Audio Gain Metadata Transcoding for Clipping-Free Format Conversion
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Solution Overview
Problem
The challenge lies in transcoding audio metadata between different audio coding schemes, such as HE AAC, Dolby E, and Dolby Digital, to ensure that metadata remains undeteriorated and perceptually equivalent across various audio formats, particularly when framing and sample rates are incompatible, which is crucial for maintaining audio quality and compatibility in digital broadcasting systems.
Innovation Solution
A method for transcoding audio gain metadata involves selecting gain values based on the minimum gain values within a defined time interval, using a time constant that can be greater or equal to the maximum block length of both schemes to prevent gain overshoots, and allowing for interpolation curve selection based on the slope of the gain curve to match the source and target gain curves, ensuring that the transcoded gain values do not exceed the source values and maintain audio fidelity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gain values are directly transcoded without considering time intervals and minimum gain selection, then the transcoding process is simple and fast, but gain overshoots and clipping occur导致audio quality deterioration
Solution Approach 1:
The patent performs preliminary analysis of gain values within a time interval around the target time instance, selecting the minimum gain value in advance before applying it. This preliminary action prevents gain overshoots and clipping by ensuring the selected gain will not exceed the original audio signal levels, thereby maintaining audio quality without requiring complex real-time adjustment mechanisms.
Solution Approach 2:
The patent introduces dynamic selection of gain values based on time intervals and the characteristics of the gain curve (attack vs. release). By adaptively choosing different gain values from the first coding scheme depending on the temporal context and whether the gain is increasing or decreasing, the system maintains audio fidelity while accommodating the different temporal resolutions of the two coding schemes.
2Adaptability or versatility
If different coding schemes with incompatible framing are used, then versatility and adaptability are improved, but metadata deterioration and perceptual differences occur
Solution Approach 1:
The patent acts as an intermediary by selecting appropriate gain values from the first coding scheme that are compatible with the temporal structure of the second coding scheme. It mediates between the incompatible framing structures by performing time-aligned gain value selection, ensuring that the transcoded metadata maintains fidelity to the original audio while being compatible with the target coding scheme's temporal resolution.
Solution Approach 2:
The patent changes the parameter selection strategy by considering not just the gain value at the exact target time instance, but the minimum gain value within a surrounding time interval. This parameter change in the selection approach allows the system to adapt to different coding scheme temporal resolutions while maintaining metadata fidelity and preventing perceptual differences.
3Reliability
If the time constant is set to be greater than or equal to the maximum block length, then gain overshoots are prevented, but the responsiveness of gain changes is reduced
Solution Approach 1:
The patent dynamically adjusts the effective time constant based on whether the gain curve is in an attack or release phase. During attack phases, it uses a smaller effective time constant to maintain fast response and prevent excessive delay. During release phases, it can use a larger time constant to ensure smooth transitions and prevent clipping. This dynamic adjustment maintains both clipping prevention and responsive gain changes.
Data Source
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AI summary
The invention relates to the field of audio encoding. In particular, it relates to the transcoding of audio metadata between different audio coding schemes. It describes a method and a system for transcoding audio gain metadata related to dynamic range control from first gain metadata of a first audio coding scheme to second gain metadata of a second audio coding scheme, wherein the first and second audio coding schemes use coding blocks and wherein each coding block has at least one associated gain value. The method and the system select a gain value of the second gain metadata based on the gain values of the first gain metadata such that within a time interval around the time instance associated with the gain value of the second gain metadata, the minimum gain value of the first gain metadata is selected.