Perceptual coding of audio signals
First Claim
1. A method of processing an ordered time sequence of audio signals partitioned into contiguous blocks of samples, each such block having a discrete short-time spectrum, S(ω
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i), i=1, 2, . . . N, for each of said blocks, comprisingpredicting, for each block, an estimate of the values for each S(ω
i) based on the values for S(ω
i) for one or more prior blocks,determining for each frequency, ω
i, a randomness metric based on the predicted value for each S(ω
i) and the actual value for S(ω
i) for each block,based on said randomness metrics, and the distribution of power with frequency in the block, determining the value of a tonality function as a function of frequency, andbased on said tonality function, estimating the noise masking threshold at each ω
i.
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Abstract
A method is disclosed for determining estimates of the perceived noise masking level of audio signals as a function of frequency. By developing a randomness metric related to the euclidian distance between (i) actual frequency components amplitude and phase for each block of sampled values of the signal and (ii) predicted values for these components based on values in prior blocks, it is possible to form a tonality index which provides more detailed information useful in forming the noise masking function. Application of these techniques is illustrated in a coding and decoding context for audio recording or transmission. The noise spectrum is shaped based on a noise threshold and a tonality measure for each critical frequency-band (bark).
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Citations
16 Claims
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1. A method of processing an ordered time sequence of audio signals partitioned into contiguous blocks of samples, each such block having a discrete short-time spectrum, S(ω
-
i), i=1, 2, . . . N, for each of said blocks, comprising
predicting, for each block, an estimate of the values for each S(ω
i) based on the values for S(ω
i) for one or more prior blocks,determining for each frequency, ω
i, a randomness metric based on the predicted value for each S(ω
i) and the actual value for S(ω
i) for each block,based on said randomness metrics, and the distribution of power with frequency in the block, determining the value of a tonality function as a function of frequency, and based on said tonality function, estimating the noise masking threshold at each ω
i. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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i), i=1, 2, . . . N, for each of said blocks, comprising
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11. A method for processing an ordered sequence of coded signals comprising
first code signals representing values of the frequency components of a block of values of an audio signal and second code signals representing information about how said first signals were derived to reproduce said audio signal with reduced perceptual error, said method comprising using said second signals to determine quantizing levels for said audio signal which reflect a reduced level of perceptual distortion, reconstructing quantized values for said frequency content of said audio signal in accordance with said quantizing levels, and transforming said reconstructed quantized spectrum to recover an estimate of the audio signal.
Specification