| 摘要 |
PURPOSE:To enable to correct and reject the code error at the reception side only, by using the redundancy band of telephone line in the 0-4kHz band, other than 0.3-3.4kHz, in the digital transmission of audio signal. CONSTITUTION:The audio digital signal in quadri-phase modulation is digital- coded for the amplitude of the in-phase and orthogonal components at the quadri- phase modulation detector 9,000 and enters the demodulator 5,000 and the error candidate detector 8,000. The output signal of the demodulator 5,000 including noise due to code error passes through the delay line 2,001 of the error rejection circuit 2,000 and is input to the subtractor 2,002. On the other hand, the output of the demodulator 5,000 passes through the error detection filter 1,000 and is input to the multiplier 2,003 after the signal outside the audio band of 0-0.3kHz and 3.4- 4kHz is extracted. The error candidate detection signal produced near the signal identification boundary line is delayed at the delay line 2,004 and enters the multplier 2,003, the output signal of the filter 1,000 is gated and input to the subtrator 2,002, to eliminate the noise due to the code error of demodulated output. |
