Resonant IIR lowpass (12dB/oct)¶
- Author or source: Olli Niemitalo
- Type: Resonant IIR lowpass (12dB/oct)
- Created: 2002-01-17 02:05:38
Hard to calculate coefficients, easy to process algorithm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | resofreq = pole frequency
amp = magnitude at pole frequency (approx)
double pi = 3.141592654;
/* Parameters. Change these! */
double resofreq = 5000;
double amp = 1.0;
DOUBLEWORD streamofs;
double w = 2.0*pi*resofreq/samplerate; // Pole angle
double q = 1.0-w/(2.0*(amp+0.5/(1.0+w))+w-2.0); // Pole magnitude
double r = q*q;
double c = r+1.0-2.0*cos(w)*q;
double vibrapos = 0;
double vibraspeed = 0;
/* Main loop */
for (streamofs = 0; streamofs < streamsize; streamofs++) {
/* Accelerate vibra by signal-vibra, multiplied by lowpasscutoff */
vibraspeed += (fromstream[streamofs] - vibrapos) * c;
/* Add velocity to vibra's position */
vibrapos += vibraspeed;
/* Attenuate/amplify vibra's velocity by resonance */
vibraspeed *= r;
/* Check clipping */
temp = vibrapos;
if (temp > 32767) {
temp = 32767;
} else if (temp < -32768) temp = -32768;
/* Store new value */
tostream[streamofs] = temp;
}
|
Comments¶
- Date: 2002-05-05 08:59:19
- By: moc.ibtta@suocuar
This looks similar to the low-pass filter I used in FilterKing (http://home.attbi.com/~spaztek4/) Can you cruft up a high-pass example for me?
Thanks,
__e
- Date: 2006-05-18 17:01:21
- By: faster init
thank you! works nicely...
here a simplified init version for faster changes of the filter properties for amps = 1.0
void init( double resofreq )
{
static const double FAC = pi * 2.0 /samplerate;
double q, w;
w = FAC * resofreq;
q = 1.0f - w /( ( 3.0 /( 1.0+w ) ) + w - 2.0 );
_r = q * q;
_c = r + 1.0f - 2.0f * cos(w) * q;
}