| 摘要 |
A CPU measures the interval between the zero-crossing points at the two ends of a waveform element a having, e.g., a positive polarity. Thereafter, the CPU sequentially measures the interval between the zero-crossing points at the two ends of each of waveform elements b, c, and d having the same polarity. Upon detection of the waveform element d which is almost equal in interval to the waveform element a and is located nearest thereto in terms of time, the interval between the start points (zero-crossing points) of the waveform elements a and d is extracted as the pitch period of the input waveform. Subsequently, the above-described series of operations is repeated.
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