/*
* GStreamer
* Copyright (C) 2007-2009 Sebastian Dröge <sebastian.droege@collabora.co.uk>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library 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
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/*
* Chebyshev type 1 filter design based on
* "The Scientist and Engineer's Guide to DSP", Chapter 20.
* http://www.dspguide.com/
*
* For type 2 and Chebyshev filters in general read
* http://en.wikipedia.org/wiki/Chebyshev_filter
*
*/
/**
* SECTION:element-audiocheblimit
*
* Attenuates all frequencies above the cutoff frequency (low-pass) or all frequencies below the
* cutoff frequency (high-pass). The number of poles and the ripple parameter control the rolloff.
*
* This element has the advantage over the windowed sinc lowpass and highpass filter that it is
* much faster and produces almost as good results. It's only disadvantages are the highly
* non-linear phase and the slower rolloff compared to a windowed sinc filter with a large kernel.
*
* For type 1 the ripple parameter specifies how much ripple in dB is allowed in the passband, i.e.
* some frequencies in the passband will be amplified by that value. A higher ripple value will allow
* a faster rolloff.
*
* For type 2 the ripple parameter specifies the stopband attenuation. In the stopband the gain will
* be at most this value. A lower ripple value will allow a faster rolloff.
*
* As a special case, a Chebyshev type 1 filter with no ripple is a Butterworth filter.
* </para>
* <note><para>
* Be warned that a too large number of poles can produce noise. The most poles are possible with
* a cutoff frequency at a quarter of the sampling rate.
* </para></note>
* <para>
* <refsect2>
* <title>Example launch line</title>
* |[
* gst-launch audiotestsrc freq=1500 ! audioconvert ! audiocheblimit mode=low-pass cutoff=1000 poles=4 ! audioconvert ! alsasink
* gst-launch filesrc location="melo1.ogg" ! oggdemux ! vorbisdec ! audioconvert ! audiocheblimit mode=high-pass cutoff=400 ripple=0.2 ! audioconvert ! alsasink
* gst-launch audiotestsrc wave=white-noise ! audioconvert ! audiocheblimit mode=low-pass cutoff=800 type=2 ! audioconvert ! alsasink
* ]|
* </refsect2>
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <gst/gst.h>
#include <gst/base/gstbasetransform.h>
#include <gst/audio/audio.h>
#include <gst/audio/gstaudiofilter.h>
#include <gst/controller/gstcontroller.h>
#include <math.h>
#include "math_compat.h"
#include "audiocheblimit.h"
#define GST_CAT_DEFAULT gst_audio_cheb_limit_debug
GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);
enum
{
PROP_0,
PROP_MODE,
PROP_TYPE,
PROP_CUTOFF,
PROP_RIPPLE,
PROP_POLES
};
#define DEBUG_INIT(bla) \
GST_DEBUG_CATEGORY_INIT (gst_audio_cheb_limit_debug, "audiocheblimit", 0, "audiocheblimit element");
GST_BOILERPLATE_FULL (GstAudioChebLimit,
gst_audio_cheb_limit, GstAudioFXBaseIIRFilter,
GST_TYPE_AUDIO_FX_BASE_IIR_FILTER, DEBUG_INIT);
static void gst_audio_cheb_limit_set_property (GObject * object,
guint prop_id, const GValue * value, GParamSpec * pspec);
static void gst_audio_cheb_limit_get_property (GObject * object,
guint prop_id, GValue * value, GParamSpec * pspec);
static void gst_audio_cheb_limit_finalize (GObject * object);
static gboolean gst_audio_cheb_limit_setup (GstAudioFilter * filter,
GstRingBufferSpec * format);
enum
{
MODE_LOW_PASS = 0,
MODE_HIGH_PASS
};
#define GST_TYPE_AUDIO_CHEBYSHEV_FREQ_LIMIT_MODE (gst_audio_cheb_limit_mode_get_type ())
static GType
gst_audio_cheb_limit_mode_get_type (void)
{
static GType gtype = 0;
if (gtype == 0) {
static const GEnumValue values[] = {
{MODE_LOW_PASS, "Low pass (default)",
"low-pass"},
{MODE_HIGH_PASS, "High pass",
"high-pass"},
{0, NULL, NULL}
};
gtype = g_enum_register_static ("GstAudioChebLimitMode", values);
}
return gtype;
}
/* GObject vmethod implementations */
static void
