Decoder State Re-Phasing After Packet Loss in G.722 Audio
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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 for updating the decoder state to align with an extrapolated audio signal, calculating a time lag between the extrapolated and decoded signals, and resetting the decoder state to conceal packet loss in sub-band predictive coders, specifically designed for the G.722 coder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If prior-art packet loss concealment methods are applied to sub-band predictive coders, then general packet loss concealment can be achieved, but sub-band-specific architectural issues and backward-adaptive ADPCM challenges are not addressed
Solution Approach 1:
The patent applies local quality by designing packet loss concealment methods specifically tailored for sub-band predictive coders. It updates decoder states separately for each sub-band (low-band and high-band) and handles the specific architectural characteristics of sub-band coding, including the interaction between sub-bands and the backward-adaptive nature of ADPCM coders.
Solution Approach 2:
The patent implements dynamics by continuously updating decoder states based on synthesized output audio signals. It dynamically adjusts decoder states to align with extrapolated signals and recalculates time lags between extrapolated and decoded signals to adapt to changing signal conditions during packet loss events.
2Reliability
If decoder state is continuously updated to align with synthesized signals, then audio quality during packet loss is improved, but computational complexity increases
Solution Approach 1:
The patent applies preliminary action by synthesizing the output audio signal associated with the lost frame before updating the decoder state. It generates an extrapolated signal based on the synthesized signal and uses this pre-computed information to guide the decoder state updates, avoiding the need for complex real-time calculations during packet loss.
Solution Approach 2:
The patent implements feedback by calculating the time lag between the extrapolated signal and the decoded audio signal from the first received frame after packet loss. This time lag information is fed back to reset the decoder state, creating a closed-loop system that continuously adapts to maintain signal alignment and audio quality.
Data Source
AI summary
A technique is described herein for updating a state of a decoder configured to decode a series of frames representing an encoded audio signal. In accordance with the technique, an output audio signal associated with a lost frame in the series of frames is synthesized. The decoder state is set to align with the synthesized output audio signal at a frame boundary. 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 a first received frame after the lost frame in the series of frames, wherein the time lag represents a phase difference between the extrapolated signal and the decoded audio signal. The decoder state is then reset based on the time lag.