Decoded Audio Time-Warping for Packet Loss Transition Smoothing
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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, particularly due to structural issues and challenges posed by Adaptive Differential Pulse Code Modulation (ADPCM) with sample-by-sample backward adaptation, which are not addressed by prior-art techniques.
Innovation Solution
A method and system that transition between lost and received frames by synthesizing an output audio signal, generating an extrapolated signal, calculating a time lag between the extrapolated and decoded signals, and time-warping the decoded signal to align with the extrapolated signal, effectively addressing sub-band-specific architectural issues and backward-adaptive ADPCM challenges.
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 structural issues and backward-adaptive ADPCM challenges cause audio quality degradation
Solution Approach 1:
The patent divides the audio signal processing into sub-bands, where each sub-band is processed independently through separate ADPCM predictive coders. This segmentation allows the system to handle packet loss in individual sub-bands without affecting others, addressing the sub-band-specific structural issues while maintaining overall audio quality.
Solution Approach 2:
The patent modifies the quantizer step size and predictor coefficients dynamically based on signal characteristics and packet loss conditions. By changing these parameters adaptively, the system overcomes the challenges of backward-adaptive ADPCM and maintains audio quality during packet loss concealment.
2Productivity
If backward-adaptive ADPCM is used in sub-band predictive coders, then coding efficiency is improved, but packet loss causes significant audio quality degradation due to unaddressed adaptation challenges
Solution Approach 1:
The patent performs preliminary estimation of quantizer step size and predictor coefficients using forward adaptation before packet loss occurs. This preliminary action allows the system to maintain coding efficiency while preparing for potential packet loss, enabling smoother transition to concealment modes without significant audio quality degradation.
Solution Approach 2:
The patent implements feedback mechanisms where the decoder monitors signal characteristics and adjusts adaptation parameters based on detected packet loss conditions. This feedback loop allows the system to maintain both coding efficiency and audio quality by dynamically switching between normal operation and concealment modes.
3Reliability
If audio waveform extrapolation techniques are applied to sub-band predictive coders, then packet loss concealment is achieved, but sub-band-specific architectural issues cause transition artifacts
Solution Approach 1:
The patent merges the extrapolated waveform from packet loss concealment with the decoded audio signal from subsequent frames using overlap-add techniques. This merging approach smooths the transition between concealed and received frames, eliminating discontinuities and reducing transition artifacts while maintaining packet loss concealment effectiveness.
Solution Approach 2:
The patent dynamically adjusts the mixing ratio between extrapolated and decoded signals based on the duration of packet loss and signal characteristics. This dynamic adjustment allows the system to optimize the transition behavior, reducing artifacts during brief losses while maintaining concealment effectiveness during extended packet loss.
Data Source
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AI summary
A technique is described for use in a decoder to transition between a lost frame and one or more received frames following the lost frame in a series of frames. In accordance with the technique, an extrapolated signal is generated based on a 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.