Audio Loudness Metadata for Cross-Device Dynamic Range Control
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Solution Overview
Problem
Existing audio encoding systems are limited by preset dialnorm values and lack optimization for diverse playback devices and environments, leading to inaccurate loudness processing and degraded listening experiences due to reliance on user-set metadata and post-processing assumptions.
Innovation Solution
An audio processing system that includes pre-processing, encoding, and decoding units to normalize loudness and dynamic range across various devices by using loudness processing state metadata (LPSM) to adaptively adjust gain and ensure accurate playback, with mechanisms for validation and correction of metadata.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If preset dialnorm values are used for encoding, then the system is simple to operate, but the loudness processing accuracy deteriorates for diverse playback devices
Solution Approach 1:
The system changes the parameter representation from fixed preset dialnorm values to continuous LKFS (Loudness Knee Full Scale) values with 0.5 dB resolution. This allows precise representation of actual program loudness levels while maintaining systematic processing. The encoder measures actual loudness and encodes it as LPSM metadata, enabling accurate playback level determination for any playback device.
Solution Approach 2:
The system implements feedback by measuring the actual loudness of the encoded program and using that measurement to set the LPSM metadata value. This closed-loop approach ensures the metadata accurately reflects the program's true loudness characteristics, allowing decoders to make informed decisions about playback level adjustment based on the specific playback device being used.
2Adaptability or versatility
If a single audio bitstream is used for multiple playback scenarios, then the system has high versatility, but the loudness optimization for each device deteriorates
Solution Approach 1:
The system creates a universal LPSM metadata format that can be used across all playback devices while enabling device-specific optimization. The metadata contains the actual program loudness in LKFS, which can be interpreted differently by different device types (AVR, TV, mobile, etc.) to achieve optimal playback levels for each scenario. This single metadata structure serves multiple functions across diverse playback contexts.
Solution Approach 2:
The system applies local quality by allowing different playback devices to interpret the same LPSM metadata according to their specific characteristics and playback environments. Each device type can apply appropriate gain adjustments based on its own reference levels and capabilities, while all devices use the same source metadata, achieving device-optimized playback from a single encoded bitstream.
3Device complexity
If user-set metadata is relied upon, then the system requires minimal processing, but the reliability of loudness processing deteriorates
Solution Approach 1:
The system implements self-service by automatically measuring the loudness of the encoded program and populating the LPSM metadata field with the measured value. This eliminates the need for manual user input while ensuring the metadata accurately reflects the program's actual loudness characteristics. The encoder performs the measurement and sets the metadata automatically as part of the encoding process.
4Productivity
If post-processing assumptions are made, then the processing speed is high, but the accuracy of playback level adjustment deteriorates
Solution Approach 1:
The system performs preliminary action by measuring and encoding the actual program loudness in LPSM metadata during the encoding process, before playback occurs. This eliminates the need for assumptions during post-processing, as the decoder has advance knowledge of the program's true loudness level. The preliminary measurement and encoding enable accurate, assumption-free playback level adjustment on any device.
Data Source
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AI summary
Embodiments are directed to a method and system for receiving, in a bitstream, metadata associated with the audio data, and analyzing the metadata to determine whether a loudness parameter for a first group of audio playback devices are available in the bitstream. Responsive to determining that the parameters are present for the first group, the system uses the parameters and audio data to render audio. Responsive to determining that the loudness parameters are not present for the first group, the system analyzes one or more characteristics of the first group, and determines the parameter based on the one or more characteristics.