Filter Design Results

Generated by:   http://www-users.cs.york.ac.uk/~fisher/mkfilter

Summary

You specified the following parameters:

Results

Command line: /www/usr/fisher/helpers/mkfilter -Ch -7.0000000000e-02 -Lp -o 4 -a 4.4642857143e-01 0.0000000000e+00
raw alpha1    =   0.4464285714
raw alpha2    =   0.4464285714
warped alpha1 =   1.8734378073
warped alpha2 =   1.8734378073
gain at dc    :   mag = 1.497238168e+00   phase =   0.0000000000 pi
gain at centre:   mag = 1.497238168e+00   phase =  -0.8699514648 pi
gain at hf    :   mag = 0.000000000e+00

S-plane zeros:

S-plane poles:
	 -3.3566304357 + j  13.5623439769
	 -8.1036227218 + j   5.6177068128
	 -8.1036227218 + j  -5.6177068128
	 -3.3566304357 + j -13.5623439769

Z-plane zeros:
	 -1.0000000000 + j   0.0000000000	4 times

Z-plane poles:
	 -0.8992312710 + j   0.2551343016
	 -0.6975909913 + j   0.1681421798
	 -0.6975909913 + j  -0.1681421798
	 -0.8992312710 + j  -0.2551343016

Recurrence relation:
y[n] = (  1 * x[n- 4])
     + (  4 * x[n- 3])
     + (  6 * x[n- 2])
     + (  4 * x[n- 1])
     + (  1 * x[n- 0])

     + ( -0.4498778345 * y[n- 4])
     + ( -2.1450223211 * y[n- 3])
     + ( -3.8977979094 * y[n- 2])
     + ( -3.1936445246 * y[n- 1])

Ansi ``C'' Code

/* Digital filter designed by mkfilter/mkshape/gencode   A.J. Fisher
   Command line: /www/usr/fisher/helpers/mkfilter -Ch -7.0000000000e-02 -Lp -o 4 -a 4.4642857143e-01 0.0000000000e+00 -l */

#define NZEROS 4
#define NPOLES 4
#define GAIN   1.497238168e+00

static float xv[NZEROS+1], yv[NPOLES+1];

static void filterloop()
  { for (;;)
      { xv[0] = xv[1]; xv[1] = xv[2]; xv[2] = xv[3]; xv[3] = xv[4]; 
        xv[4] = next input value / GAIN;
        yv[0] = yv[1]; yv[1] = yv[2]; yv[2] = yv[3]; yv[3] = yv[4]; 
        yv[4] =   (xv[0] + xv[4]) + 4 * (xv[1] + xv[3]) + 6 * xv[2]
                     + ( -0.4498778345 * yv[0]) + ( -2.1450223211 * yv[1])
                     + ( -3.8977979094 * yv[2]) + ( -3.1936445246 * yv[3]);
        next output value = yv[4];
      }
  }

Download code and/or coefficients:

Magnitude (red) and phase (blue) vs. frequency

For an expanded view, enter frequency limits (as a fraction of the sampling rate) here:

Lower limit: Upper limit:

Impulse response

Step response

For a view on a different scale, enter upper time limit (integer number of samples) here:

Upper limit:

Tony Fisher fisher@minster.york.ac.uk