Audio Compensation Filters for Consistent Loudness Across Playback Levels
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Solution Overview
Problem
Existing audio processing technologies fail to accurately compensate for variations in human loudness perception across different playback volumes, leading to uneven audio quality, particularly at low or high frequencies.
Innovation Solution
A system that uses a loudness estimator to determine both the production and playback loudness levels of an audio signal, generating a compensation filter based on equal-loudness contours to apply differential gains and maintain consistent perceived loudness across varying playback volumes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If bass and treble boost is applied to compensate for human loudness perception at low playback volumes, then perceived audio quality is improved, but excessive bass boost causes distortion and speaker damage
Solution Approach 1:
The patent implements dynamic equalization filters that automatically adjust bass and treble boost levels based on the detected playback volume. At low playback volumes, moderate boost is applied to compensate for reduced human auditory sensitivity, while at high playback volumes, the boost is reduced or eliminated to prevent distortion and speaker damage. This dynamic adaptation resolves the contradiction by making the compensation level dependent on the operating conditions.
Solution Approach 2:
The system changes the equalization parameters (bass and treble gain levels) based on the playback volume level. The loudness compensation contour is adjusted dynamically, applying stronger high-frequency and low-frequency boost only when necessary at low volumes, and reducing or disabling this boost at higher volumes to avoid harmful effects on speakers and distortion.
2Manufacturing precision
If loudness compensation filter is applied to maintain consistent perceived loudness across frequency ranges, then audio quality is improved, but system complexity increases
Solution Approach 1:
The patent pre-calculates and stores loudness compensation contours for multiple playback volume levels before operation. During actual use, the system simply detects the current playback volume and selects the corresponding pre-computed filter settings, avoiding the need for complex real-time calculations. This preliminary preparation reduces computational complexity while maintaining accurate loudness compensation across different volume levels.
Solution Approach 2:
The patent replaces complex mechanical loudness compensation circuitry with digital signal processing. Instead of using analog equalization circuits that would require multiple physical components and manual adjustments, the system uses digital filters implemented in software or firmware, which can be dynamically adjusted without adding physical complexity to the hardware architecture.
3Manufacturing precision
If differential gains are applied to compensate for human loudness perception variations, then perceived loudness consistency is improved, but measurement and implementation difficulty increases
Solution Approach 1:
The patent incorporates a playback level detector that continuously monitors the actual playback volume and uses this feedback to dynamically adjust the equalization filter settings. The system detects the playback level, selects the appropriate loudness compensation contour from pre-stored options, and applies the corresponding differential gains. This feedback loop automates the complex process of matching equalization settings to playback conditions, reducing implementation difficulty while maintaining accurate loudness compensation.
Data Source
AI summary
Provided are, among other things, systems, methods and techniques for loudness-based audio-signal compensation. According to one such system, an input line accepts an input audio signal; a loudness estimator, coupled to the input line, processes the input audio signal to obtain an audio playback loudness level and also provides a production loudness level for the input audio signal; and a filter generator/selector coupled to an output of the loudness estimator provides an audio compensation filter based on the production loudness level and the audio playback loudness level. The input signal is processed by the audio compensation filter to provide an output signal.