Anti-spoofing

1. A speaker recognition system adapted for receiving audio data, the system being adapted for:

receiving audio data under test;

obtaining a Medium Frequency Relative Energy (MF) parameter, comprising a ratio between an energy of the received audio data under test in a predetermined frequency band and an energy of a complete frequency spectrum of the received audio data under test; and

classifying using a Gaussian classifier whether the received audio data under test is genuine or represents a recording replayed through a loudspeaker, based on the Medium Frequency Relative Energy (MF) parameter, wherein the Gaussian classifier is trained by the following steps:

a first Gaussian is obtained by:

receiving genuine audio data;

obtaining a first Medium Frequency Relative Energy (MF) parameter, comprising the ratio between the energy of the genuine audio data in a predetermined frequency band and the energy of the complete frequency spectrum of the genuine audio data;

receiving audio data representing recordings replayed through a loudspeaker; and

modelling the genuine audio data;

and wherein a second Gaussian is obtained by:

receiving audio data representing recordings replayed through a loudspeaker;

obtaining a second Medium Frequency Relative Energy (MF) parameter, comprising the ratio between the energy of the audio data representing recordings replayed through a loudspeaker in a predetermined frequency band and the energy of the complete frequency spectrum of the audio data representing recordings replayed through a loudspeaker; and

modelling the audio data representing recordings replayed through a loudspeaker with a second Gaussian.

2. A speaker recognition system according to claim 1 , wherein a lower end of the predetermined frequency band is in a range from 30 Hz to 150 Hz.

3. A speaker recognition system according to claim 1 , wherein an upper end of the predetermined frequency band is in a range from 150 Hz to 270 Hz.

4. A speaker recognition system according to claim 1 , wherein the considered parameters of the audio data further comprise a feature vector distance.

5. A speaker recognition system according to claim 4 , wherein the feature vector distance is calculated with regard to a constant value.

6. A speaker recognition system according to claim 4 , wherein the feature vector distance is calculated with regard to average feature vectors derived from enrolment data.

7. A speaker recognition system according to claim 1 , wherein the considered parameters of the audio data further comprise a spectral ratio.

8. A speaker recognition system according to claim 1 , wherein new parameters for the Gaussian classifier are found by adaptation of previous parameters of the Gaussian classifier using adaptation audio data.

9. A speaker recognition system according to claim 8 , wherein the number of available samples of adaptation audio data is considered in the adaptation process.

10. A speaker recognition system according to claim 8 , wherein mean vector(s) and/or covariance matrices and/or an a priori probability of one, two, three, four or more Gaussians representing the region of audio data parameters from genuine audio data and/or wherein mean vector(s) and/or the covariance matrices and/or an a priori probability of one, two, three, four or more Gaussians representing the region of audio data parameters from audio data representing recordings replayed through loudspeakers are adapted.

11. A speaker recognition system according to claim 8 , wherein enrollment audio data comprises the adaptation audio data.

12. A speaker recognition system according to claim 8 , wherein the adaptation audio data comprises genuine audio data and/or audio data representing a recording replayed through a loudspeaker.

13. A speaker recognition system according to claim 8 , wherein the adaptation audio data is chosen depending on information that the Gaussian classifier should model.

14. A method in a speaker recognition system for classifying whether audio data is genuine or represents a recording replayed through a loudspeaker, the method comprising:

receiving the audio data, and

classifying using a Gaussian classifier whether the received audio data is genuine or represents a recording replayed through a loudspeaker, wherein Gaussians are used to model a region of audio data parameters from genuine audio data and wherein Gaussians are used to model a region of audio data parameters from audio data representing recordings replayed through loudspeakers, based on a Medium Frequency Relative Energy (MF) parameter, and

wherein:

the Medium Frequency Relative Energy (MF) parameter comprises a ratio between an energy of the audio data in a predetermined frequency band and an energy of a complete frequency spectrum of the audio data; and

the Gaussian classifier is trained by the following steps:

a first Gaussian is obtained by:

receiving genuine audio data;

obtaining a first Medium Frequency Relative Energy (MF) parameter, comprising the ratio between the energy of the genuine audio data in a predetermined frequency band and the energy of the complete frequency spectrum of the genuine audio data;

receiving audio data representing recordings replayed through a loudspeaker; and

modelling the genuine audio data;

and wherein a second Gaussian is obtained by:

receiving audio data representing recordings replayed through a loudspeaker;

obtaining a second Medium Frequency Relative Energy (MF) parameter, comprising the ratio between the energy of the audio data representing recordings replayed through a loudspeaker in a predetermined frequency band and the energy of the complete frequency spectrum of the audio data representing recordings replayed through a loudspeaker; and

modelling the audio data representing recordings replayed through a loudspeaker with a second Gaussian.

15. A non-transitory computer-readable medium comprising computer-readable instructions that, when executed on a computer, are adapted to carry out a method according to claim 14 .

