| 摘要 |
PROBLEM TO BE SOLVED: To effectively eliminate aliasing noises although an ultrasonograph is so simple in arrangement that its costs can be made very low. SOLUTION: An interpolating circuit 31 interpolates a predetermined value into a line of digital data about the forward and reverse components of a stereo sound created, so that the data interval matches a sampling frequency sufficiently higher than the audible frequency of a D/A converter 33. Thereafter, the data are passed through a digital FIR filter 32 to eliminate the aliasing noises resulting from sampling carried out each time an ultrasonic scan is repeated. After the data are converted into analog signals by the D/A converter 33, the signals are passed through a simple analog low-pass filter 34 for elimination of the aliasing noises resulting from the D/A conversion.
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