Akso - Audio DSP Platform

BPstack

$\text{[math]}$

Up 16x stackable BP-filter -pitch controls the center frequency of all filters -Pspread spreads the frequencies of all the filters over the entire spectrum -reso sets the resonance amount -rate sets the frequency modulation rate -spread sets adds a phase-offset of each next filter-LFO -depth sets the modulation depth -stack sets the amount of filters that will be stacked (max=16)

Author: Remco van der Most

License: BSD

Github: sss/filter/BPstack.axo

Inlets

frac32buffer filter input

frac32 pitch1

frac32 Pspread

frac32 reso1

frac32 rate

frac32 spread

frac32 depth

frac32 phase

Outlets

frac32buffer filter output

Parameters

frac32.u.map.filterq reso1

int32.hradio mode

int32 stack

frac32.s.map.pitch pitch1

frac32.s.map Pspread

frac32.s.map rate

frac32.s.map spread

frac32.s.map depth

Declaration

int32_t low[16];
int32_t band[16];
int32_t OUT[16];
int32_t freq[16];
int32_t Damp[16];
int32_t IN[17];
int32_t LFO;
int32_t sym;
int i;
int mode;
int32_t config(int32_t pitch, int32_t reso, int Inst) {
  int32_t damp = (0x80 << 24) - (reso << 4);
  damp = ___SMMUL(damp, damp);
  Damp[Inst] = damp;
  int32_t alpha;
  MTOFEXTENDED(pitch, alpha);
  SINE2TINTERP(alpha, freq[Inst]);
}

int32_t SVF(int32_t in1, int32_t Freq, int32_t damp, int32_t Inst,
            int32_t stack) {
  if (mode > 1) {
    in1 = IN[0];
  }
  int32_t notch = in1 - __SSAT((___SMMUL(damp, band[Inst]) << 1), 27);
  low[Inst] = low[Inst] + __SSAT((___SMMUL(Freq, band[Inst]) << 1), 27);
  int32_t high = notch - low[Inst];
  band[Inst] = (___SMMUL(Freq, high) << 1) + __SSAT(band[Inst], 27);
  if (mode == 0) {
    IN[Inst + 1] = in1 - band[Inst];
  }
  if (mode == 1) {
    IN[Inst + 1] = in1 + band[Inst] / 5 * 3;
  }
  if (mode == 2) {
    IN[Inst + 1] = in1 - band[Inst];
  }
  if (mode == 3) {
    IN[Inst + 1] = in1 + band[Inst] / 5 * 3;
  }
}

Init

for (i = 0; i < 2; i++) {
  low[i] = 0;
  band[i] = 0;
}

Control Rate

int32_t rate;
MTOFEXTENDED(param_rate + inlet_rate, rate)

mode = param_mode;
LFO += rate >> 6;
for (i = 0; i < param_stack; i++) {
  int32_t lfo =
      LFO + inlet_phase +
          (((param_spread + inlet_spread) << 4) / (param_stack)*i << 2) >>
      4;
  lfo = lfo > 0 ? lfo : -lfo;
  lfo = ___SMMUL((param_depth + inlet_depth) << 3, lfo << 2);
  int32_t PITCH = inlet_pitch1 + param_pitch1 + lfo +
                  (((param_Pspread + inlet_Pspread)) / (param_stack)*i);
  PITCH = PITCH > (1 << 27) ? (1 << 28) - PITCH : PITCH;
  PITCH = PITCH < (-1 << 27) ? (-1 << 28) + PITCH : PITCH;
  config(PITCH, __USAT(param_reso1 + inlet_reso1, 27), i);
}

Audio Rate

IN[0] = inlet_in1;
for (i = 0; i < param_stack; i++) {
  SVF(IN[i], freq[i], Damp[i], i, param_stack);
}
sym = IN[param_stack];
if (mode > 1) {
  sym = 0;
  for (i = 0; i < param_stack; i++) {
    sym += IN[i + 1];
  }
}
outlet_out = (sym >> 1);