| 摘要 |
PURPOSE:To set the cut-off frequency to the frequency being optimum for extracting a pitch by making the cut-off frequency of a low-pass filter means variable, detecting short time average power of sound signal obtained before and after they are allowed to pass through the low-pass filter means, respectively by a power detecting means, and controlling the cut-off frequency so that its ratio becomes constant. CONSTITUTION:A sound signal inputted from a microphone is allowed to pass through a low-pass filter 101 whose cut-off frequency is about 300Hz, to eliminate its high frequency component and inputted to plural comparators 1021 - 102n. Subsequently, binary signals by each threshold obtained by them are inputted to synchronous circuits 1031 - 103n, respectively, and synchronized with a reference clock generated by a clock generating circuit 104. Thereafter, the synchronized binary signals are sent to counting circuits 1051 - 105n, in which a time interval for transferring the signal from '0' to '1' is measured. Next, counted values of the circuits 105 are inputted through deciding circuits 1061 - 106n to an estimating circuit 107, in which a pitch period or a frequency of the input sound signal is estimated and whether it is optimum or not is decided. |