gst_audio_cheb_limit_base_init (gpointer klass)
{
GstElementClass *element_class = GST_ELEMENT_CLASS (klass);
gst_element_class_set_details_simple (element_class,
"Low pass & high pass filter",
"Filter/Effect/Audio",
"Chebyshev low pass and high pass filter",
"Sebastian Dröge <sebastian.droege@collabora.co.uk>");
}
static void
gst_audio_cheb_limit_class_init (GstAudioChebLimitClass * klass)
{
GObjectClass *gobject_class = (GObjectClass *) klass;
GstAudioFilterClass *filter_class = (GstAudioFilterClass *) klass;
gobject_class->set_property = gst_audio_cheb_limit_set_property;
gobject_class->get_property = gst_audio_cheb_limit_get_property;
gobject_class->finalize = gst_audio_cheb_limit_finalize;
g_object_class_install_property (gobject_class, PROP_MODE,
g_param_spec_enum ("mode", "Mode",
"Low pass or high pass mode",
GST_TYPE_AUDIO_CHEBYSHEV_FREQ_LIMIT_MODE, MODE_LOW_PASS,
G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
g_object_class_install_property (gobject_class, PROP_TYPE,
g_param_spec_int ("type", "Type", "Type of the chebychev filter", 1, 2, 1,
G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
/* FIXME: Don't use the complete possible range but restrict the upper boundary
* so automatically generated UIs can use a slider without */
g_object_class_install_property (gobject_class, PROP_CUTOFF,
g_param_spec_float ("cutoff", "Cutoff", "Cut off frequency (Hz)", 0.0,
100000.0, 0.0,
G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
g_object_class_install_property (gobject_class, PROP_RIPPLE,
g_param_spec_float ("ripple", "Ripple", "Amount of ripple (dB)", 0.0,
200.0, 0.25,
G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
/* FIXME: What to do about this upper boundary? With a cutoff frequency of
* rate/4 32 poles are completely possible, with a cutoff frequency very low
* or very high 16 poles already produces only noise */
g_object_class_install_property (gobject_class, PROP_POLES,
g_param_spec_int ("poles", "Poles",
"Number of poles to use, will be rounded up to the next even number",
2, 32, 4,
G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
filter_class->setup = GST_DEBUG_FUNCPTR (gst_audio_cheb_limit_setup);
}
static void
gst_audio_cheb_limit_init (GstAudioChebLimit * filter,
GstAudioChebLimitClass * klass)
{
filter->cutoff = 0.0;
filter->mode = MODE_LOW_PASS;
filter->type = 1;
filter->poles = 4;
filter->ripple = 0.25;
filter->lock = g_mutex_new ();
}
static void
generate_biquad_coefficients (GstAudioChebLimit * filter,
gint p, gdouble * a0, gdouble * a1, gdouble * a2,
gdouble * b1, gdouble * b2)
{
gint np = filter->poles;
gdouble ripple = filter->ripple;
/* pole location in s-plane */
gdouble rp, ip;
/* zero location in s-plane */
gdouble iz = 0.0;
/* transfer function coefficients for the z-plane */
gdouble x0, x1, x2, y1, y2;
gint type = filter->type;
/* Calculate pole location for lowpass at frequency 1 */
{
gdouble angle = (M_PI / 2.0) * (2.0 * p - 1) / np;
rp = -sin (angle);
ip = cos (angle);
}
/* If we allow ripple, move the pole from the unit
* circle to an ellipse and keep cutoff at frequency 1 */
if (ripple > 0 && type == 1) {
gdouble es, vx;
es = sqrt (pow (10.0, ripple / 10.0) - 1.0);
vx = (1.0 / np) * asinh (1.0 / es);
rp = rp * sinh (vx);
ip = ip * cosh (vx);
} else if (type == 2) {
gdouble es, vx;
es = sqrt (pow (10.0, ripple / 10.0) - 1.0);
vx = (1.0 / np) * asinh (es);
rp = rp * sinh (vx);
ip = ip * cosh (vx);
}
/* Calculate inverse of the pole location to convert from
* type I to type II */
if (type == 2) {
gdouble mag2 = rp * rp + ip * ip;
rp /= mag2;
ip /= mag2;
}
/* Calculate zero location for frequency 1 on the
* unit circle for type 2 */
if (type == 2) {
gdouble angle = M_PI / (np * 2.0) + ((p - 1) * M_PI) / (np);
gdouble mag2;
iz = cos (angle);
mag2 = iz * iz;
iz /= mag2;
}
/* Convert from s-domain to z-domain by
* using the bilinear Z-transform, i.e.
