| 摘要 |
PROBLEM TO BE SOLVED: To measure a backgound noise level in a narrow audible area generated by audio demodulated from ultrasound and adjust an output volume of audio, depending on the background noise level, even during outputting of the audio. SOLUTION: An audio signal from a sound source 1 is modulated by a modulator 2 to generate a super directional audio signal indicating audio in which ultrasound is a carrier. A sound field 7 of demodulated audio is generated by emitting ultrasound from a parametric loudspeaker 4 based on the super directional audio signal amplified by an amplifier 3. A microphone 5 is provided in the sound field 7, and a background noise detection/volume controller 6 extracts background noise 8 from an output signal of the microphone 5 using the audio signal from the sound source 1 and controls the modulator 2 to generate the super directional audio signal having a volume, depending on a level of the background noise 8, while the microphone 5 is prevented from collecting ambient ultrasound using an acoustic filter 9 which attenuates ultrasound. COPYRIGHT: (C)2007,JPO&INPIT
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