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/*
Eq.h
Copyright 2004 Tim Goetze <tim@quitte.de>
http://quitte.de/dsp/
equalizer circuit using recursive filtering.
based on a motorola paper implementing a similar circuit on a DSP56001.
*/
/*
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA or point your web browser to http://www.gnu.org.
*/
#ifndef _DSP_EQ_H_
#define _DSP_EQ_H_
namespace DSP {
/* a single bandpass as used by the Eq, expressed as a biquad. like all
* band-pass filters i know, the filter works with a FIR coefficient of 0
* for x[-1], so a generic biquad isn't the optimum implementation.
*/
class BP
{
public:
template <class T>
BP (double fc, double Q, T * ca, T * cb)
{
double theta = 2 * fc * M_PI;
double
b = (Q - theta * .5) / (2 * Q + theta),
a = (.5 - b) / 2,
c = (.5 + b) * cos (theta);
ca[0] = 2 * a;
ca[1] = 0;
ca[2] = -2 * a;
cb[0] = 0;
cb[1] = 2 * c;
cb[2] = -2 * b;
}
};
/* BANDS must be a multiple of 4 to enable the use of SSE instructions.
* however, the current SSE-enabled process() method fails to compile if
* -funroll-loops is passed to gcc.
*/
template <int USE_BANDS, int BANDS>
class Eq
{
public:
/* over-size state buffer to allow alignment */
float state [BANDS * 8 + 4 + 4];
/* recursion coefficients, 3 per band */
float * a, * b, * c;
/* past outputs, 2 per band */
float * y;
/* current gain and recursion factor, each 1 per band = 2 */
float * gain, * gf;
/* aligned storage for output summation */
float * temp;
/* aligned storage for constants */
float * two;
/* input history */
float x[2];
/* history index */
int h;
Eq()
{
/* take care of 128-bit alignment */
long s = (long) (char *) state;
s &= 0xF;
if (s)
s = 16 - s;
/* assign coefficients */
a = (float *) (((char *) state) + s);
b = a + BANDS;
c = a + 2 * BANDS;
/* output history (input is common to all bands) */
y = a + 3 * BANDS;
gain = a + 5 * BANDS;
gf = a + 6 * BANDS;
temp = a + 7 * BANDS;
two = temp + 4;
two[0] = two[1] = two[2] = two[3] = 2;
h = 0;
}
void reset()
{
for (int i = 0; i < 2 * BANDS; ++i)
y[i] = 0;
for (int i = 0; i < 2; ++i)
x[i] = 0;
}
void init (double fs, double Q)
{
double f = 31.25;
int i = 0;
for (i = 0; i < USE_BANDS && f < fs / 2; ++i, f *= 2)
init_band (i, 2 * f * M_PI / fs, Q);
for ( ; i < BANDS; ++i)
zero_band (i);
reset();
}
void init_band (int i, double theta, double Q)
{
b[i] = (Q - theta * .5) / (2 * Q + theta);
a[i] = (.5 - b[i]) / 2;
c[i] = (.5 + b[i]) * cos (theta);
gain[i] = 1;
gf[i] = 1;
}
void zero_band (int i)
{
a[i] = b[i] = c[i] = 0;
}
/* per-band recursion:
* y = 2 * (a * (x - x[-2]) + c * y[-1] - b * y[-2])
*/
d_sample process (d_sample s)
{
int z1 = h, z2 = h ^ 1;
float * y1 = y + z1 * BANDS;
float * y2 = y + z2 * BANDS;
d_sample x_x2 = s - x[z2];
d_sample r = 0;
for (int i = 0; i < USE_BANDS; ++i)
{
y2[i] = 2 * (a[i] * x_x2 + c[i] * y1[i] - b[i] * y2[i]);
r += gain[i] * y2[i];
gain[i] *= gf[i];
}
x[z2] = s;
h = z2;
return r;
}
};
} /* namespace DSP */
#endif /* _DSP_EQ_H_ */
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