static void
setup_peak_filter (GstIirEqualizer * equ, GstIirEqualizerBand * band)
{
g_return_if_fail (GST_AUDIO_FILTER (equ)->format.rate);
{
gdouble gain, omega, bw;
gdouble alpha, alpha1, alpha2, b0;
gain = arg_to_scale (band->gain);
omega = calculate_omega (band->freq, GST_AUDIO_FILTER (equ)->format.rate);
bw = calculate_bw (band, GST_AUDIO_FILTER (equ)->format.rate);
if (bw == 0.0)
goto out;
alpha = tan (bw / 2.0);
alpha1 = alpha * gain;
alpha2 = alpha / gain;
b0 = (1.0 + alpha2);
band->a0 = (1.0 + alpha1) / b0;
band->a1 = (-2.0 * cos (omega)) / b0;
band->a2 = (1.0 - alpha1) / b0;
band->b1 = (2.0 * cos (omega)) / b0;
band->b2 = -(1.0 - alpha2) / b0;
out:
GST_INFO
("gain = %5.1f, width= %7.2f, freq = %7.2f, a0 = %7.5g, a1 = %7.5g, a2=%7.5g b1 = %7.5g, b2 = %7.5g",
band->gain, band->width, band->freq, band->a0, band->a1, band->a2,
band->b1, band->b2);
}
}
static void
setup_high_shelf_filter (GstIirEqualizer * equ, GstIirEqualizerBand * band)
{
gint rate = GST_AUDIO_FILTER_RATE (equ);
g_return_if_fail (rate);
{
gdouble gain, omega, bw;
gdouble alpha, delta, b0;
gdouble egp, egm;
gain = arg_to_scale (band->gain);
omega = calculate_omega (band->freq, rate);
bw = calculate_bw (band, rate);
if (bw == 0.0)
goto out;
egm = gain - 1.0;
egp = gain + 1.0;
alpha = tan (bw / 2.0);
delta = 2.0 * sqrt (gain) * alpha;
b0 = egp - egm * cos (omega) + delta;
band->a0 = ((egp + egm * cos (omega) + delta) * gain) / b0;
band->a1 = ((egm + egp * cos (omega)) * -2.0 * gain) / b0;
band->a2 = ((egp + egm * cos (omega) - delta) * gain) / b0;
band->b1 = ((egm - egp * cos (omega)) * -2.0) / b0;
band->b2 = -((egp - egm * cos (omega) - delta)) / b0;
out:
GST_INFO
("gain = %5.1f, width= %7.2f, freq = %7.2f, a0 = %7.5g, a1 = %7.5g, a2=%7.5g b1 = %7.5g, b2 = %7.5g",
band->gain, band->width, band->freq, band->a0, band->a1, band->a2,
band->b1, band->b2);
}
}
/* Filter taken from
*
* The Equivalence of Various Methods of Computing
* Biquad Coefficients for Audio Parametric Equalizers
*
* by Robert Bristow-Johnson
*
* http://www.aes.org/e-lib/browse.cfm?elib=6326
* http://www.musicdsp.org/files/EQ-Coefficients.pdf
*
* The bandwidth method that we use here is the preferred
* one from this article transformed from octaves to frequency
* in Hz.
*/
static void
setup_filter (GstIirEqualizer * equ, GstIirEqualizerBand * band)
{
g_return_if_fail (GST_AUDIO_FILTER (equ)->format.rate);
/* FIXME: we need better filters
* - we need shelf-filter for 1st and last band
*/
{
gdouble gain, omega, bw;
gdouble edge_gain, gamma;
gdouble alpha, beta;
gain = arg_to_scale (band->gain);
if (band->freq / GST_AUDIO_FILTER (equ)->format.rate > 0.5)
omega = M_PI;
else if (band->freq < 0.0)
omega = 0.0;
else
omega = 2.0 * M_PI * (band->freq / GST_AUDIO_FILTER (equ)->format.rate);
if (band->width / GST_AUDIO_FILTER (equ)->format.rate >= 0.5) {
/* If bandwidth == 0.5 the calculation below fails as tan(M_PI/2)
* is undefined. So set the bandwidth to a slightly smaller value.
*/
bw = M_PI - 0.00000001;
} else if (band->width <= 0.0) {
/* If bandwidth == 0 this band won't change anything so set
* the coefficients accordingly. The coefficient calculation
* below would create coefficients that for some reason amplify
* the band.
*/
band->a0 = 1.0;
band->a1 = 0.0;
band->a2 = 0.0;
band->b1 = 0.0;
band->b2 = 0.0;
gain = 1.0;
goto out;
} else {
bw = 2.0 * M_PI * (band->width / GST_AUDIO_FILTER (equ)->format.rate);
}
edge_gain = sqrt (gain);
gamma = tan (bw / 2.0);
alpha = gamma * edge_gain;
beta = gamma / edge_gain;
band->a0 = (1.0 + alpha) / (1.0 + beta);
band->a1 = (-2.0 * cos (omega)) / (1.0 + beta);
band->a2 = (1.0 - alpha) / (1.0 + beta);
band->b1 = (2.0 * cos (omega)) / (1.0 + beta);
band->b2 = -(1.0 - beta) / (1.0 + beta);
out:
GST_INFO
("gain = %5.1f, width= %7.2f, freq = %7.2f, a0 = %7.5g, a1 = %7.5g, a2=%7.5g b1 = %7.5g, b2 = %7.5g",
band->gain, band->width, band->freq, band->a0, band->a1, band->a2,
band->b1, band->b2);
}
}
