Sub-Band Audio Extrapolation for Lost ADPCM Speech Frames
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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 Adaptive Differential Pulse Code Modulation (ADPCM) predictive coders.
Innovation Solution
A method and system for concealing packet loss in sub-band predictive coders, involving waveform extrapolation techniques tailored for sub-band ADPCM coders, where received frames are decoded to generate full-band audio signals, and synthesized sub-band signals are combined to produce a full-band output signal for lost frames, using a decoder, buffers, synthesizers, and a synthesis filter bank.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If prior-art packet loss concealment methods are applied to sub-band predictive coders, then general audio signal extrapolation can be performed, but sub-band-specific structural issues and backward-adaptive ADPCM challenges are not addressed, resulting in inadequate concealment quality
Solution Approach 1:
The audio signal is divided into multiple sub-bands (e.g., low-band and high-band), and packet loss concealment is performed independently for each sub-band using separate extrapolation processes. This allows the system to address sub-band-specific characteristics and structural issues while maintaining overall audio quality.
Solution Approach 2:
Different concealment strategies and parameters are applied to different sub-bands based on their specific characteristics. The low-band and high-band signals undergo distinct extrapolation processes tailored to their respective frequency ranges and adaptive predictor requirements, improving overall concealment quality.
2Reliability
If waveform extrapolation is performed on full-band audio signals, then packet loss can be concealed, but sub-band-specific structural issues and backward-adaptive quantizer step size challenges remain unaddressed
Solution Approach 1:
The concealment system processes each sub-band separately through dedicated synthesizers and extrapolation modules, then combines the results. This segmented approach maintains audio quality while systematically addressing sub-band-specific structural issues without overwhelming complexity.
Solution Approach 2:
The system performs preliminary extrapolation of sub-band signals using stored historical data before packet loss occurs, and maintains separate state variables for each sub-band's adaptive predictor. This preparation enables rapid response to packet loss while preserving the complex sub-band ADPCM structure.
3Productivity
If sub-band signals are separately decoded and combined, then full-band output can be generated, but the process requires multiple buffers and synthesizers increasing system complexity
Solution Approach 1:
The system employs separate decoders, buffers, and synthesizers for each sub-band, allowing parallel processing and independent optimization of each frequency range. This segmentation enables efficient full-band signal generation despite the increased component count.
Solution Approach 2:
After independent processing of sub-band signals through multiple components, the system merges the low-band and high-band signals to reconstruct the full-band output. This combining operation consolidates the results from multiple complex components into a unified audio signal.
Data Source
AI summary
A technique is described for concealing the effect of a lost frame in a series of frames representing an encoded audio signal in a sub-band predictive coding system. In accordance with the technique, a first synthesized sub-band audio signal is synthesized, wherein synthesizing the first synthesized sub-band audio signal comprises performing waveform extrapolation based on a stored first sub-band decoded audio signal. A second synthesized sub-band audio signal is also synthesized, wherein synthesizing the second synthesized sub-band audio signal comprises performing waveform extrapolation based on the stored second sub-band decoded audio signal. The first synthesized sub-band audio signal and the second synthesized sub-band audio signal are combined to generate a synthesized full-band output audio signal corresponding to a lost frame.