Audio Loudness Normalization Using Compression Metadata
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Solution Overview
Problem
Portable devices often fail to reproduce audio content with consistent loudness and intelligibility across varying media formats and content types due to limitations in existing encoding and decoding standards, resulting in inadequate dynamic range and loudness levels.
Innovation Solution
The system employs dynamic range control and gain-limiting techniques to adjust audio signals, using differential or distinct dynamic range compression profiles, and metadata manipulation to enhance loudness and dynamic range on portable devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If existing encoding and decoding standards are used, then device compatibility is improved, but loudness consistency and intelligibility deteriorate
Solution Approach 1:
The system performs preliminary normalization of audio signals during the encoding stage, embedding normalized audio data and metadata into the encoded stream. This preliminary action ensures that the audio content is pre-adjusted for consistent loudness across different playback devices, eliminating the need for device-specific processing and achieving both compatibility and loudness consistency.
Solution Approach 2:
The patent introduces metadata as an intermediary element that carries normalization information between the encoder and decoder. This metadata acts as a mediator that guides the decoding process to reproduce audio with consistent loudness characteristics across varying media formats and content types, resolving the contradiction between device compatibility and loudness precision.
2Manufacturing precision
If dynamic range compression is applied, then loudness consistency is improved, but dynamic range deteriorates
Solution Approach 1:
The system applies dynamic range compression selectively to specific portions of the audio signal rather than uniformly across the entire signal. By applying compression only where needed to achieve loudness consistency while preserving the full dynamic range in other portions, the system resolves the contradiction between loudness consistency and dynamic range preservation.
Solution Approach 2:
The patent implements adaptive dynamic range compression that dynamically adjusts compression parameters based on the characteristics of the audio signal and playback environment. This dynamic approach allows the system to maintain loudness consistency across different conditions while preserving the natural dynamic range of the audio content, preventing excessive compression.
3Manufacturing precision
If gain-limiting techniques are used, then intelligibility is improved, but audio signal fidelity deteriorates
Solution Approach 1:
The system creates a normalized copy of the audio signal with improved intelligibility characteristics while preserving the original audio signal. The normalized copy is embedded as metadata or alternate audio stream, allowing playback systems to select between the original high-fidelity signal and the normalized intelligible signal, thus resolving the contradiction between intelligibility and fidelity.
Solution Approach 2:
The patent combines multiple audio signals with different characteristics (original high-fidelity signal and normalized intelligible signal) into a composite encoded stream. This composite structure allows decoding systems to selectively process or switch between different signal components, achieving both high fidelity and improved intelligibility simultaneously.
Data Source
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AI summary
Many portable playback devices cannot decode and playback encoded audio content having wide bandwidth and wide dynamic range with consistent loudness and intelligibility unless the encoded audio content has been prepared specially for these devices. This problem can be overcome by including with the encoded content some metadata that specifies a suitable dynamic range compression profile by either absolute values or differential values relative to another known compression profile. A playback device may also adaptively apply gain and limiting to the playback audio. Implementations in encoders, in transcoders and in decoders are disclosed.