Audio Encoder Bandwidth Control to Avoid Spectral Holes
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Solution Overview
Problem
Audio codecs face issues with perceptual degradation due to zero-quantized spectral lines, leading to artificial noise generation in bandlimited signals, and incorrect bandwidth detection results in audible artefacts like spectral holes.
Innovation Solution
An encoder and decoder system with a bandwidth detector and controller that selectively adjusts the bandwidth for specific tools, allowing only active frequency regions to be processed, thereby avoiding spectral holes and reducing artefacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If bandwidth detection is used to control coding tools, then audio quality is improved by avoiding artificial noise in inactive bands, but reliability deteriorates due to incorrect bandwidth detection causing spectral holes
Solution Approach 1:
The frequency spectrum is divided into multiple scale factor bands, and coding tools are selectively applied to specific bands based on detected signal presence. This segmentation allows the system to process only active frequency regions, avoiding artificial noise in inactive bands while maintaining reliability through localized control.
Solution Approach 2:
The system dynamically adjusts the bandwidth and activation of coding tools based on real-time bandwidth detection results. The controller modifies which coding tools are active in which frequency bands, creating a dynamic adaptation to signal characteristics that resolves the contradiction between quality improvement and reliability.
2Manufacturing precision
If coding tools operate on full bandwidth, then audio quality is maintained across all frequency regions, but harmful factors increase due to artificial noise generation in inactive frequency bands
Solution Approach 1:
Different coding tool configurations are applied to different frequency bands based on local signal characteristics. The system identifies active and inactive bands and applies appropriate coding strategies locally, preventing artificial noise generation in inactive bands while maintaining quality in active bands.
Solution Approach 2:
The system applies coding tools selectively only to the necessary frequency bands rather than uniformly across the full bandwidth. By limiting the action of coding tools to only those bands containing signal content, the system avoids generating artificial noise in inactive bands while maintaining adequate audio quality.
3Object-generated harmful factors
If bandwidth detection is made more sensitive to detect active signal, then harmful factors are reduced by avoiding processing of inactive bands, but measurement precision deteriorates due to false detection of signal fade-out as low bandwidth
Solution Approach 1:
The system uses feedback from bandwidth detection to control the activation of coding tools, and incorporates additional signal characteristics analysis to verify detection results. This feedback mechanism helps distinguish between actual bandwidth limitations and temporary signal fade-out, improving measurement precision while reducing spectral holes.
Solution Approach 2:
The system performs preliminary analysis of signal characteristics before activating coding tools, using multiple detection criteria to confirm the presence of signal content. This preliminary action prevents false detection of low bandwidth conditions and avoids creating spectral holes due to premature tool deactivation.
Data Source
AI summary
There are disclosed apparatus and methods for encoding and/or decoding information signals (e.g., audio signals). An encoder apparatus includes a plurality of frequency domain (FD) encoder tools for encoding an information signal, and an encoder bandwidth detector and controller configured to select a bandwidth for at least a subgroup of the FD encoder tools. The subgroup includes less FD encoder tools than the plurality of FD encoder tools. The selection is based on information signal characteristics, so that one of the FD encoder tools of the subgroup has a different bandwidth with respect to at least one of the FD encoder tools which are not in the subgroup.