Audio Frame Decoding with LPC Smoothing for Click-Free Transitions
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Solution Overview
Problem
Existing audio signal processing methods using long-term prediction filters often introduce discontinuities between filtered frames, leading to artifacts like 'clicks' due to mismatched filter parameters, and prior solutions can cause additional distortion, especially in harmonic signals with fast-changing pitch.
Innovation Solution
The method employs linear predictive filtering to remove discontinuities by modifying the beginning portion of the filtered current frame using initial states from the past frame, avoiding the use of past frame filter parameters and utilizing Levinson-Durbin algorithm for LPC filter estimation to mask spectral shape and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If long-term prediction filter is used to attenuate harmonics in audio signal, then harmonic suppression is improved, but discontinuities are introduced between filtered frames
Solution Approach 1:
An overlap region is introduced as an intermediary between consecutive filtered frames. This overlap region contains both the end portion of the previous frame and the beginning portion of the current frame, allowing smooth transition and eliminating discontinuities while maintaining harmonic suppression benefits
Solution Approach 2:
The overlap region is prepared in advance by including it in both the previous and current frame processing. This preliminary action ensures that when frames are concatenated, the transition is already smoothed out, preventing discontinuities before they occur
2Object-generated harmful factors
If overlap-add operation is performed to remove discontinuities, then discontinuity removal is improved, but additional distortion is introduced in harmonic signals with fast-changing pitch
Solution Approach 1:
Different processing approaches are applied to different regions of the audio signal. The overlap region receives special handling with linear predictive coding to match spectral characteristics, while the rest of the frames are processed normally. This localized approach removes discontinuities without introducing distortion in regions where it matters most
3Device complexity
If filter parameters from past frame are used for current frame, then processing simplicity is improved, but spectral shape mismatch causes distortion
Solution Approach 1:
Filter parameters are dynamically changed for the overlap region based on the spectral characteristics of the current frame, rather than using fixed parameters from the past frame. This allows the filter to adapt to spectral shape changes, eliminating mismatch distortion while maintaining processing efficiency
Data Source
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AI summary
A method is described that processes an audio signal (100). A discontinuity between a filtered past frame and a filtered current frame of the audio signal is removed using linear predictive filtering (102, 110, 112).