TCX LTP Error Concealment for Spectral Shape and Comfort Noise
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Solution Overview
Problem
Current audio signal encoding and decoding technologies face challenges in effectively managing signal fade-out during error concealment in switched audio coding systems, particularly in maintaining spectral shape and background noise levels during packet loss.
Innovation Solution
The proposed solution involves a method for decoding audio signals that uses a delay buffer and sample processor to select and process audio samples based on pitch lag information, fading the TCX LTP gain to zero and decoupling the TCX LTP feedback loop to preserve spectral shape and transition to a comfort noise level during error concealment, while tracing noise levels using a common comfort noise approach across different coding domains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If TCX LTP feedback loop is maintained during error concealment, then spectral shape is preserved, but unwanted tonal components are introduced
Solution Approach 1:
The patent segments the LTP processing into two distinct paths: during normal operation, the full LTP feedback loop operates to maintain spectral shape; during error concealment, the LTP feedback is decoupled and replaced with comfort noise generation. This segmentation allows the system to preserve beneficial spectral characteristics while eliminating harmful tonal components in the error concealment mode.
Solution Approach 2:
Instead of maintaining the LTP feedback loop during error concealment as would be conventional, the patent inverts the approach by decoupling the LTP feedback and replacing it with comfort noise. This inversion prevents the generation of unwanted tonal components while still providing continuous audio output during packet loss.
2Speed
If fade-out speed is increased during error concealment, then transition to comfort noise is faster, but signal quality degradation is more pronounced
Solution Approach 1:
The patent implements dynamic fade-out control where the attenuation factor is adaptively adjusted based on the number of consecutive lost frames. For short-term losses, a slower fade-out is applied to maintain signal quality; for long-term losses, a faster fade-out transitions more quickly to comfort noise. This dynamic adjustment resolves the contradiction between fade-out speed and signal quality preservation.
3Stability of the object's composition
If common comfort noise tracing is implemented across different coding domains, then consistent comfort noise experience is achieved, but computational complexity increases
Solution Approach 1:
The patent implements a universal comfort noise tracing mechanism that operates across both ACELP and TCX coding domains using a common set of parameters and algorithms. This multi-functional approach ensures consistent comfort noise generation regardless of the active coding mode, while avoiding the need for separate tracing mechanisms for each domain, thereby limiting the increase in computational complexity.
Data Source
AI summary
An apparatus for decoding an encoded audio signal to obtain a reconstructed audio signal is provided. The apparatus includes a receiving interface, a delay buffer and a sample processor for processing the selected audio signal samples to obtain reconstructed audio signal samples of the reconstructed audio signal. The sample selector is configured to select, if a current frame is received by the receiving interface and if the current frame being received by the receiving interface is not corrupted, the plurality of selected audio signal samples from the audio signal samples being stored in the delay buffer depending on a pitch lag information being included by the current frame.