* substitute s by (2/t)*((z-1)/(z+1))
* with t = 2 * tan(0.5).
*/
if (type == 1) {
gdouble t, m, d;
t = 2.0 * tan (0.5);
m = rp * rp + ip * ip;
d = 4.0 - 4.0 * rp * t + m * t * t;
x0 = (t * t) / d;
x1 = 2.0 * x0;
x2 = x0;
y1 = (8.0 - 2.0 * m * t * t) / d;
y2 = (-4.0 - 4.0 * rp * t - m * t * t) / d;
} else {
gdouble t, m, d;
t = 2.0 * tan (0.5);
m = rp * rp + ip * ip;
d = 4.0 - 4.0 * rp * t + m * t * t;
x0 = (t * t * iz * iz + 4.0) / d;
x1 = (-8.0 + 2.0 * iz * iz * t * t) / d;
x2 = x0;
y1 = (8.0 - 2.0 * m * t * t) / d;
y2 = (-4.0 - 4.0 * rp * t - m * t * t) / d;
}
/* Convert from lowpass at frequency 1 to either lowpass
* or highpass.
*
* For lowpass substitute z^(-1) with:
* -1
* z - k
* ------------
* -1
* 1 - k * z
*
* k = sin((1-w)/2) / sin((1+w)/2)
*
* For highpass substitute z^(-1) with:
*
* -1
* -z - k
* ------------
* -1
* 1 + k * z
*
* k = -cos((1+w)/2) / cos((1-w)/2)
*
*/
{
gdouble k, d;
gdouble omega =
2.0 * M_PI * (filter->cutoff / GST_AUDIO_FILTER (filter)->format.rate);
if (filter->mode == MODE_LOW_PASS)
k = sin ((1.0 - omega) / 2.0) / sin ((1.0 + omega) / 2.0);
else
k = -cos ((omega + 1.0) / 2.0) / cos ((omega - 1.0) / 2.0);
d = 1.0 + y1 * k - y2 * k * k;
*a0 = (x0 + k * (-x1 + k * x2)) / d;
*a1 = (x1 + k * k * x1 - 2.0 * k * (x0 + x2)) / d;
*a2 = (x0 * k * k - x1 * k + x2) / d;
*b1 = (2.0 * k + y1 + y1 * k * k - 2.0 * y2 * k) / d;
*b2 = (-k * k - y1 * k + y2) / d;
if (filter->mode == MODE_HIGH_PASS) {
*a1 = -*a1;
*b1 = -*b1;
}
}
}
static void
generate_coefficients (GstAudioChebLimit * filter)
{
if (GST_AUDIO_FILTER (filter)->format.rate == 0) {
gdouble *a = g_new0 (gdouble, 1);
a[0] = 1.0;
gst_audio_fx_base_iir_filter_set_coefficients (GST_AUDIO_FX_BASE_IIR_FILTER
(filter), a, 1, NULL, 0);
GST_LOG_OBJECT (filter, "rate was not set yet");
return;
}
if (filter->cutoff >= GST_AUDIO_FILTER (filter)->format.rate / 2.0) {
gdouble *a = g_new0 (gdouble, 1);
a[0] = (filter->mode == MODE_LOW_PASS) ? 1.0 : 0.0;
gst_audio_fx_base_iir_filter_set_coefficients (GST_AUDIO_FX_BASE_IIR_FILTER
(filter), a, 1, NULL, 0);
GST_LOG_OBJECT (filter, "cutoff was higher than nyquist frequency");
return;
} else if (filter->cutoff <= 0.0) {
gdouble *a = g_new0 (gdouble, 1);
a[0] = (filter->mode == MODE_LOW_PASS) ? 0.0 : 1.0;
gst_audio_fx_base_iir_filter_set_coefficients (GST_AUDIO_FX_BASE_IIR_FILTER
(filter), a, 1, NULL, 0);
GST_LOG_OBJECT (filter, "cutoff is lower than zero");
return;
}
/* Calculate coefficients for the chebyshev filter */
{
gint np = filter->poles;
gdouble *a, *b;
gint i, p;
a = g_new0 (gdouble, np + 3);
b = g_new0 (gdouble, np + 3);
/* Calculate transfer function coefficients */
a[2] = 1.0;
b[2] = 1.0;
for (p = 1; p <= np / 2; p++) {
gdouble a0, a1, a2, b1, b2;
gdouble *ta = g_new0 (gdouble, np + 3);
gdouble *tb = g_new0 (gdouble, np + 3);
generate_biquad_coefficients (filter, p, &a0, &a1, &a2, &b1, &b2);
memcpy (ta, a, sizeof (gdouble) * (np + 3));
memcpy (tb, b, sizeof (gdouble) * (np + 3));
/* add the new coefficients for the new two poles
* to the cascade by multiplication of the transfer
* functions */
