巴特沃斯带通滤波器 c++代码

以下是一个简单的巴特沃斯带通滤波器的C代码：

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

#define PI 3.14159265358979323846

#define SAMPLE_RATE 44100.0 // 采样率
#define LOW_CUTOFF 1000.0 // 低截止频率
#define HIGH_CUTOFF 4000.0 // 高截止频率
#define Q_FACTOR 0.707 // 品质因数

double b0, b1, b2, a1, a2; // 滤波器系数

void calculateCoefficients() {
    double omega_low = 2.0 * PI * LOW_CUTOFF / SAMPLE_RATE;
    double omega_high = 2.0 * PI * HIGH_CUTOFF / SAMPLE_RATE;
    double alpha = sin(omega_high) * sinh(log(2.0) / 2.0 * Q_FACTOR * omega_high / sin(omega_high));
    double a = pow(10.0, log10(2.0) / 2.0 * Q_FACTOR);
    double beta = sqrt(a * a - 1.0) / tan(omega_low / 2.0);
    double b0_top = a * (alpha + beta);
    double b1_top = 0.0;
    double b2_top = a * (alpha - beta);
    double a0_top = 1.0 + beta / alpha + a * a;
    double a1_top = 2.0 * (a * a - 1.0);
    double a2_top = 1.0 - beta / alpha + a * a;
    b0 = b0_top / a0_top;
    b1 = b1_top / a0_top;
    b2 = b2_top / a0_top;
    a1 = a1_top / a0_top;
    a2 = a2_top / a0_top;
}

double filter(double input) {
    static double x1 = 0.0, x2 = 0.0, y1 = 0.0, y2 = 0.0;
    double output = b0 * input + b1 * x1 + b2 * x2 - a1 * y1 - a2 * y2;
    x2 = x1;
    x1 = input;
    y2 = y1;
    y1 = output;
    return output;
}

int main() {
    calculateCoefficients();
    double input = 0.0;
    double output = 0.0;
    while (1) {
        printf("Enter input: ");
        scanf("%lf", &input);
        output = filter(input);
        printf("Output: %lf\n", output);
    }
    return 0;
}

该代码使用了巴特沃斯滤波器的公式来计算滤波器系数，并使用差分方程来实现滤波器的运算。在主循环中，每次从终端读取一个输入，对其进行滤波，并将滤波后的输出打印到终端。