| 摘要 |
PURPOSE:To eliminate various types of noise disturbances in an electric wave transmitting route, by compressing the pitch of an audio signal to be transmitted to a low and narrow band. CONSTITUTION:An audio signal of a frequency fs supplied through a microphone 11 of a transmitter 10 receives a low-band pitch conversion into an audio signal of a frequency f's through the 1st audio pitch converter 13. This converted audio signal is then modulated by a modulator 14 and transmitted through an antenna 16 via a transmitting circuit 15. This electric wave is received at a receiver 20 together with the noises generated at a transmitting route. The received signal to be modulated and the noises are converted into intermediate frequencies through a mixing circuit 23 and then supplied to a narrow band filter 25 to reduce the noise greatly. Then an audio signal of the frequency f's and the noise of fn are obtained at the output side of a wave detecting circuit 26. These signal and noise are supplied to the 2nd audio pitch converter 27 to receive a high band pitch conversion into an audio signal of fs and the noise of f'n, respectively. |
