Accurate pitch measurement and tracking system and method

A pitch measurement system which determines the pitch of a quasi-periodic input signal, comprising:

• a signal sampler which samples said input signal's value x(t) during a sequence of sample periods;
• signal storage, coupled to said signal sampler, which stores a sequence of signal sample values representing said input signal's value during said sequence of sample periods;
• means, coupled to said signal storage, for generating an initial estimate P.multidot.T.sub.s of said input signal's period T.sub.0 where T.sub.s is the length of each said sample period and P is an integer;
• means for storing a set of 2M+1 coefficient values c(i), for i=-M to +M, where M is a positive integer;
• a finite impulse response (FIR) filter coupled to said signal storage for generating a predicted signal value x(k) for sampling period k in accordance with the following formula:
• ##EQU14## where x(k-P+i) is the stored signal sample value for sampling period k-P+i;
• error means for generating an error signal .epsilon.(k) corresponding to the difference between the actual stored signal value x(k) and the predicted signal value x(k);
• coefficient updating means for periodically updating said coefficient values so as to minimize said error signal .epsilon.(k)'s mean square value;
• and
• measurement output means for generating an output measurement equal to P.multidot.T.sub.s plus a phase delay value that is equal to a predefined function of said updated coefficient values.

A pitch measurement system which determines the pitch of a quasi-periodic input signal, comprising:

• a signal sampler which samples said input signal's value x(t) during a sequence of sample periods;
• signal storage, coupled to said signal sampler, which stores a sequence of signal sample values representing said input signal's value during said sequence of sample periods;
• a multiplicity of parallel signal pitch trackers, each said signal pitch tracker having assigned thereto an initial estimate P.multidot.T.sub.s of said input signal's period T.sub.0 where T.sub.s is the length of each said sample period and P is an integer;
• wherein a different value of P is assigned to each of said multiplicity of parallel signal pitch trackers;
• each said signal pitch tracker generating an estimated signal period value and an error signal value;
• monitoring means, coupled to said multiplicity of parallel signal pitch trackers, for monitoring said error signal values generated by said multiplicity of parallel signal pitch trackers and for outputting the estimated signal period value generated by the one of said signal pitch trackers with the lowest error signal value;
• each of said multiplicity of parallel signal pitch trackers including:
• means for storing a ordered set of N coefficient values, where N is a positive integer;
• a finite impulse response (FIR) filter coupled to said signal storage for generating a predicted signal value x(k) for a sampling period k by multiplying each of N of said stored signal sample values, selected in accordance with said initial estimate P.multidot.T.sub.s of said input signal's period, by corresponding ones of said N coefficient values and summing the resulting values;
• error means for generating an error signal .epsilon.(k) corresponding to the difference between the actual stored signal value x(k) for sampling period k and the predicted signal value x(k);
• coefficient updating means for periodically updating said coefficient values so as to minimize said error signal .epsilon.(k)'s mean square value;
• and
• output means for generating an output measurement equal to P.multidot.T.sub.s plus a phase delay value that is equal to a predefined function of said updated coefficient values.

A pitch measurement method which determines the pitch of a quasi-periodic input signal, the steps of the method comprising:

• sampling said input signal's value x(t) during a sequence of sample periods;
• storing a sequence of signal sample values representing said input signal's value during said sequence of sample periods;
• using said stored sequence of signal sample values, generating an initial estimate P.multidot.T.sub.s of said input signal's period T.sub.0 where T.sub.s is the length of each said sample period and P is an integer;
• storing an ordered set of N coefficient values, where N is a positive integer;
• selecting, in accordance with said initial estimate P.multidot.T.sub.s of said input signal's period, N of said stored signal sample values;
• (B) generating a predicted signal value x(k) for a sampling period k by multiplying each of said N selected signal sample values by corresponding ones of said N coefficient values and summing the resulting values;
• and (C) generating an error signal .epsilon.(k) corresponding to the difference between the actual stored signal value x(k) for sampling period k and the predicted signal value x(k);
• updating said coefficient values so as to minimize said error signal .epsilon.(k)'s means square value;
• and
• generating an output measurement equal to P.multidot.T.sub.s plus a phase delay value that is equal to a predefined function of said updated coefficient values.

A pitch measurement method which determines the pitch of a quasi-periodic input signal, the steps of the method comprising:

• sampling said input signal's value x(t) during a sequence of sample periods;
• storing a sequence of signal sample values representing said input signal's value during said sequence of sample periods;
• using said stored sequence of signal sample values, generating an initial estimate P.multidot.T.sub.s of said input signal's period T.sub.0 where T.sub.s is the length of each said sample period and P is an integer;
• storing a set of 2M+1 coefficient values c(i), for i=-M to +M, where M is a positive integer;
• selecting 2M+1 of said stored signal sample values corresponding to sample periods delayed from a current signal sample period k by periods ranging from (P-M)T.sub.s to (P+M)T.sub.s, generating a predicted signal value x(k) for sampling period k in accordance with the following formula:
• ##EQU15## where x(k-P+i) is the stored signal sample value for sampling period k-P+i, and generating an error signal .epsilon.(k) corresponding to the difference between the actual stored signal value x(k) and the predicted signal value x(k);
• updating said coefficient values so as to minimize said error signal .epsilon.(k)'s means square value;
• and
• generating an output measurement equal to P.multidot.T.sub.s plus a phase delay value that is equal to a predefined function of said updated coefficient values.