Audio Signal Encoding with Adaptive Residual Attenuation
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Solution Overview
Problem
Existing audio coding techniques, such as parametric stereo coders, face limitations in achieving proportional increases in audio quality with higher bit rates due to abrupt changes in bit rate and audible switching artifacts when selecting parts of the residual signal for encoding.
Innovation Solution
A device and method that encode a set of input signals by converting them into a dominant signal and a residual signal, selecting and encoding only perceptually relevant parts of the residual signal, attenuating less relevant parts, and suppressing unimportant parts, while controlling the selection based on available transmission rate, and decoding these signals to produce improved output signals with gradual transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If only perceptually relevant parts of the residual signal are encoded while discarding less relevant parts, then bit rate is reduced, but audio quality degrades due to abrupt changes and switching artifacts
Solution Approach 1:
The patent applies parameter changes by using different attenuation factors for the synthetic residual signal based on the available bit rate. When bit rate increases, the attenuation factor decreases, allowing more of the synthetic residual signal to be used. This continuous parameter adjustment resolves the contradiction by smoothly transitioning between different coding modes rather than abruptly switching, thereby maintaining audio quality while adapting to available bit rate.
Solution Approach 2:
The patent introduces dynamics by making the attenuation of the synthetic residual signal adaptive to the available bit rate. Instead of a fixed selection approach, the system dynamically adjusts the contribution of the synthetic residual signal based on current bit rate conditions. This dynamic adaptation allows the system to optimize the trade-off between bit rate and audio quality in real-time, preventing abrupt changes and switching artifacts.
2Quantity of substance
If the residual signal is completely discarded to maximize bit rate reduction, then bit rate is minimized, but audible signal degradation occurs especially at low frequencies
Solution Approach 1:
The patent introduces an intermediary approach by generating a synthetic residual signal that serves as a compromise between completely discarding the residual signal and transmitting it in full. This synthetic signal is created based on the dominant signal and binaural parameters, providing a reasonable approximation of the original residual signal without requiring full transmission. The synthetic residual signal acts as a mediator that reduces bit rate while minimizing audible degradation.
Solution Approach 2:
The patent uses parameter changes by controlling the attenuation factor of the synthetic residual signal based on frequency and bit rate conditions. At low frequencies where phase and time offsets are more critical, the attenuation is reduced to preserve signal quality. This parameter-based control allows the system to adaptively manage the trade-off between bit rate reduction and signal degradation across different frequency ranges.
3Reliability
If more of the residual signal is transmitted to improve audio quality, then audio quality increases, but bit rate increases proportionally
Solution Approach 1:
The patent applies the copying principle by creating a synthetic residual signal that replicates the essential characteristics of the original residual signal without transmitting it in full. Instead of copying and transmitting the entire residual signal, the system generates a synthetic version based on the dominant signal and binaural parameters (IID and ICC). This synthetic copy provides a reasonable approximation that maintains audio quality while significantly reducing the bit rate required compared to transmitting the original residual signal.
Data Source
AI summary
An encoding device (1) and method convert a set of signals (l, r) into a dominant signal (m) containing most signal energy, a residual signal (s) containing a remainder of the signal energy, and signal parameters (IID, ICC) associated with the conversion. The dominant signal (m) and selected parts of the residual signal (s) are encoded. Selecting parts of the residual signal involves a residual signal (s′) passing perceptually relevant parts of the residual signal (s), attenuating perceptually less relevant parts of the residual signal and suppressing least relevant parts of the residual signal. An associated decoding device (2) and method decode the encoded dominant signal and the encoded residual signal so as to produce a decoded dominant signal (m′u) and a decoded residual signal (s′mod) respectively. A synthetic residual signal (s′Syn) is derived from the decoded dominant signal (m′u) and is attenuated so as to produce an attenuated synthetic residual signal (S′Syn,mod). The attenuated synthetic residual signal (Ssyn,mod) and the decoded residual signal (S′mod) are combined to produce a reconstructed residual signal (s′). The decoded dominant signal (m′) and the reconstructed residual signal (s′) are then converted into a set of output signals (l′, r′).