IIR 数字滤波器的设计

【实例简介】IIR 数字滤波器的设计 包括 Butterworth filter，Chebyshev I filter, Chebyshev II filter

形式有 Low Band， High Band，Pass Band， Stop Band

【实例截图】

【核心代码】

static void bwtf(int ln, int k, int n, double[] d, double[] c)
{
    int i;
    double pi, tmp;
    pi = 4.0 * Math.Atan(1.0);
    d[0] = 1.0;
    c[0] = 1.0;
    for (i = 1; i <= n; i )
    {
        d[i] = 0.0;
        c[i] = 0.0;
    }
    tmp = (k 1) - (ln 1.0) / 2.0;
    if (tmp == 0.0)
    {
        c[1] = 1.0;
    }
    else
    {
        c[1] = -2.0 * Math.Cos((2 * (k 1) ln - 1) * pi / (2 * ln));
        c[2] = 1.0;
    }
}
static void chebyi(int ln, int k, int n, double ep, double[] d, double[] c)
{
    int i;
    double pi, gam, omega, sigma;
    pi = 4.0 * Math.Atan(1.0);
    gam = Math.Pow((1.0 Math.Sqrt(1.0 ep * ep)) / ep, 1.0 / ln);
    sigma = 0.5 * (1.0 / gam - gam) * Math.Sin((2 * (k 1) - 1) * pi / (2 * ln));
    omega = 0.5 * (1.0 / gam gam) * Math.Cos((2 * (k 1) - 1) * pi / (2 * ln));
    for (i = 0; i <= n; i )
    {
        d[i] = 0.0;
        c[i] = 0.0;
    }
    if (((ln % 2) == 1) && ((k 1) == (ln 1) / 2))
    {
        d[0] = -sigma;
        c[0] = d[0];
        c[1] = 1.0;
    }
    else
    {
        c[0] = sigma * sigma omega * omega;
        c[1] = -2.0 * sigma;
        c[2] = 1.0;
        d[0] = c[0];
        if ((ln % 2 == 0) && (k == 0))
        {
            d[0] = d[0] / Math.Sqrt(1.0 ep * ep);
        }
    }
}
static void chebyii(int ln, int k, int n, double ws, double att, double[] d, double[] c)
{
    int i;
    double pi, gam, alpha, beta, sigma, omega, scln, scld;
    pi = 4.0 * Math.Atan(1.0);
    gam = Math.Pow((att Math.Sqrt(att * att - 1.0)), 1.0 / ln);
    alpha = 0.5 * (1.0 / gam - gam) * Math.Sin((2 * (k 1) - 1) * pi / (2 * ln));
    beta = 0.5 * (1.0 / gam gam) * Math.Cos((2 * (k 1) - 1) * pi / (2 * ln));
    sigma = ws * alpha / (alpha * alpha beta * beta);
    omega = -1.0 * ws * beta / (alpha * alpha beta * beta);
    for (i = 0; i <= n; i )
    {
        d[i] = 0.0;
        c[i] = 0.0;
    }
    if (((ln % 2) == 1) && ((k 1) == (ln 1) / 2))
    {
        d[0] = -1.0 * sigma;
        c[0] = d[0];
        c[1] = 1.0;
    }
    else
    {
        scln = sigma * sigma omega * omega;
        scld = Math.Pow((ws / Math.Cos((2 * (k 1) - 1) * pi / (2 * ln))), 2);
        d[0] = scln * scld;
        d[2] = scln;
        c[0] = d[0];
        c[1] = -2.0 * sigma * scld;
        c[2] = scld;
    }
}