Acoustic wave communication system and receiver

An acoustic wave communication system comprising:

• a transmitter having a frequency modulator that modulates the frequency of a signal in a frequency band receivable by a microphone based on transmission data thereby to generate a transmission signal, and an acoustic wave generator that generates an acoustic wave in response to the transmission signal generated by the frequency modulator;
• and
• a receiver having a microphone that receives the acoustic wave output from the acoustic wave generator of the transmitter, an unnecessary signal remover that signal-processes the received signal from the microphone to remove unnecessary signal components, and an FM detector that restores the transmission data by FM detection of the received signal from which unnecessary signal components have been removed by the unnecessary signal remover,
• the unnecessary signal remover, provided in the receiver, comprising:
• a first filter section that extracts a signal component corresponding to the transmission signal generated by the frequency modulator, from the received signal input from the microphone;
• a frequency converter that converts the frequency of the received signal that has passed through the first filter section to an predetermined intermediate frequency band;
• a second filter section that extracts a signal component corresponding to the transmission signal generated by the frequency modulator, from the signal of which frequency has been converted by the frequency converter;
• an envelope detector that detects an envelope of the received signal that has passed through the first filter section;
• a third filter section that extracts unnecessary signal components having a lower frequency than that of the received signal that has passed through the second filter section, from the signal of which envelope has been detected by the envelope detector, and,
• a remover that removes the unnecessary signal components that have passed through the third filter section from the received signal that has passed through the second filter section.