Decoded Audio Time-Warping for Packet Loss Phase Alignment
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Solution Overview
Problem
Existing packet loss concealment methods are inadequate for sub-band predictive coders like the ITU-T G.722 wideband speech coder, as they fail to address sub-band-specific architectural issues and the challenges posed by backward-adaptive ADPCM coders.
Innovation Solution
A method and system that synthesize an output audio signal for a lost frame, generate an extrapolated signal, calculate a time lag between the extrapolated and decoded signals, and time-warp the decoded signal to align with the extrapolated signal, addressing the unique challenges of sub-band predictive coders and backward-adaptive ADPCM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If prior-art packet loss concealment methods are applied to sub-band predictive coders, then packet loss effects can be concealed, but sub-band-specific architectural issues and backward-adaptive ADPCM challenges are not addressed, resulting in degraded audio quality
Solution Approach 1:
The patent applies local quality by adapting the packet loss concealment method specifically for sub-band predictive coders. It processes each sub-band independently with sub-band-specific handling, including separate extrapolation for low-band and high-band signals, and applies time-warping specifically to the decoded audio signal to match the extrapolated signal characteristics. This localized adaptation ensures the PLC method works effectively with the specific architectural constraints of sub-band coders like G.722.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting the time-warping parameter (time lag) based on the correlation between extrapolated and decoded signals. The method calculates the time lag that maximizes signal correlation and applies time-warping with this calculated parameter to align the phases. This dynamic parameter adjustment allows the system to adapt to varying signal conditions and maintain audio quality across different packet loss scenarios.
2Stability of the object's composition
If audio waveform extrapolation is used for packet loss concealment, then smooth transition can be achieved, but phase misalignment between extrapolated and decoded signals causes degradation
Solution Approach 1:
The patent implements feedback by calculating the correlation between the extrapolated signal and the decoded audio signal, then using this correlation information to determine the optimal time lag for time-warping. The method continuously monitors the phase relationship and adjusts the time-warping parameter accordingly to maximize signal correlation. This feedback mechanism ensures that the transition between lost and received frames remains smooth while maintaining precise phase alignment.
Solution Approach 2:
The patent applies dynamics by making the time-warping parameter dynamic rather than fixed. The time lag parameter is calculated adaptively based on the actual signal characteristics and phase relationship between extrapolated and decoded signals. This dynamic adjustment allows the system to respond to varying signal conditions in real-time, ensuring both smooth transitions and accurate phase alignment across different audio content and packet loss patterns.
3Reliability
If time-warping is applied to align extrapolated and decoded signals, then audio quality is maintained, but additional processing complexity is introduced
Solution Approach 1:
The patent applies partial action by implementing time-warping only on the decoded audio signal rather than processing both extrapolated and decoded signals equally. The method calculates the time lag once based on correlation and applies the warping operation selectively to align phases. This partial application of time-warping maintains audio quality while reducing the overall processing complexity compared to more comprehensive signal processing approaches.
Data Source
AI summary
A technique is described for use in a decoder configured to decode a series of frames representing an encoded audio signal. The technique is for transitioning between a lost frame and one or more received frames following the lost frame in the series of frames. In accordance with the technique, an output audio signal associated with the lost frame is synthesized. An extrapolated signal is generated based on the synthesized output audio signal. A time lag is calculated between the extrapolated signal and a decoded audio signal associated with the received frame(s), wherein the time lag represents a phase difference between the extrapolated signal and the decoded audio signal. The decoded audio signal is time-warped based on the time lag, wherein time-warping the decoded audio signal comprises stretching or shrinking the decoded audio signal in the time domain.