Method of comparing utterances for security control

A method of comparing a challenge verbal utterance with several enrollment verbal utterances from the same individual to determine a security action, the method comprising the steps of:

• A) preparing an enrollment data comprising the steps of:
• a) creating a Fast Fourier transform of an electrical signal representation of a verbal enrollment utterance to produce an enrollment frequency domain representation thereof;
• b) taking M enrollment samples of the enrollment frequency domain representation for each of N frequency channels to form an M by N enrollment matrix E;
• c) determining if at least X of the M enrollment samples have a selected minimum energy content in at least Y of the N frequency channels;
• d) repeating steps (a) through (c) if the determination at step (c) is negative, and aborting after a selected number of negative repeats of steps (a) through (c);
• e) repeating steps (a) through (c) if the determination at step (c) is positive, until a selected number of said sample enrollment matrices Ei are formed as E1, E2, E3, . . . ;
• f) calculating the sums of the differences EDi between each Ei, as ED1=(E1−E2)+(E1−E3)+ . . . , ED2=(E2−E1)+(E2−E3)+ . . . ;
• g) comparing the enrollment samples pairwise by moving each sample forward and backward in time to obtain a best match;
• h) calculating an enrollment span, ES, equal to the difference between the largest and the smallest value of EDi;
• and
• i) accepting the enrollment data if:
• i. ES<R1, and
• ii. EDi<R2 exists, where R1 and R2 are selected enrollment criterion,
• B) challenging the enrollment data comprising the steps of:
• a) creating a Fast Fourier transform of an electrical signal representation of a verbal challenge utterance to produce a challenge frequency domain representation thereof;
• b) taking M challenge samples of the challenge frequency domain representation for each of N frequency channels to form an M by N challenge matrix C;
• c) determining if at least X of the M challenge samples have a selected minimum energy content in at least Y of the N frequency channels;
• d) repeating steps (a) through (c) if the determination at step (c) is negative, and aborting after a selected number of negative repeats of steps (a) through (c);
• e) calculating the sums of the difference CDi between C and each Ei, as CD1=(C−E1)+(C−E2), CD2=(C−E2)+(C−E3), CD3=(C−E3)+(C−E4), . . . ;
• f) comparing each one of the challenge samples pairwise by moving a the samples forward and backward in time to obtain a best match;
• g) calculating a challenge span, CS, equal to the difference between the largest and the smallest value of CDi;
• and
• h) accepting the challenge data only if:
• i. CS<V1, and
• ii. CDi<V2, exists, where V1 and V2 are selected verification criterion,
• C) enabling the security action if the challenge verbal utterance is accepted.