(1) to find an audio file, read with audioread, on the basis of the original sampling rate, 100 times by interpolation method to improve the sampling rate, draw waveform and power spectrum (pwelch function), (2) of the waveform AM modulation, a carrier cycle 16 sampling, waveform and power spectrum, (3) to the DSB modulation of the waveform, a carrier cycle 16 sampling, waveform and power spectrum, (4) of the DSB modulation waveform phase error of dual orthogonal coherent demodulation, draw waveform after demodulation, and compared with the original waveform,