虚拟低音谐波信号产生的算法C代码

以下是一个简单的虚拟低音谐波信号产生算法的C代码：

#include <stdio.h>
#include <math.h>

#define SAMPLE_RATE 44100
#define FREQ_LOW 40
#define FREQ_HIGH 80
#define Q_FACTOR 1.5
#define AMPLITUDE 0.5

double lowpass_filter(double input, double prev_output, double cutoff_freq, double q_factor)
{
    double omega_c = 2 * M_PI * cutoff_freq / SAMPLE_RATE;
    double alpha = sin(omega_c) / (2 * q_factor);
    double b0 = (1 - cos(omega_c)) / 2;
    double b1 = 1 - cos(omega_c);
    double b2 = (1 - cos(omega_c)) / 2;
    double a0 = 1 + alpha;
    double a1 = -2 * cos(omega_c);
    double a2 = 1 - alpha;
    double output = (b0 / a0) * input + (b1 / a0) * prev_output + (b2 / a0) * (prev_output - a1 * input) + (a2 / a0) * prev_output;
    return output;
}

int main()
{
    double freq = (FREQ_LOW + FREQ_HIGH) / 2.0;
    double cutoff_freq = FREQ_LOW / sqrt(2);
    double q_factor = Q_FACTOR;
    double amplitude = AMPLITUDE;
    double phase = 0.0;
    double prev_output = 0.0;
    int num_samples = 44100;
    int i;

    for (i = 0; i < num_samples; i++) {
        double input = amplitude * sin(2 * M_PI * freq * i / SAMPLE_RATE + phase);
        double output = lowpass_filter(input, prev_output, cutoff_freq, q_factor);
        printf("%f\n", output);
        prev_output = output;
    }

    return 0;
}

该算法使用一个二阶低通滤波器来产生虚拟低音谐波信号。它首先生成一个合适的频率，然后将其低通滤波器的截止频率设置为所需的低频范围的中心频率。滤波器的Q因子也可以进行调整以控制滤波器的斜率。最后，算法使用一个简单的正弦波作为输入，将其送入滤波器并输出滤波器的响应。该算法产生的输出可以直接写入音频文件中，以产生虚拟低音谐波信号。