Filter Design Results

Summary

filtertype	=	Butterworth
passtype	=	Highpass
ripple	=
order	=	4
samplerate	=	44100
corner1	=	4500
corner2	=
adzero	=
logmin	=	-18

Results

Command line: /www/usr/fisher/helpers/mkfilter -Bu -Hp -o 4 -a 1.0204081633e-01 0.0000000000e+00
raw alpha1    =   0.1020408163
raw alpha2    =   0.1020408163
warped alpha1 =   0.1056861637
warped alpha2 =   0.1056861637
gain at dc    :   mag = 0.000000000e+00
gain at centre:   mag = 1.662970801e+00   phase =  -1.0000000000 pi
gain at hf    :   mag = 2.351795860e+00   phase =   0.0000000000 pi

S-plane zeros:
	  0.0000000000 + j   0.0000000000	4 times

S-plane poles:
	 -0.2541193072 + j  -0.6134982778
	 -0.6134982778 + j  -0.2541193072
	 -0.6134982778 + j   0.2541193072
	 -0.2541193072 + j   0.6134982778

Z-plane zeros:
	  1.0000000000 + j   0.0000000000	4 times

Z-plane poles:
	  0.6521459075 + j  -0.4496606128
	  0.5161811627 + j  -0.1474234400
	  0.5161811627 + j   0.1474234400
	  0.6521459075 + j   0.4496606128

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

     + ( -0.1808276723 * y[n- 4])
     + (  1.0236624164 * y[n- 3])
     + ( -2.2621673461 * y[n- 2])
     + (  2.3366541405 * y[n- 1])

Ansi ``C'' Code

/* Digital filter designed by mkfilter/mkshape/gencode   A.J. Fisher
   Command line: /www/usr/fisher/helpers/mkfilter -Bu -Hp -o 4 -a 1.0204081633e-01 0.0000000000e+00 -l */

#define NZEROS 4
#define NPOLES 4
#define GAIN   2.351795860e+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]
                     + ( -0.1808276723 * yv[0]) + (  1.0236624164 * yv[1])
                     + ( -2.2621673461 * yv[2]) + (  2.3366541405 * yv[3]);
        next output value = yv[4];
      }
  }

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

• x axis: frequency, as a fraction of the sampling rate (i.e. 0.5 represents the Nyquist frequency, which is 22050 Hz)
• y axis (red): magnitude (logarithmic, normalized)
• y axis (blue): phase

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

Impulse response

• x axis: time, in samples (i.e. 44100 represents 1 second)
• y axis (red): filter response (linear, normalized)

Step response

• x axis: time, in samples (i.e. 44100 represents 1 second)
• y axis (red): filter response (linear, normalized)

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