MCLT Audio Coder Reducing Warbling Artifacts
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Solution Overview
Problem
Conventional audio compression systems using modulated lapped transforms (MLT) suffer from shift-invariant representation issues, leading to modulation artifacts like 'warbling' in reconstructed audio signals, while MCLT-based coders reduce these artifacts but incur significant rate overhead due to oversampling.
Innovation Solution
An Overcomplete Audio Coder employs MCLT-based predictive coding, transforming coefficients to polar coordinates, using unrestricted polar quantization and predicting magnitude and phase coefficients to reduce bit rate overhead, achieving efficient encoding with reduced warbling artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If MCLT is used to reduce modulation artifacts, then audio quality is improved, but coding rate increases due to oversampling
Solution Approach 1:
The patent changes the coordinate system parameter from rectangular to polar coordinates, transforming the representation of MCLT coefficients. This parameter change enables more efficient quantization strategies that reduce the coding rate while preserving audio quality and reducing modulation artifacts.
Solution Approach 2:
The patent segments the MCLT coefficients into magnitude and phase components in polar coordinates, allowing independent quantization and prediction processing for each component. This segmentation enables more efficient coding by treating different aspects of the signal separately.
2Measurement precision
If MCLT oversampling is used to improve frequency resolution, then measurement precision is improved, but loss of information increases due to redundant coefficients
Solution Approach 1:
The patent extracts and removes redundant information from the overcomplete MCLT representation through prediction techniques. By predicting magnitude and phase coefficients from previous frames and encoding only the residuals, the system eliminates redundant coefficient transmission while preserving the high frequency resolution benefit of MCLT oversampling.
3Object-affected harmful factors
If conventional MCLT coding is used to reduce warbling artifacts, then audio quality is improved, but device complexity increases due to iterative algorithms
Solution Approach 1:
The patent replaces complex iterative sparsity reduction algorithms with simpler, non-iterative prediction and quantization methods. The solution uses computationally efficient prediction of magnitude and phase coefficients that achieves similar artifact reduction without the computational burden of iterative procedures.
Data Source
AI summary
An “Overcomplete Audio Coder” provides various techniques for overcomplete encoding audio signals using an MCLT-based predictive coder. Specifically, the Overcomplete Audio Coder uses unrestricted polar quantization of MCLT magnitude and phase coefficients. Further, quantized magnitude and phase coefficients are predicted based on properties of the audio signal and corresponding MCLT coefficients to reduce the bit rate overhead in encoding the audio signal. This prediction allows the Overcomplete Audio Coder to provide improved continuity of the magnitude of spectral components across encoded signal blocks, thereby reducing warbling artifacts. Coding rates achieved using these prediction techniques are comparable to that of encoding an orthogonal representation of an audio signal, such as with modulated lapped transform (MLT)-based coders. Finally, the Overcomplete Audio Coder provides a true magnitude-phase frequency-domain representation of the audio signal, thus allowing precise auditory models to be applied for improving compression performance, without the need for additional Fourier transforms.