Method and system of correcting spectral deformations in the voice, introduced by a communication network
First Claim
1. A method of correcting spectral deformations in a voice, introduced by a communication network, comprising an equalization operation on a frequency band, adapted to an actual distortion of a transmission chain, said operation being performed by a digital filter having a frequency response which is a function of a ratio between a reference spectrum and a spectrum corresponding to a long-term spectrum of voice signals of speakers, comprising:
- communicating a constitution of classes of speakers with one voice reference per class prior to the equalization of a voice signal of a speaker;
communicating a classification of the speaker, such that the speaker is allocated to the class from predefined classification criteria which causes a voice reference which is closest to the voice of the speaker to correspond to the speaker;
performing equalization of a digitized signal of the voice of the speaker with, as a reference spectrum, the voice reference of the class to which the speaker has been allocated;
wherein communicating the constitution of classes of speakers comprises selecting a corpus of N speakers recorded under non-deteriorated conditions, determining a long-term frequency spectrum of the selected corpus of N speakers, classifying the speakers of the corpus according to their partial cepstrum, and calculating the reference spectrum associated with each class to obtain the voice reference corresponding to each of the classes;
wherein said ceptrum is calculated from the long-term spectrum restricted to the equalization band and by applying a predefined classification criterion to these cepstra to obtain K classes.
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Abstract
A technique for correcting the voice spectral deformations introduced by a communication network. Prior to the operation of equalization of the voice signal of a speaker, the constitution of classes of speakers is communicated, with one voice reference per class. Then, for a given speaker, the classification of this speaker is communicated, that is to say his allocation to a class from predefined classification criteria in order to make a voice reference which is closest to his own correspond to him. Then, for that given speaker, communicating the equalization of the digitized signal of the voice of the speaker carried out with, as a reference spectrum, the voice reference of the class to which the speaker has been allocated. This technique applies to the correction of the timbre of the voice in switched telephone networks, in ISDN networks and in mobile networks.
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Citations
12 Claims
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1. A method of correcting spectral deformations in a voice, introduced by a communication network, comprising an equalization operation on a frequency band, adapted to an actual distortion of a transmission chain, said operation being performed by a digital filter having a frequency response which is a function of a ratio between a reference spectrum and a spectrum corresponding to a long-term spectrum of voice signals of speakers, comprising:
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communicating a constitution of classes of speakers with one voice reference per class prior to the equalization of a voice signal of a speaker; communicating a classification of the speaker, such that the speaker is allocated to the class from predefined classification criteria which causes a voice reference which is closest to the voice of the speaker to correspond to the speaker; performing equalization of a digitized signal of the voice of the speaker with, as a reference spectrum, the voice reference of the class to which the speaker has been allocated; wherein communicating the constitution of classes of speakers comprises selecting a corpus of N speakers recorded under non-deteriorated conditions, determining a long-term frequency spectrum of the selected corpus of N speakers, classifying the speakers of the corpus according to their partial cepstrum, and calculating the reference spectrum associated with each class to obtain the voice reference corresponding to each of the classes; wherein said ceptrum is calculated from the long-term spectrum restricted to the equalization band and by applying a predefined classification criterion to these cepstra to obtain K classes. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A system for correcting voice spectral deformations introduced by a communication network, comprising adapted equalization means in a frequency band, said adapted equalization means comprising:
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a digital filter having a frequency response which is a function of a ratio between a reference spectrum and a spectrum corresponding to a long-term spectrum of a voice signal; and signal processing means for calculating coefficients of the digital filter;
said signal processing means including;a first signal processing unit for calculating a modulus of a frequency response of an equalizer filter restricted to an equalization band according to the following relationship; wherein γ
ref(f) is the reference spectrum, which may be different from one speaker to another and which corresponds to a reference for a predetermined class to which a speaker belongs, L_RX is a frequency response of a reception line, S_RX is the frequency response of a reception signal and γ
x(f) is the long-term spectrum of an input signal of the filter; anda second signal processing unit for calculating a pulsed response from the calculated frequency response modulus to determine coefficients of the equalizer filter differentiated according to the constitution of different speaker classes;
wherein the classes of speakers are determined by selecting a corpus of N speakers recorded under non-deteriorated conditions, determining a long-term frequency spectrum of the N speakers of the selected corpus, classifying the speakers of the corpus according to their partial cepstrum by applying a predefined classification criterion to these cepstra to obtain K classes, and calculating the reference spectrum associated with each class to obtain the voice reference corresponding to each of the classes; and
wherein a partial cepstrum of a speaker is calculated from the speaker'"'"'s long-term spectrum restricted to the equalization band.- View Dependent Claims (9, 10, 11, 12)
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Specification