Audio Decoder Frame Smoothing With LPC Discontinuity Removal
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing audio signal processing techniques using long-term prediction filters often introduce discontinuities between filtered frames, leading to artifacts like 'clicks' due to mismatched filter parameters, and conventional methods to remove these discontinuities can result in additional distortion, especially in harmonic audio 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 a signal obtained from linear predictive filtering with initial states based on the last part of the unfiltered past frame, avoiding the use of past frame filter parameters and thus minimizing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If long-term prediction filter is used to attenuate harmonics in audio signal, then the filtering effect is improved, but discontinuities are introduced between filtered frames
Solution Approach 1:
A cross-fade operation is introduced as an intermediary process between consecutive filtered frames. The cross-fade gradually transitions between different filter parameter sets by blending the filtered past frame and filtered current frame over a transition period, thereby eliminating abrupt discontinuities while preserving the harmonic attenuation effect of the long-term prediction filter
Solution Approach 2:
The filter parameters are made dynamic by allowing them to change between frames while applying a cross-fade transition. Instead of using static filter parameters throughout, the system dynamically adjusts parameters (gain g and pitch lag T) from one frame to the next, with the cross-fade smoothing the transition to maintain continuity
2Adaptability or versatility
If filter parameters are changed between past frame and current frame, then the adaptability to different audio segments is improved, but discontinuities and artifacts are introduced
Solution Approach 1:
The cross-fade operation serves as a mediator that smooths the transition between different filter parameter sets. By gradually blending the output of the past frame filter parameters with the current frame filter parameters, the system maintains adaptability to different audio segments while eliminating the harmful discontinuity artifacts that would otherwise result from abrupt parameter changes
Solution Approach 2:
The system intentionally changes filter parameters (gain g and pitch lag T) between frames to adapt to different audio characteristics, but applies a cross-fade transition to manage these parameter changes smoothly. This allows the system to exploit parameter variability for better adaptation while controlling the harmful effects through the transition mechanism
3Stability of the object's composition
If overlap-add or cross-fade operation is applied to remove discontinuities, then the continuity between frames is improved, but the device complexity is increased
Solution Approach 1:
The cross-fade operation is applied only to a portion of the frame boundary region rather than the entire frame. By limiting the cross-fade to a specific transition period at the boundary between frames, the system achieves continuity improvement with minimal additional processing complexity, avoiding the need to process the entire frame with the cross-fade operation
Data Source
Figure 1~2
Figure 3
Figure 4
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).