Akso - Audio DSP Platform

multiladder

$\text{[math]}$

nth order lowpass and bandpass filter (max filters=32) freq sets cutoff center frequency spread spreads the cutoff frequencies between cascaded filters (for HP inversed), so can be seen as slope-control. BW spreads the highpass and lowpass filters apart res sets the resonance level LPcasc sets the TOTAL amount of filters HP sets after how many lowpass filters, highpass filters are used. If higher then LPcasc, all filters are lowpass. feed sets which filter output is used for the resonance. Resonance path is saveguarded by the same code that's used for the "fatbasters" distortion module. gain boosts the resonance in the feedback loop->adds upper harmonics to the resonating signal. "max" sets the max level of the resonance (so it cannot go out of control)

Author: Remco van der Most

License: BSD

Github: sss/filter/multiladder.axo

Inlets

frac32buffer input

frac32 cutoff frequency

frac32 spread

frac32 BW

frac32.positive res

Outlets

frac32buffer output

Parameters

frac32.u.map freq

frac32.u.map BW

frac32.u.map res

frac32.u.map gain

frac32.u.map max

frac32.s.map spread

int32 LP

int32 HP

int32 feed

Declaration

int32_t val[33];
int32_t vil[33];
int32_t f[33];
int32_t g[33];
int i;
int32_t resonance;
int32_t volsat;
int32_t volres;
int32_t vola;

Init

for (i = 0; i < 33; i++) {
  val[i] = 0;
}

Control Rate

for (i = 0; i <= (param_LP + param_HP); i++) {
  if (i > 0)
    MTOF(inlet_BW + param_BW + param_freq + inlet_freq +
             ___SMMUL(((param_spread + inlet_spread) / (param_LP + param_HP))
                          << 4,
                      i << 26),
         f[i]);
  MTOF(
      -inlet_BW - param_BW + param_freq + inlet_freq -
          ___SMMUL(((param_spread + inlet_spread) / (param_LP + param_HP)) << 4,
                   i << 26),
      g[i]);
}

Audio Rate

int32_t input = inlet_in;

volsat = ___SMMUL(vola << 2, (inlet_res + param_res) << 2);

int dir = volsat > 0 ? 1 : -1;
int32_t in = volsat > 0 ? vola : -volsat;
int32_t gian = ___SMMUL(param_gain << 3, param_gain << 2);
float32_t gain = ___SMMUL((gian + (1 << 17)) << 2, in << 3);
gain = 1 + gain / (1 << 19);
volres = inlet_in + ((param_max) - ((param_max)-in) / gain) * dir;

for (i = 1; i <= (param_LP + param_HP); i++) {
  if (i <= param_LP) {
    if (i == 1) {
      val[i] = ___SMMLA((volres - val[i]) << 1, f[i], val[i]);
    }
    if (i >= 2) {
      val[i] = ___SMMLA((val[i - 1] - val[i]) << 1, f[i], val[i]);
    }
    vil[i] = val[i];
  }

  if (i > param_LP) {
    if (i == 1) {
      val[i] = ___SMMLA((volres - val[i]) << 1, g[i], val[i]);
      vil[i] = volres - val[i];
    } else {
      val[i] = ___SMMLA((val[i - 1] - val[i]) << 1, g[i], val[i]);
      vil[i] = val[i - 1] - val[i];
    }
  }
}

if ((param_LP + param_HP) > 0) {
  outlet_out = vil[param_LP + param_HP];
}
if ((param_LP + param_HP) < 1) {
  outlet_out = inlet_in;
}

int resread =
    param_feed >= (param_LP + param_HP) ? (param_LP + param_HP) : param_feed;

if (resread < param_LP) {
  if (resread > 1) {
    resonance = val[resread] - vil[(resread)-1];
  }
  if (resread == 1) {
    resonance = -inlet_in + val[resread];
  }
}

if (resread >= param_LP) {
  if (resread > 1) {
    resonance = val[resread];
  }
  if (resread == 1) {
    resonance = val[resread];
  }
}

vola = vola + ((-resonance - vola) >> 1);