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equalizer: use shelfing filters for first and last band

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Refactor the filter setup. Add two new filters with shelf characteristics for
first and last band. Change gain calculation as recommended in the quoted
document (no qrt needed). Rename variables to match the formulas in the
document.
This commit is contained in:
Stefan Kost 2009-10-07 00:33:49 +03:00
parent 15c6175044
commit 27ea0b076a
1 changed files with 146 additions and 56 deletions
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172
gst/equalizer/gstiirequalizer.c
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@ -121,10 +121,6 @@ struct _GstIirEqualizerBandClass
static GType gst_iir_equalizer_band_get_type (void); static GType gst_iir_equalizer_band_get_type (void);
static void setup_filter (GstIirEqualizer * equ, GstIirEqualizerBand * band);
static void set_passthrough (GstIirEqualizer * equ);
static void static void
gst_iir_equalizer_band_set_property (GObject * object, guint prop_id, gst_iir_equalizer_band_set_property (GObject * object, guint prop_id,
const GValue * value, GParamSpec * pspec) const GValue * value, GParamSpec * pspec)
@ -357,12 +353,6 @@ gst_iir_equalizer_finalize (GObject * object)
G_OBJECT_CLASS (parent_class)->finalize (object); G_OBJECT_CLASS (parent_class)->finalize (object);
} }
static inline gdouble
arg_to_scale (gdouble arg)
{
return (pow (10.0, arg / 20.0));
}
/* Filter taken from /* Filter taken from
* *
* The Equivalence of Various Methods of Computing * The Equivalence of Various Methods of Computing
@ -372,34 +362,39 @@ arg_to_scale (gdouble arg)
* *
* http://www.aes.org/e-lib/browse.cfm?elib=6326 * http://www.aes.org/e-lib/browse.cfm?elib=6326
* http://www.musicdsp.org/files/EQ-Coefficients.pdf * http://www.musicdsp.org/files/EQ-Coefficients.pdf
* http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
* *
* The bandwidth method that we use here is the preferred * The bandwidth method that we use here is the preferred
* one from this article transformed from octaves to frequency * one from this article transformed from octaves to frequency
* in Hz. * in Hz.
*/ */
static void static inline gdouble
setup_filter (GstIirEqualizer * equ, GstIirEqualizerBand * band) arg_to_scale (gdouble arg)
{ {
g_return_if_fail (GST_AUDIO_FILTER (equ)->format.rate); return (pow (10.0, arg / 40.0));
}
/* FIXME: we need better filters static gdouble
* - we need shelf-filter for 1st and last band calculate_omega (gdouble freq, gint rate)
*/ {
{ gdouble omega;
gdouble gain, omega, bw;
gdouble edge_gain, gamma;
gdouble alpha, beta;
gain = arg_to_scale (band->gain); if (freq / rate >= 0.5)
if (band->freq / GST_AUDIO_FILTER (equ)->format.rate >= 0.5)
omega = M_PI; omega = M_PI;
else if (band->freq <= 0.0) else if (freq <= 0.0)
omega = 0.0; omega = 0.0;
else else
omega = 2.0 * M_PI * (band->freq / GST_AUDIO_FILTER (equ)->format.rate); omega = 2.0 * M_PI * (freq / rate);
if (band->width / GST_AUDIO_FILTER (equ)->format.rate >= 0.5) { return omega;
}
static gdouble
calculate_bw (GstIirEqualizerBand * band, gint rate)
{
gdouble bw = 0.0;
if (band->width / rate >= 0.5) {
/* If bandwidth == 0.5 the calculation below fails as tan(M_PI/2) /* If bandwidth == 0.5 the calculation below fails as tan(M_PI/2)
* is undefined. So set the bandwidth to a slightly smaller value. * is undefined. So set the bandwidth to a slightly smaller value.
*/ */
@ -415,23 +410,115 @@ setup_filter (GstIirEqualizer * equ, GstIirEqualizerBand * band)
band->a2 = 0.0; band->a2 = 0.0;
band->b1 = 0.0; band->b1 = 0.0;
band->b2 = 0.0; band->b2 = 0.0;
gain = 1.0;
goto out;
} else { } else {
bw = 2.0 * M_PI * (band->width / GST_AUDIO_FILTER (equ)->format.rate); bw = 2.0 * M_PI * (band->width / rate);
} }
return bw;
}
edge_gain = sqrt (gain); static void
gamma = tan (bw / 2.0); setup_peak_filter (GstIirEqualizer * equ, GstIirEqualizerBand * band)
{
g_return_if_fail (GST_AUDIO_FILTER (equ)->format.rate);
alpha = gamma * edge_gain; {
beta = gamma / edge_gain; 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_low_shelf_filter (GstIirEqualizer * equ, GstIirEqualizerBand * band)
{
g_return_if_fail (GST_AUDIO_FILTER (equ)->format.rate);
{
gdouble gain, omega, bw;
gdouble alpha, delta, b0;
gdouble egp, egm;
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;
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);
}
}
static void
setup_high_shelf_filter (GstIirEqualizer * equ, GstIirEqualizerBand * band)
{
g_return_if_fail (GST_AUDIO_FILTER (equ)->format.rate);
{
gdouble gain, omega, bw;
gdouble alpha, delta, b0;
gdouble egp, egm;
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;
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;
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: out:
GST_INFO GST_INFO
@ -459,11 +546,14 @@ set_passthrough (GstIirEqualizer * equ)
static void static void
update_coefficients (GstIirEqualizer * equ) update_coefficients (GstIirEqualizer * equ)
{ {
gint i; gint i, n = equ->freq_band_count;
for (i = 0; i < equ->freq_band_count; i++) { setup_low_shelf_filter (equ, equ->bands[0]);
setup_filter (equ, equ->bands[i]); for (i = 1; i < n - 1; i++) {
setup_peak_filter (equ, equ->bands[i]);
} }
setup_high_shelf_filter (equ, equ->bands[n - 1]);
equ->need_new_coefficients = FALSE; equ->need_new_coefficients = FALSE;
} }