temporal envelope properties of the original signal, improving transient reproduction without requiring direct access to the original signal.
3Measurement precision
If high temporal resolution is used for envelope shaping to preserve spatial distribution of dense transients, then audio quality is improved, but data rate increases
Solution Approach 1:
The patent achieves high temporal resolution envelope shaping without increasing data rate by using self-service - the envelope shaping is performed using only the available downmix signal and decorrelated signal, without requiring any additional transmitted side information. The system derives all necessary information from the signals already present in the decoder.
Solution Approach 2:
The patent copies the temporal envelope characteristics from the downmix signal to the decorrelated signal through estimation and shaping, avoiding the need to transmit separate envelope information. This copying mechanism preserves spatial distribution of dense transients while maintaining data rate efficiency.
Data Source
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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.