Audio Encoder Variable Warping Filter
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Solution Overview
Problem
Existing audio coding technologies fail to efficiently encode both general audio and speech signals at low bitrates, as general audio coders are not optimized for speech signals and LPC-based speech coders are not effective for music signals due to their inability to adapt to masking threshold curves.
Innovation Solution
An audio encoding system with a pre-filter having a variable warping characteristic, controlled by a time-varying signal, allows for seamless integration of different coding algorithms, using a first algorithm for specific signal patterns and a second algorithm for general audio, with the pre-filter or post-filter adjusting warping to match the BARK or ERB frequency scale for optimal noise shaping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If general audio coding algorithms are used, then general audio quality is improved, but speech coding performance deteriorates at low bitrates
Solution Approach 1:
The pre-filter uses a time-varying warping factor that dynamically adapts to the input signal characteristics. The warping factor is adjusted based on whether the signal is speech or music, allowing the same filter structure to optimize performance for different signal types without requiring separate dedicated coders
Solution Approach 2:
The warping factor parameter is changed according to the signal type detected. For speech signals, a smaller warping factor is applied to preserve spectral envelope accuracy, while for music signals, a larger warping factor is used to achieve better noise shaping according to the masking threshold curve
2Manufacturing precision
If LPC-based speech coding is used, then speech coding performance is improved, but general audio coding performance deteriorates
Solution Approach 1:
The pre-filter with variable warping characteristic serves multiple functions: it acts as an LPC analysis filter for speech coding when the warping factor is small, and as a perceptual noise shaping filter for music coding when the warping factor is large. This single structure replaces the need for separate dedicated speech and music coders
Solution Approach 2:
The filter dynamically switches between speech-optimized and music-optimized configurations by adjusting the warping factor based on signal analysis, allowing the same hardware/software structure to achieve near-specialized-coder performance for both speech and music
3Ease of manufacture
If a fixed warping factor is used, then filter design simplicity is improved, but coding performance for different signal types deteriorates
Solution Approach 1:
Rather than designing different fixed filters for speech and music, the system uses a single filter structure with a dynamically adjustable warping factor. This maintains implementation simplicity while achieving signal-type-specific optimization through runtime parameter adjustment
Data Source
AI summary
An audio encoder, an audio decoder or an audio processor includes a filter for generating a filtered audio signal, the filter having a variable warping characteristic, the characteristic being controllable in response to a time-varying control signal, the control signal indicating a small or no warping characteristic or a comparatively high warping characteristic. Furthermore, a controller is connected for providing the time-varying control signal, which depends on the audio signal. The filtered audio signal can be introduced to an encoding processor having different encoding algorithms, one of which is a coding algorithm adapted to a specific signal pattern. Alternatively, the filter is a post-filter receiving a decoded audio signal.