Linear predictive analysis apparatus, method, program and recording medium

1. A linear predictive analysis method for obtaining a coefficient which can be converted into a linear predictive coefficient corresponding to an input time series signal for each frame which is a predetermined time interval, the linear predictive analysis method comprising:

an autocorrelation calculating step of calculating autocorrelation R o (i) between an input time series signal X o (n) of a current frame and an input time series signal X o (n−i) i sample before the input time series signal X o (n) or an input time series signal X o (n+i) i sample after the input time series signal X o (n) for each of at least i=0, 1, . . . , P max ; and

a predictive coefficient calculating step of obtaining a coefficient which can be converted into linear predictive coefficients from the first-order to the P max -order using modified autocorrelation R′ o (i) obtained by multiplying the autocorrelation R o (i) by a coefficient for each corresponding i,

wherein the linear predictive analysis method further comprises a coefficient determining step of acquiring the coefficient from one coefficient table among coefficient tables t0, t1 and t2 using a period, an estimate value of the period, a quantization value of the period or a value having negative correlation with a fundamental frequency based on an input time series signal in the current frame or a past frame and a value having positive correlation with intensity of periodicity or a pitch gain assuming that a coefficient w t0 (i) is stored in the coefficient table t0, a coefficient w t1 (i) is stored in the coefficient table t1, and a coefficient w t2 (i) is stored in the coefficient table t2,

for at least part of i other than i=0, w t0 (i)<w t1 (i)≤w t2 (i), for at least part of each i among other i other than i=0, w t0 (i)≤w t1 (i)<w t2 (i), and for the remaining each i other than i=0, w t0 (i)≤w t1 (i)≤w t2 (i),

according to the period, the estimate value of the period, the quantization value of the period or the value having negative correlation with the fundamental frequency and the value having positive correlation with the intensity of periodicity or the pitch gain, (1) when the period is short and the pitch gain is large, a coefficient is acquired from the coefficient table t0 in the coefficient determining step, (9) when the period is long and the pitch gain is small, a coefficient is acquired from the coefficient table t2 in the coefficient determining step, (2) when the period is short and the pitch gain is medium, (3) when the period is short and the pitch gain is small, (4) when the period is medium and the pitch gain is large, (5) when the period is medium and the pitch gain is medium, (6) when the period is medium and the pitch gain is small, (7) when the period is long and the pitch gain is large, and (8) when the period is long and the pitch gain is medium, a coefficient is acquired from any of the coefficient tables t0, t1 and t2 in the coefficient determining step,

in at least one of (2), (3), (4), (5), (6), (7) and (8), a coefficient is acquired from the coefficient table t1 in the coefficient determining step, and

assuming that an identification number of a coefficient table tj k from which a coefficient is acquired in the coefficient determining step in the case of (k) where k=1, 2, . . . , 9 is j k , j 1 ≤j 2 ≤j 3 , j 4 ≤j 5 ≤j 6 , j 7 ≤j 8 ≤j 9 , j 1 ≤j 4 ≤j 7 , j 2 ≤j 5 ≤j 8 , and j 3 ≤j 6 ≤j 9 .

2. A linear predictive analysis method for obtaining a coefficient which can be converted into a linear predictive coefficient corresponding to an input time series signal for each frame which is a predetermined time interval, the linear predictive analysis method comprising:

an autocorrelation calculating step of calculating autocorrelation R o (i) between an input time series signal X o (n) of a current frame and an input time series signal X o (n−i) i sample before the input time series signal X o (n) or an input time series signal X o (n+i) i sample after the input time series signal X o (n) for each of at least i=0, 1, . . . , P max ; and

a predictive coefficient calculating step of obtaining a coefficient which can be converted into linear predictive coefficients from the first-order to the P max -order using modified autocorrelation R′ o (i) obtained by multiplying the autocorrelation R o (i) by a coefficient for each corresponding i,

