Switched Audio Decoder Fade-Out Using Common Comfort Noise Tracing
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Solution Overview
Problem
Current audio signal encoding and decoding systems face challenges in effectively managing signal fade-out during error concealment in switched audio coding systems, particularly in maintaining a pleasant noise characteristic and avoiding computational overhead during burst packet losses.
Innovation Solution
An apparatus and method for improved signal fade-out in switched audio coding systems, which involves tracing and applying a common comfort noise level in the excitation domain, ensuring the fade-out to a comfort noise-like signal during burst packet losses, and using a correction factor to adjust the LPC synthesis gain, thereby maintaining a pleasant noise characteristic and reducing computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If independent noise level tracing modules are used for each core coder, then noise level tracking accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges the noise level tracing functionality into a single common module that serves multiple core coders (ACELP and TCX), eliminating the need for separate independent tracing modules for each coder. This shared module traces the comfort noise level once and makes it available to both coders, thereby reducing device complexity while maintaining accurate noise level tracking.
Solution Approach 2:
The common noise level tracing module is designed to be universal and multi-functional, serving both ACELP and TCX core coders with a single implementation. This module can trace comfort noise levels for different coding modes and switch between them, providing multi-coder support without requiring separate specialized modules for each coder type.
2Adaptability or versatility
If separate comfort noise levels are maintained for different core coders, then coder-specific noise characteristics are preserved, but consistency across coders deteriorates
Solution Approach 1:
The system dynamically switches between ACELP and TCX core coders based on signal conditions, and the common noise level tracing module adapts to provide appropriate comfort noise levels for the active coder. The module can adjust its tracing behavior and output levels dynamically to match the requirements of different coding modes while maintaining a single consistent reference level.
3Ease of manufacture
If fade-out is applied in the time domain, then implementation simplicity is improved, but aliasing issues occur
Solution Approach 1:
The patent replaces time-domain fade-out processing with frequency-domain processing. Instead of applying fade-out directly in the time domain where aliasing occurs, the system transforms the signal to the frequency domain, applies the fade-out attenuation to spectral coefficients, and then transforms back to time domain. This substitution of the processing domain eliminates aliasing issues while maintaining implementation feasibility through standard transform operations.
Data Source
AI summary
An apparatus for decoding an audio signal includes a receiving interface, wherein the receiving interface is configured to receive a first frame and a second frame. Moreover, the apparatus includes a noise level tracing unit for determining noise level information being represented in a tracing domain. Furthermore, the apparatus includes a first reconstruction unit for reconstructing a third audio signal portion of the audio signal depending on the noise level information and a second reconstruction unit for reconstructing a fourth audio signal portion depending on noise level information being represented in the second reconstruction domain.