16. A speaker recognition system adapted for receiving audio data, the system being adapted for:

receiving audio data under test;

obtaining a Low Frequency Mel Frequency Cepstral Coefficients (LF-MFCC) parameter, comprising a ratio between an energy of the received audio data under test in a predetermined frequency band and an energy of a complete frequency spectrum of the received audio data under test; and

classifying using a Gaussian classifier whether the received audio data under test is genuine or represents a recording replayed through a loudspeaker, based on the Low Frequency Mel Frequency Cepstral Coefficients (LF-MFCC) parameter, wherein the Gaussian classifier is trained by the following steps:

a first Gaussian is obtained by:

receiving genuine audio data;

obtaining a first Low Frequency Mel Frequency Cepstral Coefficients (LF-MFCC) parameter, comprising the ratio between the energy of the genuine audio data in a predetermined frequency band and the energy of the complete frequency spectrum of the genuine audio data;

receiving audio data representing recordings replayed through a loudspeaker; and

modelling the genuine audio data;

and wherein a second Gaussian is obtained by:

receiving audio data representing recordings replayed through a loudspeaker;

obtaining a Low Frequency Mel Frequency Cepstral Coefficients (LF-MFCC) parameter, comprising the ratio between the energy of the audio data representing recordings replayed through a loudspeaker in a predetermined frequency band and the energy of the complete frequency spectrum of the audio data representing recordings replayed through a loudspeaker; and

modelling the audio data representing recordings replayed through a loudspeaker with a second Gaussian.

17. A speaker recognition system according to claim 16 , wherein the predetermined cut-off frequency is lower than 750 Hz.

18. A speaker recognition system according to claim 16 , wherein the considered parameters of the audio data further comprise a feature vector distance.

19. A speaker recognition system according to claim 18 , wherein the feature vector distance is calculated with regard to a constant value.

20. A speaker recognition system according to claim 18 , wherein the feature vector distance is calculated with regard to average feature vectors derived from enrolment data.

21. A speaker recognition system according to claim 18 , wherein the considered parameters of the audio data further comprise a spectral ratio.

22. A speaker recognition system according to claim 16 , wherein new parameters for the Gaussian classifier are found by adaptation of previous parameters of the Gaussian classifier using adaptation audio data.

23. A speaker recognition system according to claim 22 , wherein the number of available samples of adaptation audio data is considered in the adaptation process.

24. A speaker recognition system according to claim 22 , wherein mean vector(s) and/or covariance matrices and/or an a priori probability of one, two, three, four or more Gaussians representing the region of audio data parameters from genuine audio data and/or wherein mean vector(s) and/or the covariance matrices and/or an a priori probability of one, two, three, four or more Gaussians representing the region of audio data parameters from audio data representing recordings replayed through loudspeakers are adapted.

25. A speaker recognition system according to claim 22 , wherein enrollment audio data comprises the adaptation audio data.

26. A speaker recognition system according to claim 22 , wherein the adaptation audio data comprises genuine audio data and/or audio data representing a recording replayed through a loudspeaker.

27. A speaker recognition system according to claim 22 , wherein the adaptation audio data is chosen depending on the information that the Gaussian classifier should model.

28. A method in a speaker recognition system for classifying whether audio data is genuine or represents a recording replayed through a loudspeaker, the method comprising:

receiving the audio data, and

classifying using a Gaussian classifier whether the received audio data is genuine or represents a recording replayed through a loudspeaker, wherein Gaussians are used to model a region of audio data parameters from genuine audio data and wherein Gaussians are used to model a region of audio data parameters from audio data representing recordings replayed through loudspeakers, based on the Low Frequency Mel Frequency Cepstral Coefficients (LF-MFCC) parameter, and

wherein:

the Low Frequency Mel Frequency Cepstral Coefficients (LF-MFCC) parameter comprises 1, 2, 3 or more or all LF-MFCC extracted from a region of the audio data having frequencies lower than a predetermined cut-off frequency; and wherein the Gaussian classifier is trained by the following steps:

a first Gaussian is obtained by:

receiving genuine audio data;

obtaining a first Low Frequency Mel Frequency Cepstral Coefficients (LF-MFCC) parameter, comprising the ratio between the energy of the genuine audio data in a predetermined frequency band and the energy of the complete frequency spectrum of the genuine audio data;

receiving audio data representing recordings replayed through a loudspeaker; and

modelling the genuine audio data;

and wherein a second Gaussian is obtained by:

receiving audio data representing recordings replayed through a loudspeaker;

obtaining a Low Frequency Mel Frequency Cepstral Coefficients (LF-MFCC) parameter, comprising the ratio between the energy of the audio data representing recordings replayed through a loudspeaker in a predetermined frequency band and the energy of the complete frequency spectrum of the audio data representing recordings replayed through a loudspeaker; and

modelling the audio data representing recordings replayed through a loudspeaker with a second Gaussian.

29. A non-transitory computer-readable medium comprising computer-readable instructions that, when executed on a computer, are adapted to carry out a method according to claim 28 .

30. A speaker recognition system according to claim 16 , wherein the predetermined cut-off frequency is between 250 Hz and 750 Hz.