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#include "Biquad.h"
#include <assert.h>
#include <math.h>
Biquad::Biquad()
: sampleRate(44100)
, _f0(1000)
{
_z_eq_b[0] = 1;
_z_eq_b[1] = 0;
_z_eq_b[2] = 0;
_z_eq_a[0] = 1;
_z_eq_a[1] = 0;
_z_eq_a[2] = 0;
clear_buffers();
_s_eq_a[0] = 1;
_s_eq_a[1] = 2;
_s_eq_a[2] = 1;
_s_eq_b[0] = _s_eq_a[0];
_s_eq_b[1] = _s_eq_a[1];
_s_eq_b[2] = _s_eq_a[2];
}
#define M_PI 3.14159265358979323846
// warp to the z-plane
void Biquad::transform_s_to_z()
{
// s to z bilinear transform
const double inv_k = tan(_f0 * M_PI / sampleRate);
const double k = 1 / inv_k;
const double kk = k*k;
const double b1k = _s_eq_b[1] * k;
const double b2kk = _s_eq_b[2] * kk;
const double b2kk_plus_b0 = b2kk + _s_eq_b[0];
const double b0z = b2kk_plus_b0 + b1k;
const double b2z = b2kk_plus_b0 - b1k;
const double b1z = 2 * (_s_eq_b[0] - b2kk);
const double a1k = _s_eq_a[1] * k;
const double a2kk = _s_eq_a[2] * kk;
const double a2kk_plus_a0 = a2kk + _s_eq_a[0];
const double a0z = a2kk_plus_a0 + a1k;
const double a2z = a2kk_plus_a0 - a1k;
const double a1z = 2 * (_s_eq_a[0] - a2kk);
// IIR coefficients
const double mult = 1 / a0z;
_z_eq_b[0] = float(b0z * mult);
_z_eq_b[1] = float(b1z * mult);
_z_eq_b[2] = float(b2z * mult);
_z_eq_a[0] = 1;
_z_eq_a[1] = float(a1z * mult);
_z_eq_a[2] = float(a2z * mult);
}
void Biquad::process_block(float *dest_ptr, const float *src_ptr, long nbr_spl)
{
assert(nbr_spl >= 0);
if (nbr_spl == 0)
{
return;
}
// If we're not on a pair boudary, we process a single sample.
if (_mem_pos != 0)
{
*dest_ptr++ = (float)process_sample(*src_ptr++);
nbr_spl--;
}
if (nbr_spl == 0)
{
return;
}
long half_nbr_spl = nbr_spl >> 1;
long index = 0;
if (half_nbr_spl > 0)
{
double mem_x[2];
double mem_y[2];
mem_x[0] = xn[0];
mem_x[1] = xn[1];
mem_y[0] = yn[0];
mem_y[1] = yn[1];
do
{
float x = src_ptr[index];
mem_y[1] = _z_eq_b[0] * x
+ (_z_eq_b[1] * mem_x[0]
+ _z_eq_b[2] * mem_x[1])
- (_z_eq_a[1] * mem_y[0]
+ _z_eq_a[2] * mem_y[1]);
mem_x[1] = x;
dest_ptr[index] = (float)mem_y[1];
x = src_ptr[index + 1];
mem_y[0] = _z_eq_b[0] * x
+ (_z_eq_b[1] * mem_x[1]
+ _z_eq_b[2] * mem_x[0])
- (_z_eq_a[1] * mem_y[1]
+ _z_eq_a[2] * mem_y[0]);
mem_x[0] = x;
dest_ptr[index + 1] = (float)mem_y[0];
index += 2;
-- half_nbr_spl;
}
while (half_nbr_spl > 0);
xn[0] = mem_x[0];
xn[1] = mem_x[1];
yn[0] = mem_y[0];
yn[1] = mem_y[1];
}
// If number of samples was odd, there is one more to process.
if ((nbr_spl & 1) > 0)
{
dest_ptr[index] = (float)process_sample(src_ptr[index]);
}
}
void Biquad::clear_buffers()
{
xn[0] = 0;
xn[1] = 0;
yn[0] = 0;
yn[1] = 0;
_mem_pos = 0;
}
double Biquad::process_sample(double x)
{
const int alt_pos = 1 - _mem_pos;
const double y = _z_eq_b[0] * x
+ (_z_eq_b[1] * xn[_mem_pos]
+ _z_eq_b[2] * xn[alt_pos])
- (_z_eq_a[1] * yn[_mem_pos]
+ _z_eq_a[2] * yn[alt_pos]);
xn[alt_pos] = x;
yn[alt_pos] = y;
_mem_pos = alt_pos;
return (y);
}
void Biquad::copy_filter(const Biquad &other)
{
_z_eq_b[0] = other._z_eq_b[0];
_z_eq_b[1] = other._z_eq_b[1];
_z_eq_b[2] = other._z_eq_b[2];
_z_eq_a[1] = other._z_eq_a[1];
_z_eq_a[2] = other._z_eq_a[2];
sampleRate = other.sampleRate;
_f0 = other._f0;
set_s_eq(other._s_eq_b, other._s_eq_a);
}
void Biquad::SetSampleRate(double fs)
{
assert(fs > 0);
sampleRate = fs;
transform_s_to_z();
}
void Biquad::set_freq(double f0)
{
assert(f0 > 0);
_f0 = f0;
}
void Biquad::set_s_eq(const double b[3], const double a[3])
{
assert(a != 0);
assert(a[2] != 0);
assert(b != 0);
_s_eq_b[0] = float(b[0]);
_s_eq_b[1] = float(b[1]);
_s_eq_b[2] = float(b[2]);
_s_eq_a[0] = float(a[0]);
_s_eq_a[1] = float(a[1]);
_s_eq_a[2] = float(a[2]);
}
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