Filter Design Results

Summary

filtertype	=	Butterworth
passtype	=	Lowpass
ripple	=
order	=	2
samplerate	=	44100
corner1	=	4800
corner2	=
adzero	=
logmin	=	-24

Results

Command line: /www/usr/fisher/helpers/mkfilter -Bu -Lp -o 2 -a 1.0884353741e-01 0.0000000000e+00
raw alpha1    =   0.1088435374
raw alpha2    =   0.1088435374
warped alpha1 =   0.1132939528
warped alpha2 =   0.1132939528
gain at dc    :   mag = 1.286717670e+01   phase =   0.0000000000 pi
gain at centre:   mag = 9.098467903e+00   phase =  -0.5000000000 pi
gain at hf    :   mag = 0.000000000e+00

S-plane zeros:

S-plane poles:
	 -0.5033517697 + j   0.5033517697
	 -0.5033517697 + j  -0.5033517697

Z-plane zeros:
	 -1.0000000000 + j   0.0000000000	2 times

Z-plane poles:
	  0.5357672835 + j   0.3087984635
	  0.5357672835 + j  -0.3087984635

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

     + ( -0.3824030731 * y[n- 2])
     + (  1.0715345670 * y[n- 1])

Ansi ``C'' Code

/* Digital filter designed by mkfilter/mkshape/gencode   A.J. Fisher
   Command line: /www/usr/fisher/helpers/mkfilter -Bu -Lp -o 2 -a 1.0884353741e-01 0.0000000000e+00 -l */

#define NZEROS 2
#define NPOLES 2
#define GAIN   1.286717671e+01

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

static void filterloop()
  { for (;;)
      { xv[0] = xv[1]; xv[1] = xv[2]; 
        xv[2] = next input value / GAIN;
        yv[0] = yv[1]; yv[1] = yv[2]; 
        yv[2] =   (xv[0] + xv[2]) + 2 * xv[1]
                     + ( -0.3824030731 * yv[0]) + (  1.0715345670 * yv[1]);
        next output value = yv[2];
      }
  }

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: