EP0446037A2
Expired / Lapsed
EP
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Hybrid perceptual audio coding
Assignee: AT&T Inc
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Filing: 1991-03-06
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Granted: —
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Expires: 2011-03-06
Abstract
Abstract A hybrid coding technique for high quality coding of audio signals, using a subband filtering technique further refined to achieve a large number of subbands. Noise masking thresholds for subbands are then determined using a new tonality measure applicable to individual frequency bands or single frequencies. Based on the thresholds so determined, input signals are coded to achieve high quality at reduced bit rates.
Inventors
- 👤 Karlheinz Brandenburg
- 👤 James David Johnston
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-04 16:41
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/66; H04B1/665; H03; H03M; H03M1/00; H03M1/12
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
91 words
A method of processing an ordered time sequence of audio signals partitioned into blocks of samples, said method comprising determining a discrete short-time spectrum, S(ω i ), i=1, 2,...,N, for each of said blocks, determining the value of a tonality function as a function of frequency, and based on said tonality function, estimating the noise masking threshold for each of ω i , CHARACTERIZED IN THAT said step of determining S(ω i ) comprises determining S(ω i ) with differing time and frequency resolution as a function of ω i ,
Claim 2
Dependent Claim
32 words
The method of claim 1 further CHARACTERIZED IN THAT said step of determining S(ω i ) comprises determining S(ω i ) with frequency and time resolution approximating that of human auditory response.
Claim 3
Dependent Claim
92 words
The method of claim 1 further CHARACTERIZED IN THAT 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 respective ones of the predicted value for S(ω i ) and the actual value for S(ω i ) for each block, said method further comprises the step of quantizing said S(ω i ) based on said noise masking threshold at respective ω i .
Claim 4
Dependent Claim
55 words
The method of claim 3 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
38 words
The method of claim 4, CHARACTERIZED IN THAT said S(ω i ) is represented in terms of its magnitude and phase, and said difference and adding are effected separately for both magnitude and phase of S(ω i ).
Claim 6
Dependent Claim
36 words
The method of claim 3, 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 6, 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
84 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 , and said method further comprises spreading said energy values at a given ω i to one or more adjacent frequencies, thereby to generate a spread energy spectrum, and 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
38 words
The method of claim 8, 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.
Claim 10
Dependent Claim
34 words
The method of claim 9, 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, 8, 9 or 10, 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
118 words
A method for decoding an ordered sequence of coded signals comprising first code signals representing values of the frequency components corresponding to 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, 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, CHARACTERIZED IN THAT said frequency components have variable rime and frequency resolution.
Claim 13
Dependent Claim
37 words
The method of claim 12 CHARACTERIZED IN THAT said second signals identify the variation of said resolution as a function of frequency, and said reconstructing comprises using said second signals to effect scaling of said quantized values.
Claim 14
Dependent Claim
21 words
The method of claim 12 CHARACTERIZED IN THAT said reconstructing comprises applying a global gain factor based on said second signals.
Claim 15
Dependent Claim
21 words
The method of claim 12 CHARACTERIZED IN THAT said reconstructing comprises determining quantizer step size as a function of frequency component.
Claim 16
Dependent Claim
26 words
The method of claim 12 CHARACTERIZED IN THAT said second signals include information about the degree of coarseness of quantization as a function of frequency component.
Claim 17
Dependent Claim
27 words
The method of claim 12 CHARACTERIZED IN THAT said second signals include information about the number of values of said audio signal that occur in each block.
Claim 18
Dependent Claim
92 words
Apparatus for processing an ordered time sequence of audio signals partitioned into blocks of samples comprising, means for determining a discrete short-time spectrum, S(ω i ), i=1, 2,...,N, for each of said blocks, means for determining the value of a tonality function as a function of frequency, and means for estimating the noise masking threshold for each of ω i , in response to said tonality function, said means for determining further comprises means for determining S(ω i ) with dithering time and frequency resolution at different values of ω i ,
Claim 19
Dependent Claim
32 words
The method of claim 1 further CHARACTERIZED IN THAT said means for determining S(ω i ) comprises determining S(ω i ) with frequency and time resolution approximating that of human auditory response.
Claim 20
Dependent Claim
38 words
The apparatus of claim 18 CHARACTERIZED IN THAT said means for determining S(ω i ) comprises means for partitioning said audio signal into a plurality of frequency subband, and means for determining the short-time spectrum for each subband.
Claim 21
Dependent Claim
17 words
The apparatus of claim 20 CHARACTERIZED IN THAT said means for partitioning comprises quadrature mirror filter means.
Claim 22
Dependent Claim
22 words
The apparatus of claim 21 CHARACTERIZED IN THAT said quadrature mirror filter means comprises a tree structural array of quadrature mirror filters.
References Cited (Backward Citations)
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