Controllable Bass Post-Filter Tuning to Reduce Audio Artifacts
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Solution Overview
Problem
Existing audio signal processing techniques using bass post-filters in speech coding often introduce artifacts, particularly when dealing with music or noisy speech, and rely on suboptimal control methods such as pitch information or complete deactivation, which fail to enhance audio quality effectively.
Innovation Solution
A controllable bass post-filter with a variable characteristic, controlled by a bass post-filter control parameter, is used to optimize the filtering process by calculating an optimal attenuation factor using a minimum mean square error estimator and transmitting this parameter within the bitstream, allowing for precise adjustment of the gain and filter characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bass post-filter is applied to enhance speech quality, then speech clarity is improved, but artifacts are introduced in music or noisy speech
Solution Approach 1:
The bass post-filter is made dynamically controllable through a filter characteristic parameter that can be adjusted based on signal type detection. The system transitions from a static filter to a dynamic one that adapts its characteristics, enabling it to enhance speech when appropriate while avoiding artifacts in music or noisy speech conditions.
Solution Approach 2:
The invention changes the filter characteristic parameter to optimize the bass post-filter's performance. By modifying parameters such as the filter cutoff frequency and gain based on the detected signal type, the system achieves better speech enhancement without introducing harmful artifacts in non-speech conditions.
2Object-generated harmful factors
If bass post-filter is completely deactivated to avoid artifacts, then artifacts are reduced, but audio quality enhancement is lost
Solution Approach 1:
Instead of complete deactivation, the system implements dynamic control where the bass post-filter remains active but its characteristics are adjusted. The filter characteristic parameter enables the filter to adapt its behavior, maintaining audio quality enhancement while minimizing artifacts through signal-type-dependent parameter adjustment.
3Ease of operation
If pitch information is used to control bass post-filter, then control is simplified, but audio quality enhancement is suboptimal
Solution Approach 1:
The invention introduces a filter characteristic parameter that goes beyond simple pitch information. This parameter is determined through a more sophisticated process involving signal type detection and optimization, providing better audio quality enhancement while maintaining practical control through parameter indexing and lookup tables.
Solution Approach 2:
The system implements feedback mechanisms where the filter characteristic parameter is optimized based on the actual signal characteristics. The encoder analyzes the input signal and adjusts the parameter accordingly, creating a closed-loop control system that improves audio quality while keeping the decoder implementation simple through parameter transmission.
Data Source
AI summary
An apparatus for processing an encoded signal, the encoded signal having an encoded audio signal having information on a pitch delay or a pitch gain, and a bass post-filter control parameter, has: an audio signal decoder for decoding the encoded audio signal using the information on the pitch delay or the pitch gain to obtain a decoded audio signal; a controllable bass post-filter for filtering the decoded audio signal to obtain a processed signal, wherein the controllable bass post-filter has the variable bass post-filter characteristic controllable by the bass post-filter control parameter; and a controller for setting the variable bass post-filter characteristic in accordance with the bass post-filter control parameter included in the encoded signal.