Adaptive loudness levelling for digital audio signals
First Claim
1. A method for adaptive loudness levelling, comprising:
- receiving a plurality of audio input signals;
weighting one or more frequencies associated with each audio input signal according to human audio perception;
characterizing a state for each audio input signal;
detecting whether each audio input signal is experiencing an event;
producing a target levelling gain for each audio input signal based on the characterized state and/or detected event;
temporally masking the target levelling gain; and
combining the temporally masked target levelling gain with a delayed plurality of audio input signals.
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Abstract
A time-domain method of adaptively levelling the loudness of a digital audio signal is proposed. It selects a proper frequency weighting curve to relate the volume level to the human auditory system. The audio signal is segmented into frames of a suitable duration for content analysis. Each frame is classified to one of several predefined states and events of perceptual interest is detected. Four quantities are updated each frame according to the classified state and detected event to keep track of the signal. One quantity measures the long-term loudness and is the main criterion for state classification of a frame. The second quantity is the short-term loudness that is mainly used for deriving the target gain. The third quantity measures the low-level loudness when the signal is deemed to not contain important content, giving a reasonable estimate of noise floor. A fourth quantity measures the peak loudness level that is used to simulate the temporal masking effect. The target gain to maintain the audio signal to the desired loudness level is calculated by a volume leveller, regulated by a gain controller that simulates the temporal masking effect to get rid of unnecessary gain fluctuations, ensuring a pleasant sound.
14 Citations
20 Claims
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1. A method for adaptive loudness levelling, comprising:
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receiving a plurality of audio input signals; weighting one or more frequencies associated with each audio input signal according to human audio perception; characterizing a state for each audio input signal; detecting whether each audio input signal is experiencing an event; producing a target levelling gain for each audio input signal based on the characterized state and/or detected event; temporally masking the target levelling gain; and combining the temporally masked target levelling gain with a delayed plurality of audio input signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for modifying digital audio signal amplitude to maintain consistent loudness, comprising:
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relating a volume level of a plurality of audio input signals to human perception using a weighting curve; computing a volume levelling target gain by tracking a plurality of audio signal attributes for each of the audio input signals wherein tracking includes classifying a state of each of the audio input signals and detecting whether each of the audio input signals is associated with an event; applying the volume levelling target gain to a delayed audio input signal producing a consistent loudness level; and temporally masking the target levelling gain and combining the temporally masked target levelling gain with a delayed plurality of audio input signals. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification