Decoded Audio Time-Warping for Packet Loss Frame 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 structural 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 structural issues and backward-adaptive ADPCM challenges are not addressed, resulting in degraded audio quality
Solution Approach 1:
The patent applies different processing methods to different sub-bands. The full-band signal is extrapolated while individual sub-band signals are processed separately with sub-band-specific parameters, allowing each sub-band to be handled according to its specific characteristics and requirements of backward-adaptive ADPCM coders.
Solution Approach 2:
The audio signal is divided into multiple sub-bands for separate processing. Each sub-band is processed independently through the extrapolation and time-warping operations, allowing the system to address sub-band-specific structural issues while maintaining overall signal coherence.
2Reliability
If audio waveform extrapolation techniques are applied directly to sub-band predictive coders, then packet loss can be concealed, but sub-band-specific structural issues cause misalignment between extrapolated and decoded signals
Solution Approach 1:
The patent introduces time-warping as an intermediary operation between signal extrapolation and decoding. This intermediate step calculates time lags and adjusts the timing of extrapolated signals to match the decoded signals, serving as a mediator that resolves the misalignment caused by sub-band-specific structural issues.
Solution Approach 2:
The system dynamically adjusts time parameters by calculating time lags between extrapolated and decoded signals. This parameter change through time-warping allows the system to compensate for misalignments and maintain precise signal synchronization despite sub-band processing variations.
3Productivity
If backward-adaptive ADPCM predictive coding is used, then coding efficiency is improved, but packet loss concealment becomes more difficult due to sample-by-sample backward adaptation of quantizer step size and predictor coefficients
Solution Approach 1:
The patent performs signal extrapolation and time-warping adjustments before the final decoding stage. By preparing the concealed signals in advance with proper timing alignment, the system simplifies the overall packet loss concealment process while maintaining compatibility with backward-adaptive ADPCM's sample-by-sample adaptation mechanism.
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.