Patent ID: 7885808
Filing Date: 2011-02-08
Classification: G10G,G10H,G10L

Abstract:
1. A pitch-estimation method of estimating a pitch in terms of fundamental frequency, the method comprising the steps of: observing frequency components included in an input sound mixture and representing the observed frequency components as a probability density function given by an expression (a) where x is a log-scale frequency: obtaining a probability density function of a fundamental frequency F represented by an expression (b) from the probability density function of the observed frequency components: in the step of obtaining a probability density function of a fundamental frequency F, use of multiple tone models, tone model parameter estimation, and introduction of a prior distribution for model parameters being adopted, wherein obtaining, through computations using a computer, the weight ω in order to compute, using the computer, the parameter estimate represented by the expression (e) and the parameter estimate represented by the expression (f) using the estimates respectively represented by the expressions (g) and (h), the numerator of the expression (g) is expanded as a function of x given by an expression (m): where ω′ in order to iteratively compute the expressions (e) and (f) for obtaining the two parameter estimates for a predetermined number of times, after the frequency axis of the probability density function of the observed frequency components has been discretized, a first computation in computing the expressions (g) and (h) is performed for Nx times on each of frequencies x where Nx denotes a discretization number in a definition range for the frequency x; in the first computation, a second computation is performed on each of the M types of tone models in order to obtain a result of the expression (m), the result of the expression (m) is integrated with respect to the fundamental frequency F and the m-th tone model in order to obtain the denominator of each of the expressions (g) and (h), and the probability density function of the observed frequency components is assigned into the expressions (g) and (h), to thereby compute the expressions (g) and (h); in the second computation, a third computation is performed for H times corresponding to the number of the harmonic components including the frequency component of the fundamental frequency in order to obtain a result of an expression (n), and a result of the expression (m) is obtained by performing the summation of the results of the expression (n), changing the value of h from 1 to H: in the third computation, a fourth computation is performed for Na times with respect to the fundamental frequency F wherein x−(F+1200 log in the fourth computation, a result of an expression (o) is obtained using exp[−(x−(F+1200 log and the result of the expression (n) is obtained by multiplying the expression (o) by the old weight ω′