EP0424016A2
Expired / Lapsed
EP
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Perceptual coding of audio signals
Assignee: AT&T Inc
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Filing: 1990-10-10
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Granted: —
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Expires: 2010-10-10
Abstract
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.
Inventors
- 👤 Karlheinz Brandenburg
- 👤 James David Johnston
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 21:54
CPC Classifications
H; H03; H03M; H03M7/00; H04; H04B; H04B1/00; H04B1/66; H04B1/665
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
132 words
A method of processing an ordered time sequence of audio signals partitioned into blocks of samples, each such block having a discrete short-time spectrum, S(ω i ), i=1, 2,...,N, for each of said blocks, CHARACTERIZED IN THAT said method comprises 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, 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 .
Claim 2
Independent Claim
132 words
A method of processing an ordered time sequence of audio signals partitioned into blocks of samples, each such block having a discrete short-time spectrum, S(ω i ), i=1, 2,...,N, for each of said blocks, CHARACTERIZED IN THAT said method comprises 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, 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 .
Claim 3
Dependent Claim
26 words
The method of claim 1 further CHARACTERIZED IN THAT quantizing said S(ω i ) based on said noise masking threshold at each respective ω i .
Claim 4
Dependent Claim
55 words
The method of claim 1 further CHARACTERIZED IN THAT said step of predicting comprises, for each ω i , forming the difference between the value of S(ω i ) for the corresponding ω i from the two preceding blocks, and adding said difference to the value for S(ω i ) from the immediately preceding block.
Claim 5
Dependent Claim
40 words
The method of claim 3, CHARACTERIZED IN THAT wherein said S(ω i ) is represented in terms of its magnitude and phase, and wherein said difference and adding are effected separately for the magnitude and phase of S(ω i ).
Claim 6
Dependent Claim
36 words
The method of claim 1, CHARACTERIZED IN THAT said determining of said randomness metric is accomplished by calculating the euclidian distance between said estimate of S(ω i ) and said actual value for S(ω i ).
Claim 7
Dependent Claim
47 words
The method of claim 5, CHARACTERIZED IN THAT said determining of said randomness metric further comprises normalizing said euclidian distance with respect to the sum of the magnitude of said actual magnitude for S(ω i ) and the absolute value of said estimate of S(ω i ).
Claim 8
Dependent Claim
77 words
The method of claim 1, CHARACTERIZED IN THAT said estimating of the noise masking threshold at each ω i comprises determining the energy of said audio signal at ω i spreading said energy values at a given ω i to one or more adjacent frequencies, thereby to generate a spread energy spectrum, determining a desired noise level at each ω i based on said tonality function and said spread energy spectrum for the respective ω i .
Claim 9
Dependent Claim
39 words
The method of claim 7, wherein said estimating of the noise masking threshold function further comprises modifying said threshold function in response to an absolute noise masking threshold for each ω i to form a limited threshold function. function.
Claim 10
Dependent Claim
34 words
The method of claim 8, CHARACTERIZED IN THAT said method further comprising modifying said limited threshold function to eliminate any existing pre-echoes, thereby generating an output threshold function value for each ω i .
Claim 11
Independent Claim
80 words
The method of any of claims 1, 7, 8 or 9, further CHARACTERIZED IN THAT said method further comprising the steps of generating an estimate of the number of bits necessary to encode S(ω i ) quantizing said S(ω i ) to form quantized representations of said S(ω i ) using said estimate of the number of bits, and providing to a medium a coded representation of said quantized values and information describing about how said quantized values were derived.
Claim 12
Independent Claim
108 words
A method for decoding 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 represent said audio signal with reduced perceptual error, CHARACTERIZED IN THAT said method comprises 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.
Claim 13
Independent Claim
108 words
A method for decoding 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 represent said audio signal with reduced perceptual error, CHARACTERIZED IN THAT said method comprises 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.
Claim 14
Dependent Claim
22 words
The method of claim 11 CHARACTERIZED IN THAT said reconstructing comprises using said second signals to effect scaling of said quantized values.
Claim 15
Dependent Claim
21 words
The method of claim 11 CHARACTERIZED IN THAT said reconstructing comprises applying a global gain factor based on said second signals.
Claim 16
Dependent Claim
21 words
The method of claim 11 CHARACTERIZED IN THAT said reconstructing comprises determining quantizer step size as a function of frequency component.
Claim 17
Dependent Claim
26 words
The method of claim 11 CHARACTERIZED IN THAT said second signals include information about the degree of coarseness of quantization as a function of frequency component.
Claim 18
Dependent Claim
27 words
The method of claim 11 CHARACTERIZED IN THAT said second signals include information about the number of values of said audio signal that occur in each block.
References Cited (Backward Citations)
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