Akso - Audio DSP Platform

formantFilter

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Formant filter Connect the corresponding outputs on the formant controller to the inputs of the filter. Feed a signal into the "in" input to induce the formants on (normally a saw is used, but you can use any oscillator!) Two BP filter modes (I like 2 the most with resonance set to around 20). The resonance knob adds extra resonance to the normal settings (so 0 would be the setting set by the formant controller, but I like the resonance to be a bit higher). If you have high volume problems, lower the volume of the input sound or add the "fatbasterd" module to soft-clip it.

Author: Remco van der Most

License: BSD

Github: sss/filter/formantFilter.axo

Inlets

frac32buffer in

frac32 frq1

frac32 frq2

frac32 frq3

frac32 frq4

frac32 frq5

frac32 bw1

frac32 bw2

frac32 bw3

frac32 bw4

frac32 bw5

frac32 gain1

frac32 gain2

frac32 gain3

frac32 gain4

frac32 gain5

frac32.positive resonance

Outlets

frac32buffer out

Parameters

int32.hradio mode

frac32.u.map resonance

Declaration

float32_t f0[5];
float32_t dBgain[5];
float32_t BW[5];
float32_t A[5];
float32_t w0[5];
float32_t alpha[5];
float32_t b0[5];
float32_t b1[5];
float32_t b2[5];
float32_t a0[5];
float32_t a1[5];
float32_t a2[5];
float32_t wcos0[5];
int32_t sum[5];
int32_t bprev1;
int32_t bprev2;
int32_t anext1[5];
int32_t anext2[5];
float32_t ln;
int32_t sam;
float32_t E;
int i;
int j;
float32_t e;
int32_t sim;
int shift;

Init

bprev1 = 0;
bprev2 = 0;
for (i = 0; i < 5; i++) {
  anext1[i] = 0;
  anext2[i] = 0;
}

ln = 0.693147180559945309417232121458;
e = 2.718281828459045235360287471352662497757247093;

Control Rate

float32_t Fs = 48000;
float32_t res = (float)(param_resonance + param_resonance);
float32_t pi = 3.141592653589793238462643383279502884;

f0[0] = ((float)inlet_frq1) / (1 << 16);
f0[1] = ((float)inlet_frq2) / (1 << 16);
f0[2] = ((float)inlet_frq3) / (1 << 16);
f0[3] = ((float)inlet_frq4) / (1 << 16);
f0[4] = ((float)inlet_frq5) / (1 << 16);
dBgain[0] = ((float)inlet_gain1) / (1 << 21);
dBgain[1] = ((float)inlet_gain2) / (1 << 21);
dBgain[2] = ((float)inlet_gain3) / (1 << 21);
dBgain[3] = ((float)inlet_gain4) / (1 << 21);
dBgain[4] = ((float)inlet_gain5) / (1 << 21);
BW[0] = ((float)inlet_bw1) / (1 << 16);
BW[1] = ((float)inlet_bw2) / (1 << 16);
BW[2] = ((float)inlet_bw3) / (1 << 16);
BW[3] = ((float)inlet_bw4) / (1 << 16);
BW[4] = ((float)inlet_bw5) / (1 << 16);

for (i = 0; i < 5; i++) {
  dBgain[i] = dBgain[i] < -20 ? -20 : dBgain[i];
  A[i] = (powf(10, dBgain[i]) / 40);
  w0[i] = 2 * pi * f0[i] / Fs;
  wcos0[i] = cosf(w0[i]);

  switch (param_mode > 0 ? param_mode : 0) {
  case 0:
    alpha[i] = (sinf(w0[i])) / (((res / (1 << 24)) + 2) * BW[i] / f0[i]);
    a0[i] = 1 + alpha[i];
    b0[i] = sinf(w0[i]) / 2 / a0[i];
    b1[i] = 0;
    b2[i] = -sinf(w0[i]) / 2 / a0[i];
    a1[i] = -2 * wcos0[i] / a0[i];
    a2[i] = 1 - alpha[i] / a0[i];
    dBgain[i] = powf(0.5, -dBgain[i] / 6);
    shift = 0;
    break;
  case 1:
    alpha[i] = (sinf(w0[i])) / (((res / (1 << 20)) + 2) * BW[i] / f0[i]);
    a0[i] = 1 + alpha[i];
    b0[i] = alpha[i] / a0[i];
    b1[i] = 0;
    b2[i] = -alpha[i] / a0[i];
    a1[i] = -2 * wcos0[i] / a0[i];
    a2[i] = 1 - alpha[i] / a0[i];
    dBgain[i] = powf(0.5, -dBgain[i] / 6);
    shift = 0;
    break;
  }
}

Audio Rate

sam = 0;
int32_t in = inlet_in >> 1;
bprev2 = bprev1;
bprev1 = in;
for (j = 0; j < 5; j++) {
  sum[j] = in * b0[j] + bprev2 * b2[j] - anext1[j] * a1[j] - anext2[j] * a2[j];
  anext2[j] = anext1[j];
  anext1[j] = sum[j];

  sim += (___SMMUL(sum[j], (1 << 31) - (res)) * dBgain[i]);
}
outlet_out = sim >> 5;