Multichannel Audio Loudness Scaling Without Spatial Balance Loss
Solution Overview
Problem
Existing methods for adjusting the loudness of multichannel audio signals often disrupt the perceived spatial balance by applying a single gain to all channels, causing quieter channels to fall below the hearing threshold and altering the intended diffuse spatial balance.
Innovation Solution
Scaling the perceived loudness of each individual channel by a consistent amount to maintain the relative loudness between channels, while optionally applying a correction to minimize errors in overall loudness scaling, thereby preserving the spatial balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single gain is applied to all channels to adjust overall loudness, then the overall perceived loudness is adjusted efficiently, but the relative perceived loudness between channels changes, disrupting spatial balance
Solution Approach 1:
The patent divides the multichannel audio signal into individual channel components and processes each channel separately. By calculating and applying individual gains to each channel based on its specific loudness characteristics, the system maintains relative loudness relationships between channels while achieving overall loudness adjustment, thus preserving spatial balance.
Solution Approach 2:
The patent applies different gain adjustments to different channels based on their local loudness characteristics. Each channel receives a tailored gain value calculated from its specific loudness measurement, allowing precise control over each channel's contribution to the overall spatial balance while efficiently adjusting the total loudness.
2Ease of operation
If a single gain is applied to all channels, then the adjustment process is simple and fast, but quieter channels may fall below the hearing threshold, degrading audio quality
Solution Approach 1:
The system segments the audio processing into channel-specific operations, measuring loudness and calculating gains for each channel individually. This segmentation enables the simple application of pre-calculated gains while preventing quiet channels from falling below the hearing threshold, as each channel's gain is specifically tailored to its characteristics.
3Manufacturing precision
If individual channel loudness is scaled by a consistent amount, then the relative perceived loudness between channels is maintained, but the overall loudness scaling may have calculation errors
Solution Approach 1:
The patent employs an iterative feedback process where initial individual channel gains are calculated and applied, then the actual overall loudness is measured and compared to the target loudness. Based on this feedback, correction factors are computed and applied to adjust the individual channel gains, eliminating calculation errors and achieving precise overall loudness scaling while maintaining relative loudness consistency.
Data Source
AI summary
Scaling, by a desired amount sm, the overall perceived loudness Lm of a multichannel audio signal, wherein perceived loudness is a nonlinear function of signal power P, by scaling the perceived loudness of each individual channel Lc by an amount substantially equal to the desired amount of scaling of the overall perceived loudness of all channels sm, subject to accuracy in calculations and the desired accuracy of the overall perceived loudness scaling sm. The perceived loudness of each individual channel may be scaled by changing the gain of each individual channel, wherein gain is a scaling of a channel's power. Optionally, in addition, the loudness scaling applied to each channel may be modified so as to reduce the difference between the actual overall loudness scaling and the desired amount of overall loudness scaling.