Pitch Post-Filter for Low-Rate Audio Coding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing audio coders face challenges in achieving optimal performance at low rates due to noisy outputs and architectural limitations, particularly in predictive coding, where post-filters are difficult to implement effectively without causing artifacts.
Innovation Solution
A method for determining post-filter parameters by decomposing signal error into signal-correlated and uncorrelated noise components, evaluating a criterion that balances distortion and noise reduction, and using a paired-zero filter design for pitch prediction to enhance audio signal processing, allowing for efficient post-filtering without pre-filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a post-filter is applied to reduce noise in predictive audio coding, then noise reduction is improved, but signal-correlated distortion increases
Solution Approach 1:
The patent applies parameter changes by adapting the post-filter characteristics based on the analyzed audio signal properties. The filter parameters are modified according to the signal's periodicity and spectral characteristics, allowing optimal noise reduction while minimizing distortion of the original audio content.
Solution Approach 2:
The patent implements feedback by analyzing the decoded audio signal to determine appropriate post-filter parameters. The system continuously monitors the signal quality and adjusts the post-filter accordingly, creating a closed-loop system that balances noise reduction with preservation of signal integrity.
2Object-affected harmful factors
If post-filtering is applied to enhance audio quality, then noise reduction is improved, but system delay increases
Solution Approach 1:
The patent applies preliminary action by performing signal analysis and post-filter parameter determination before the actual filtering operation. The system pre-analyzes the decoded audio segments to determine optimal filter parameters in advance, enabling faster filtering execution and reducing overall system delay.
3Productivity
If pre-filtering is used instead of post-filtering, then processing speed is improved, but audio quality degradation occurs
Solution Approach 1:
The patent applies the inversion principle by reversing the conventional approach and using post-filtering instead of pre-filtering. The system processes the decoded audio signal after the predictive coding stage, applying filters that compensate for the specific characteristics of the decoded signal, thereby achieving both acceptable processing speed and improved audio quality.
Data Source
AI summary
Methods and systems for using pitch predictors in speech/audio coders are provided. Techniques for optimal pre- and post-filtering are presented, and a general result that post-filtering is more effective than pre-filtering is derived. A practical paired-zero filter design for the low-rate regime is proposed, and this design is extended to handle frequency-dependent periodicity levels. Further, the methods described provide a general performance measure for a post-filter that only uses information available at the decoder, thereby allowing for the optimization or selection of a post-filter without increasing the rate.