PURPOSE: To extract a frequency signal of degree N from a filter and then to measure it by measuring and setting the frequency of an untuned string to reference value (f1), by multiplying reference value (f1) by numeral N indicating the degree of the frequency of degree N, and by controlling filter characteristics on the basis of Nf1.
CONSTITUTION: String frequency extraction circuit 1 picks up the string frequency and then output signal (f) of a frequency corresponding to the frequency of the string. Then, VCF2 allows only frequency signal (fN) of degree N of a frequency corresponding to filter characteristic control signal CN to pass through. After converting signal (fN) into a digital signal of a corresponding frequency, divider circuit 3 divides it to output digital division signal DFN of degree N. Counter 4 counts the divided-wave signal by clock pulses to output frequency data (fd) of degree N. Then, N-degree frequency signal extraction control circuit 5 converts the data into an analog signal by multiplying data (fd) by numeral N indicating the degree to output above-mentioned filter control signal CN. Output circuit 6 outputs (fd) from counter 4 as the N-degree harmonic measurement frequency data after a certain time elapses since division signal DFD from divider circuit 3 is outputted.
ONODA TAKASHI
MORIYA KENICHI
