Audio Frame Discontinuity Removal Using Linear Predictive Filtering
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Solution Overview
Problem
Conventional audio signal processing methods using long-term prediction filters introduce discontinuities between consecutive frames, leading to unwanted artifacts like clicks, especially when past and current frame filter parameters mismatch.
Innovation Solution
Employ a linear predictive filter (LPC) to remove discontinuities by modifying the beginning portion of the current frame using initial states based on the last part of the past frame, avoiding the use of past frame filter parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a long-term prediction filter is used to attenuate harmonics in audio signal frames, then the harmonic attenuation effect is improved, but discontinuities are introduced between consecutive frames when filter parameters change
Solution Approach 1:
The patent applies preliminary action by pre-filtering the beginning portion of the current frame using the past frame's filter parameters before switching to current frame parameters. This preparatory filtering with previous parameters ensures a smooth transition and prevents discontinuities that would otherwise occur when parameters change abruptly.
Solution Approach 2:
The patent implements dynamics by dynamically switching filter parameters between past and current frame values during the transition period. The filter parameters are not static but evolve over time within the beginning portion of the current frame, transitioning from past frame parameters to current frame parameters to maintain continuity.
2Object-generated harmful factors
If overlap-add or cross-fade operation is performed on the beginning portion of the current frame filtered with past frame parameters, then discontinuities are reduced, but additional distortion may be introduced when pitch lag changes rapidly
Solution Approach 1:
The patent applies partial action by filtering only the beginning portion of the current frame with past frame parameters, rather than the entire frame. This limited application of past parameters reduces discontinuities at the frame boundary while minimizing the duration of potential distortion, allowing the signal to quickly transition to current frame parameters.
Solution Approach 2:
The patent implements local quality by applying different filter parameter sets to different portions of the current frame. The beginning portion uses past frame parameters for smooth transition, while the remaining portion uses current frame parameters for accurate harmonic attenuation, optimizing both continuity and signal fidelity locally.
Data Source
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AI summary
A method for processing an audio signal (100) includes receiving an encoded audio signal and generating a decoded audio signal by processing consecutive audio frames of the audio signal to avoid discontinuities. Processing consecutive audio frames of the audio signal to avoid discontinuities includes using linear predictive filtering for removing (S102, S104, S300-S308, S400-S402) a discontinuity (106a, 106b) between a filtered past frame and a filtered current frame of the audio signal. The method includes filtering the current frame of the audio signal and removing the discontinuity by modifying a beginning portion of the filtered current frame by a signal obtained by linear predictive filtering a predefined signal with initial states of the linear predictive filter defined on the basis of a last part of the unfiltered past frame filtered using the set of filter parameters for filtering the current frame.