wherein the linear predictive analysis method further comprises a coefficient determining step of acquiring the coefficient from one coefficient table among coefficient tables t0, t1 and t2 using a value having positive correlation with a fundamental frequency based on an input time series signal in the current frame or a past frame and a value having positive correlation with intensity of periodicity or a pitch gain assuming that a coefficient w t0 (i) is stored in the coefficient table t0, a coefficient w t1 (i) is stored in the coefficient table t1, and a coefficient w t2 (i) is stored in the coefficient table t2,

for at least part of i other than i=0, w t0 (i)<w t1 (i)≤w t2 (i), for at least part of each i among other i other than i=0, w t0 (i)≤w t1 (i)<w t2 (i), and for the remaining each i other than i=0, w t0 (i)≤w t1 (i)≤w t2 (i),

according to the value having positive correlation with the fundamental frequency and the value having positive correlation with the intensity of periodicity or the pitch gain, (1) when the fundamental frequency is high and the pitch gain is large, a coefficient is acquired from the coefficient table t0 in the coefficient determining step, (9) when the fundamental frequency is low and the pitch gain is small, a coefficient is acquired from the coefficient table t2 in the coefficient determining step, (2) when the fundamental frequency is high and the pitch gain is medium, (3) when the fundamental frequency is high and the pitch gain is small, (4) when the fundamental frequency is medium and the pitch gain is large, (5) when the fundamental frequency is medium and the pitch gain is medium, (6) when the fundamental frequency is medium and the pitch gain is small, (7) when the fundamental frequency is low and the pitch gain is large, and (8) when the fundamental frequency is low and the pitch gain is medium, a coefficient is acquired from any of the coefficient tables t0, t1 and t2 in the coefficient determining step,

in at least one of (2), (3), (4), (5), (6), (7) and (8), a coefficient is acquired from the coefficient table t1 in the coefficient determining step, and

assuming that an identification number of a coefficient table tj k from which a coefficient is acquired in the coefficient determining step in the case of (k) where k=1, 2, . . . , 9 is j k , j 1 ≤j 2 ≤j 3 , j 4 ≤j 5 ≤j 6 , j 7 ≤j 8 ≤j 9 , j 1 ≤j 4 ≤j 7 , j 2 ≤j 5 ≤j 8 , and j 3 ≤j 6 ≤j 9 .

3. A linear predictive analysis apparatus which obtains a coefficient which can be converted into a linear predictive coefficient corresponding to an input time series signal for each frame which is a predetermined time interval, the linear predictive analysis apparatus comprising:

processing circuitry configured to

calculate autocorrelation R o (i) between an input time series signal X o (n) of a current frame and an input time series signal X o (n−i) i sample before the input time series signal X o (n) or an input time series signal X o (n+i) i sample after the input time series signal X o (n) for each of at least i=0, 1, . . . , P max ; and

obtain a coefficient which can be converted into linear predictive coefficients from the first-order to the P max -order using modified autocorrelation R′ o (i) obtained by multiplying the autocorrelation R o (i) by a coefficient for each corresponding i,

wherein the processing circuitry further configured to acquire the coefficient from one coefficient table among coefficient tables t0, t1 and t2 using a period, an estimate value of the period, a quantization value of the period or a value having negative correlation with a fundamental frequency based on an input time series signal in the current frame or a past frame and a value having positive correlation with intensity of periodicity or a pitch gain assuming that a coefficient w t0 (i) is stored in the coefficient table t0, a coefficient w t1 (i) is stored in the coefficient table t1, and a coefficient w t2 (i) is stored in the coefficient table t2,

for at least part of i other than i=0, w t0 (i)<w t1 (i)≤w t2 (i), for at least part of each i among other i other than i=0, w t0 (i)≤w t1 (i)<w t2 (i), and for the remaining each i other than i=0, w t0 (i)≤w t1 (i)≤w t2 (i),

according to the period, the estimate value of the period, the quantization value of the period or the value having negative correlation with the fundamental frequency and the value having positive correlation with the intensity of periodicity or the pitch gain, (1) when the period is short and the pitch gain is large, a coefficient is acquired from the coefficient table t0 at the coefficient determining part, (9) when the period is long and the pitch gain is small, a coefficient is acquired from the coefficient table t2 at the coefficient determining part, (2) when the period is short and the pitch gain is medium, (3) when the period is short and the pitch gain is small, (4) when the period is medium and the pitch gain is large, (5) when the period is medium and the pitch gain is medium, (6) when the period is medium and the pitch gain is small, (7) when the period is long and the pitch gain is large, and (8) when the period is long and the pitch gain is medium, a coefficient is acquired from any of the coefficient tables t0, t1 and t2 by the processing circuitry,

