Decoder State Re-Phasing for Packet Loss in Sub-Band ADPCM Audio

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Solution Overview

Problem

Existing packet loss concealment methods for sub-band predictive coders, such as the ITU-T G.722 coder, face challenges due to sub-band-specific architectural issues and backward-adaptive ADPCM predictive coders, which are not addressed by prior-art techniques.

Innovation Solution

A method and system for updating the decoder state to align with a synthesized output audio signal, generating an extrapolated signal based on the synthesized output, and calculating a time lag to reset the decoder state, specifically designed for sub-band predictive coders like G.722, to address packet loss in audio transmission.

Engineering Contradictions & Design Principles

VSEngineering 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 quality degradation

Engineering Contradiction:

Improvepacket loss concealment effectivenessVSAvoidaudio quality degradation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the timing parameter of decoder state updates by introducing a time lag calculation. Instead of updating states immediately at frame boundaries, the system calculates the phase difference between extrapolated and decoded signals and applies a delayed update, transforming the state update timing to match the actual signal phase alignment

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The system implements feedback by calculating the time lag between extrapolated signals and actual decoded signals, then using this lag information to adjust and reset decoder states. This closed-loop approach ensures the decoder remains synchronized with the concealed audio output

Inventive Principle:

Principle #23Feedback

2Ease of operation

If decoder states are updated immediately at frame boundaries, then processing is simplified, but phase misalignment occurs between extrapolated and decoded signals

Engineering Contradiction:

Improvedecoder state update simplicityVSAvoidsignal phase alignment

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The system performs preliminary calculation of the time lag between extrapolated and decoded signals before updating decoder states. By determining the phase difference in advance and using it to guide the state update timing, the system ensures accurate phase alignment is achieved before the actual update occurs

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP2054879B1Re-phasing of decoder states after packet loss

Publication Date: 2010.01.20 BROADCOM INC

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AI summary

A technique is described for updating a state of a decoder. In accordance with the technique, a decoder state is aligned with a synthesized output audio signal at a frame boundary. An extrapolated signal is generated from 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.