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我为音频信号的频率调制编写了以下代码。音频本身为 1 秒长，以 8000 Hz 采样。我想通过使用频率为 50 Hz（表示为采样频率的一小部分）的正弦波将 FM 应用于此音频信号。调制信号的调制指数为0.25，从而只产生一对边带。

for (i = 0; i < 7999; i++) {
    phi_delta = 8000 - 8000 * (1 + 0.25 * sin(2* pi * mf * i));
    f_phi_accum += phi_delta; //this can have a negative value
    /*keep only the integer part that'll be used as an index into the input array*/
    i_phi_accum = f_phi_accum;   
    /*keep only the fractional part that'll be used to interpolate between samples*/
    r_phi_accum = f_phi_accum - i_phi_accum; 
    //If I'm getting negative values should I convert them to positive
    //r_phi_accum = fabs(f_phi_accum - i_phi_accum);   
    i_phi_accum = abs(i_phi_accum);
    /*since i_phi_accum often exceeds 7999 I have to add this if statement so as to      prevent out of bounds errors   */  
    if (i_phi_accum < 7999)
        output[i] = ((input[i_phi_accum] + input[i_phi_accum + 1])/2) * r_phi_accum;            
}
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1 回答 1

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您对 phi_delta 的计算偏离了 8000 倍和一个偏移量 - 它应该是 1 +/- 一个小值，即

phi_delta = 1.0 + 0.25 * sin(2.0 * pi * mf * i));

这将导致 phi_delta 的范围为 0.75 到 1.25。

于 2011-12-30T09:53:32.740 回答