in at least one of (2), (3), (4), (5), (6), (7) and (8), a coefficient is acquired from the coefficient table t1 by the processing circuitry, and

assuming that an identification number of a coefficient table tj k from which a coefficient is acquired by the processing circuitry in the case of (k) where k=1, 2, . . . , 9 is j k , j 1 ≤j 2 ≤j 3 , j 4 ≤j 5 ≤j 6 , j 7 ≤j 8 ≤j 9 , j 1 ≤j 4 ≤j 7 , j 2 ≤j 5 ≤j 8 , and j 3 ≤j 6 ≤j 9 .

4. A linear predictive analysis apparatus which obtains a coefficient which can be converted into a linear predictive coefficient corresponding to an input time series signal for each frame which is a predetermined time interval, the linear predictive analysis apparatus comprising:

processing circuitry configured to

calculate autocorrelation R o (i) between an input time series signal X o (n) of a current frame and an input time series signal X o (n−i) i sample before the input time series signal X o (n) or an input time series signal X o (n+i) i sample after the input time series signal X o (n) for each of at least i=0, 1, . . . , P max ; and

obtain a coefficient which can be converted into linear predictive coefficients from the first-order to the P max -order using modified autocorrelation R′ o (i) obtained by multiplying the autocorrelation R o (i) by a coefficient for each corresponding i,

wherein the processing circuitry further configured to acquire the coefficient from one coefficient table among coefficient tables t0, t1 and t2 using a value having positive correlation with a fundamental frequency based on an input time series signal in the current frame or a past frame and a value having positive correlation with intensity of periodicity or a pitch gain assuming that a coefficient w t0 (i) is stored in the coefficient table t0, a coefficient w t1 (i) is stored in the coefficient table t1, and a coefficient w t2 (i) is stored in the coefficient table t2,

for at least part of i other than i=0, w t0 (i)<w t1 (i)≤w t2 (i), for at least part of each i among other i other than i=0, w t0 (i)≤w t1 (i)<w t2 (i), and for the remaining each i other than i=0, w t0 (i)≤w t1 (i)≤w t2 (i),

according to the value having positive correlation with the fundamental frequency and the value having positive correlation with the intensity of periodicity or the pitch gain, (1) when the fundamental frequency is high and the pitch gain is large, a coefficient is acquired from the coefficient table t0 at the coefficient determining part, (9) when the fundamental frequency is low and the pitch gain is small, a coefficient is acquired from the coefficient table t2 by the processing circuitry, (2) when the fundamental frequency is high and the pitch gain is medium, (3) when the fundamental frequency is high and the pitch gain is small, (4) when the fundamental frequency is medium and the pitch gain is large, (5) when the fundamental frequency is medium and the pitch gain is medium, (6) when the fundamental frequency is medium and the pitch gain is small, (7) when the fundamental frequency is low and the pitch gain is large, and (8) when the fundamental frequency is low and the pitch gain is medium, a coefficient is acquired from any of the coefficient tables t0, t1 and t2 by the processing circuitry,

in at least one of (2), (3), (4), (5), (6), (7) and (8), a coefficient is acquired from the coefficient table t1 by the processing circuitry, and

assuming that an identification number of a coefficient table tj k from which a coefficient is acquired by the processing circuitry in the case of (k) where k=1, 2, . . . , 9 is j k , j 1 ≤j 2 ≤j 3 , j 4 ≤j 5 ≤j 6 , j 7 ≤j 8 ≤j 9 , j 1 ≤j 4 ≤j 7 , j 2 ≤j 5 ≤j 8 , and j 3 ≤j 6 ≤j 9 .

5. A non-transitory computer readable recording medium in which a program causing a computer to execute each step of the linear predictive analysis method according to claim 1 or 2 is recorded.