巴特沃斯带通滤波器 c++代码

以下是一个基本的巴特沃斯带通滤波器的C代码实现：

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

// 定义滤波器参数
#define ORDER 4
#define FS 1000.0
#define F_LOW 50.0
#define F_HIGH 200.0

// 定义全局变量
double a[ORDER+1];
double b[ORDER+1];
double x[ORDER+1];
double y[ORDER+1];

void butterworth_bandpass(double fl, double fh, double fs, int order, double* b, double* a) {
    double w1 = 2 * fl / fs;
    double w2 = 2 * fh / fs;
    double bw = w2 - w1;
    double r = cos(bw/2) / sin(bw/2);
    double theta = M_PI / (2 * order);
    double s = sin(theta);
    double c = cos(theta);
    double alpha = s / (2 * r);
    double beta = sqrt(1 - 4 * pow(alpha, 2));
    double a0 = 1 + alpha;
    double a1 = -2 * c;
    double a2 = 1 - alpha;
    double b0 = alpha;
    double b1 = 0;
    double b2 = -alpha;
    double a_den = a0 + a1 + a2;
    a[0] = a0 / a_den;
    a[1] = a1 / a_den;
    a[2] = a2 / a_den;
    b[0] = b0 / a_den;
    b[1] = b1 / a_den;
    b[2] = b2 / a_den;
}

double butterworth_filter(double x_new) {
    double y_new = b[0] * x_new + b[1] * x[1] + b[2] * x[2] - a[1] * y[1] - a[2] * y[2];
    x[2] = x[1];
    x[1] = x_new;
    y[2] = y[1];
    y[1] = y_new;
    return y_new;
}

int main() {
    // 初始化滤波器参数
    butterworth_bandpass(F_LOW, F_HIGH, FS, ORDER, b, a);
    // 初始化输入信号和输出信号
    double x_in[100];
    double y_out[100];
    for (int i = 0; i < ORDER; i++) {
        x[i] = 0;
        y[i] = 0;
    }
    // 生成测试信号
    for (int i = 0; i < 100; i++) {
        x_in[i] = sin(2 * M_PI * F_LOW / FS * i) + 0.5 * sin(2 * M_PI * F_HIGH / FS * i);
        y_out[i] = 0;
    }
    // 应用滤波器
    for (int i = 0; i < 100; i++) {
        y_out[i] = butterworth_filter(x_in[i]);
    }
    // 输出结果
    for (int i = 0; i < 100; i++) {
        printf("%f\t%f\n", x_in[i], y_out[i]);
    }
    return 0;
}

注：该代码仅供参考，实际应用中需要根据具体的需求进行修改。