Downmix Limiting for Consistent Dialogue Level
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Solution Overview
Problem
Existing downmixing techniques face challenges in maintaining a consistent dialogue level while avoiding signal clipping, as gain limiting methods either lead to perceptible changes or worsen psychoacoustic fidelity.
Innovation Solution
The method involves deriving downmix coefficients by downscaling maximal coefficients with a common limiting factor across subgroups, allowing for more nuanced control over signal gain to prevent clipping while preserving dynamic and spatial properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gain limiting is applied locally at points where out-of-range values occur, then clipping is avoided, but gain changes become sudden and perceptible
Solution Approach 1:
The patent segments the audio signal processing into analysis blocks and applies limiting decisions block-by-block. By dividing the continuous signal into discrete blocks and making limiting decisions for each block independently, the system can control the timing and magnitude of gain changes, making them less perceptible while still preventing clipping.
Solution Approach 2:
The patent implements dynamic gain adjustment by calculating limiting factors based on the actual signal content of each block. The downmix coefficients are adjusted dynamically block-by-block according to the measured signal levels, allowing the system to adapt to changing signal conditions while maintaining smooth transitions.
2Difficulty of detecting and measuring
If gain limiting is applied over an extended time period, then perceptibility of gain changes is reduced, but dialogue level consistency deteriorates
Solution Approach 1:
The patent performs preliminary analysis of each block's signal characteristics before applying limiting. By pre-calculating the required limiting factor based on the block's content and the target dialogue level, the system can apply the exact amount of gain reduction needed, avoiding both excessive limiting (which hurts consistency) and insufficient limiting (which causes clipping).
Solution Approach 2:
The patent implements a feedback mechanism where the actual signal levels are measured, compared against target levels, and used to adjust the limiting factors for subsequent blocks. This closed-loop control ensures that dialogue level consistency is maintained while adapting to signal variations.
3Reliability
If downmix coefficients are reduced to prevent clipping, then signal range compliance is achieved, but psychoacoustic fidelity deteriorates
Solution Approach 1:
The patent applies limiting selectively based on the local signal characteristics of each block. Rather than applying a global gain reduction that would degrade all signal components uniformly, the system calculates individual limiting factors for each block, applying gain reduction only where and when necessary to prevent clipping while preserving psychoacoustic quality in blocks that don't require limiting.
Solution Approach 2:
The patent changes the downmix coefficients dynamically based on signal parameters. By adjusting the coefficients as a function of the measured signal levels and block characteristics, the system can maintain optimal psychoacoustic fidelity in most blocks while ensuring range compliance in blocks that would otherwise clip.
Data Source
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AI summary
The invention relates to downmixing techniques by which output audio signals are obtained from input audio signals partitioned into subgroups. A variable common gain limiting factor is applied to all downmix coefficients that govern the contributions from the input signals in a subgroup. While preserving the proportions between signal values within a subgroup, the invention makes it possible to limit the gain of different input signal subgroups to different extents, so that relatively more perceptible signals can be limited relatively less. It then becomes possible to achieve a consistent dialogue level while transitioning in a less perceptible fashion between signal portions with and without gain limiting. Embodiments of the invention include a method, a mixing system and a computer-program product.