Specific Loudness Processing for Level-Dependent Spectral Balance
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Solution Overview
Problem
Current methods for measuring and controlling perceived sound loudness and spectral balance in audio signals are inadequate, as they fail to accurately account for the non-linearity of loudness growth with sound pressure level and do not compensate for changes in perceived spectral balance across different acoustic levels, leading to inaccuracies in loudness assessment and spectral balance adjustments.
Innovation Solution
The solution involves deriving modification parameters to control the specific loudness of audio signals by modifying them to approximate a target specific loudness, using psychoacoustic models and filters that simulate the human ear's response, thereby reducing differences in perceived loudness and spectral balance, especially in the presence of background noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional loudness measurement methods are used, then the measurement process is simple, but the measurement precision is insufficient due to failure to account for non-linearity of loudness growth and spectral balance changes
Solution Approach 1:
The patent segments the audio signal into multiple critical bands corresponding to different frequency regions. By analyzing loudness contributions from each band separately and then combining them, the system achieves more accurate overall loudness measurement while accounting for the non-linear perception characteristics of different frequency regions.
Solution Approach 2:
The patent applies frequency-dependent gain adjustments to compensate for the non-linear growth of loudness with sound pressure level. By dynamically changing the weighting parameters across different frequency bands based on the measured signal levels, the system accurately tracks perceived loudness changes while maintaining a manageable computational framework.
2Ease of operation
If standard volume control is applied, then the operation is simple, but the perceived spectral balance deteriorates at different acoustic levels
Solution Approach 1:
The patent implements frequency-dependent volume control by applying different gain factors to different critical bands. This allows the system to maintain constant perceived spectral balance across varying volume levels by selectively adjusting gains in frequency regions where the ear's sensitivity changes most with level, while keeping the control interface simple.
Solution Approach 2:
The patent dynamically adjusts the equalization parameters based on the instantaneous loudness level of the audio signal. As the signal level changes, the system automatically modifies the frequency-dependent gains to compensate for level-dependent spectral balance shifts, providing adaptive correction that operates transparently during playback.
3Measurement precision
If loudness compensation is applied, then the perceived loudness accuracy improves, but the device complexity increases due to additional processing requirements
Solution Approach 1:
The patent processes the audio signal through a bank of band-pass filters corresponding to critical bands, analyzing loudness in each segment separately. This segmentation approach enables accurate loudness measurement by capturing frequency-dependent perception effects while organizing the computation into manageable, parallel processing stages.
Solution Approach 2:
The patent implements a multi-functional processing system that simultaneously performs loudness measurement, spectral balance analysis, and volume control adjustment. By integrating these functions into a unified framework that operates on the same critical band decomposition, the system achieves accurate loudness compensation without proportionally increasing complexity.
Data Source
AI summary
The invention relates to the measurement and control of the perceived sound loudness and/or the perceived spectral balance of an audio signal. An audio signal is modified in response to calculations performed at least in part in the perceptual (psychoacoustic) loudness domain. The invention is useful, for example, in one or more of: loudness-compensating volume control, automatic gain control, dynamic range control (including, for example, limiters, compressors, expanders, etc.), dynamic equalization, and compensating for background noise interference in an audio playback environment. The invention includes not only methods but also corresponding computer programs and apparatus.