Adaptive Audio Compression for Target Loudness Range Control
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Solution Overview
Problem
Existing methods for controlling the loudness range of audio signals, such as Dynamic Range Control (DRC), face challenges in predicting the range of resulting gains and often require complex iterative processes, which can lead to suboptimal results and unpredictable audio quality.
Innovation Solution
An apparatus and method that evaluate the loudness of an input audio signal to determine a compressor transfer function based on a target loudness range and actual loudness values, minimizing the difference in mean loudness between the input and output signals, using a calculator to determine loudness range control gains and adjust the audio signal accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a compressor with a fixed preselected transfer function is applied to change the loudness range of the audio signal, then the loudness range is adjusted according to predefined criteria, but the target loudness range cannot be guaranteed at the output
Solution Approach 1:
The patent changes the parameters of the transfer function dynamically based on the characteristics of the input audio signal. Instead of using a fixed preselected transfer function, the system adapts the transfer function parameters (such as compression ratio, threshold, and knee) to match the specific loudness range and dynamic characteristics of the input signal, thereby guaranteeing the target loudness range at the output while maintaining ease of operation
Solution Approach 2:
The patent performs preliminary analysis of the input audio signal to determine its loudness range characteristics before applying the transfer function. This preliminary action includes measuring the input loudness range and using this information to pre-calculate the appropriate transfer function parameters, ensuring that the subsequent compression process achieves the desired target loudness range
2Adaptability or versatility
If a transfer function is determined based on a measured reference signal and volume control setting, then the transfer function adapts to the listening environment, but the complexity of the system increases
Solution Approach 1:
The patent extracts only the essential characteristics from the measured reference signal that are needed for transfer function determination, rather than processing the entire reference signal. By extracting key parameters such as ambient noise level and signal-to-noise ratio, the system achieves adaptability to the listening environment while keeping the processing complexity manageable
Solution Approach 2:
The patent performs preliminary measurement and analysis of the reference signal to extract relevant environmental characteristics before determining the transfer function. This preliminary action allows the system to adapt to different listening environments (such as late-night mode or high ambient noise) while maintaining a relatively simple processing architecture
3Manufacturing precision
If iterative processes are used to determine the transfer function, then the loudness range control can be optimized, but the processing time increases and results may be suboptimal
Solution Approach 1:
The patent performs preliminary calculation of the transfer function parameters based on the input signal characteristics and target loudness range requirements. By pre-determining the optimal transfer function parameters before applying compression, the system achieves precise loudness range control without requiring time-consuming iterative processes
Solution Approach 2:
The patent incorporates feedback mechanisms that allow the system to evaluate the effect of the transfer function in real-time and make adjustments if needed. This feedback approach ensures optimal results while minimizing processing time by only performing iterations when necessary, rather than using exhaustive iterative processes
4Ease of operation
If the dynamic range is reduced through automatic gain control, then the overall level of the audio signal is controlled, but the change in dynamic range is unpredictable
Solution Approach 1:
The patent uses feedback mechanisms to continuously monitor the dynamic range of the audio signal during processing. By measuring the actual dynamic range changes and comparing them against the target values, the system can adjust the transfer function parameters in real-time to ensure predictable and controlled dynamic range reduction, while maintaining ease of operation through automatic control
Data Source
AI summary
An apparatus for processing an input audio signal includes an evaluator for evaluating a loudness of the input audio signal to determine a loudness range and an actual loudness value. A calculator determines a compressor transfer function based on the determined loudness range, based on a target loudness range and based on the determined actual loudness value. The calculator further determines at least one loudness range control gain based on the determined compressor transfer function. An adjuster provides an output audio signal based on the input audio signal and based on the at least one determined loudness range control gain. The calculator is configured to determine the compressor transfer function such that a difference between a mean loudness of the output audio signal and a mean loudness of the input audio signal is minimized. A corresponding method is also provided.