LC3 Decoder Concealment for Partial and Full Frame Loss
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Solution Overview
Problem
Existing audio codecs face challenges in effectively handling frame loss concealment, particularly in transform-based audio codecs, where missing spectral lines can lead to artefacts, and existing methods like muting, repetition, and noise substitution may not adequately preserve tonality or spectral shape during error concealment.
Innovation Solution
A decoder and decoding method that incorporates an error concealment mode for spectral lines above a threshold frequency, with error concealment techniques varying based on whether the previous frame's signal component is tonal or harmonic, and employs adaptive attenuation and sign manipulation to preserve tonality and spectral shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error concealment is applied to all spectral lines, then audio quality is improved, but computational complexity increases
Solution Approach 1:
The patent applies error concealment selectively to different spectral lines based on their frequency characteristics. Specifically, different concealment strategies are used for low-frequency spectral lines (which carry tonal information) versus high-frequency spectral lines, rather than applying a uniform approach to all spectral lines. This localized differentiation improves audio quality where needed while reducing unnecessary computational overhead.
Solution Approach 2:
The spectrum is divided into different frequency regions with distinct error concealment approaches. The patent segments spectral lines into at least two groups: those requiring tone preservation (typically lower frequencies) and those where simpler concealment suffices (higher frequencies). This segmentation allows the system to manage computational complexity by applying complex concealment only where necessary.
2Reliability
If conventional error concealment techniques are used, then missing spectral lines are replaced, but tonality and spectral shape are not adequately preserved
Solution Approach 1:
The patent modifies the parameters of the error concealment process based on the characteristics of the missing spectral lines and surrounding spectral content. Specifically, it adjusts attenuation factors, interpolation methods, and tone preservation parameters dynamically. When tonal components are detected in adjacent spectral lines, the system changes parameters to preserve that tonality, such as using different attenuation rates or selecting specific reconstruction methods that maintain spectral shape.
Solution Approach 2:
The error concealment approach is made dynamic rather than static. The system continuously analyzes the spectral content and adapts the concealment strategy in real-time based on detected tonal characteristics, energy distribution, and spectral shape. This dynamic adaptation allows the system to preserve tonality when present while using simpler methods when appropriate, thereby improving spectral accuracy without rigid constraints.
Data Source
AI summary
FIG. 1 illustrates a decoder for decoding a current frame to reconstruct an audio signal according to an embodiment. The audio signal is encoded within the current frame. The current frame includes a current bitstream payload. The current bitstream payload includes a plurality of payload bits. The plurality of payload bits encodes a plurality of spectral lines of a spectrum of the audio signal. Each of the payload bits exhibits a position within the current bitstream payload. The decoder includes a decoding module and an output interface. The decoding module is configured to reconstruct the audio signal. The output interface is configured to output the audio signal.