| 摘要 |
PURPOSE:To make a noise caused by switching unaudible by attenuating a noise exceeding an audio frequency contained in an output of a sample holding circuit SH by a low-pass filter LF, and making only an acoustic signal pass through so that an acoustic signal whose noise has been eliminated is generated in an output terminal Vt. CONSTITUTION:A sound volume change instruction is supplied to a terminal (a) of a pulse generating circuit PG by a manual operation as shown in a figure (a), and a sampling pulse and a clock pulse of a frequency exceeding an audio frequency as shown in sigures (b), (c) are generated from terminals (b), (c). A sample holding circuit SH is provided with an analog switch consisting of an MOS. FET and generates a noise as shown in a figure (f) when a state of the analog switch is switched at the time of a rise and a fall of the sampling pulse. In this case, since the sampling pulse is set in advance to a frequency exceeding of an audio frequency of >= about 20kHz, a frequency of the noise exceeds the audio frequency and does not become a trouble in an auditory sense. |