for (i = 2; i < np + 3; i++) {
a[i] = a0 * ta[i] + a1 * ta[i - 1] + a2 * ta[i - 2];
b[i] = tb[i] - b1 * tb[i - 1] - b2 * tb[i - 2];
}
g_free (ta);
g_free (tb);
}
/* Move coefficients to the beginning of the array
* and multiply the b coefficients with -1 to move from
* the transfer function's coefficients to the difference
* equation's coefficients */
b[2] = 0.0;
for (i = 0; i <= np; i++) {
a[i] = a[i + 2];
b[i] = -b[i + 2];
}
/* Normalize to unity gain at frequency 0 for lowpass
* and frequency 0.5 for highpass */
{
gdouble gain;
if (filter->mode == MODE_LOW_PASS)
gain =
gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1,
1.0, 0.0);
else
gain =
gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1,
-1.0, 0.0);
for (i = 0; i <= np; i++) {
a[i] /= gain;
}
}
gst_audio_fx_base_iir_filter_set_coefficients (GST_AUDIO_FX_BASE_IIR_FILTER
(filter), a, np + 1, b, np + 1);
GST_LOG_OBJECT (filter,
"Generated IIR coefficients for the Chebyshev filter");
GST_LOG_OBJECT (filter,
"mode: %s, type: %d, poles: %d, cutoff: %.2f Hz, ripple: %.2f dB",
(filter->mode == MODE_LOW_PASS) ? "low-pass" : "high-pass",
filter->type, filter->poles, filter->cutoff, filter->ripple);
GST_LOG_OBJECT (filter, "%.2f dB gain @ 0 Hz",
20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b,
np + 1, 1.0, 0.0)));
#ifndef GST_DISABLE_GST_DEBUG
{
gdouble wc =
2.0 * M_PI * (filter->cutoff /
GST_AUDIO_FILTER (filter)->format.rate);
gdouble zr = cos (wc), zi = sin (wc);
GST_LOG_OBJECT (filter, "%.2f dB gain @ %d Hz",
20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1,
b, np + 1, zr, zi)), (int) filter->cutoff);
}
#endif
GST_LOG_OBJECT (filter, "%.2f dB gain @ %d Hz",
20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b,
np + 1, -1.0, 0.0)),
GST_AUDIO_FILTER (filter)->format.rate / 2);
}
}
static void
gst_audio_cheb_limit_finalize (GObject * object)
{
GstAudioChebLimit *filter = GST_AUDIO_CHEB_LIMIT (object);
g_mutex_free (filter->lock);
filter->lock = NULL;
G_OBJECT_CLASS (parent_class)->finalize (object);
}
static void
gst_audio_cheb_limit_set_property (GObject * object, guint prop_id,
const GValue * value, GParamSpec * pspec)
{
GstAudioChebLimit *filter = GST_AUDIO_CHEB_LIMIT (object);
switch (prop_id) {
case PROP_MODE:
g_mutex_lock (filter->lock);
filter->mode = g_value_get_enum (value);
generate_coefficients (filter);
g_mutex_unlock (filter->lock);
break;
case PROP_TYPE:
g_mutex_lock (filter->lock);
filter->type = g_value_get_int (value);
generate_coefficients (filter);
g_mutex_unlock (filter->lock);
break;
case PROP_CUTOFF:
g_mutex_lock (filter->lock);
filter->cutoff = g_value_get_float (value);
generate_coefficients (filter);
g_mutex_unlock (filter->lock);
break;
case PROP_RIPPLE:
g_mutex_lock (filter->lock);
filter->ripple = g_value_get_float (value);
generate_coefficients (filter);
g_mutex_unlock (filter->lock);
break;
case PROP_POLES:
g_mutex_lock (filter->lock);
filter->poles = GST_ROUND_UP_2 (g_value_get_int (value));
generate_coefficients (filter);
g_mutex_unlock (filter->lock);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
break;
}
}
static void
gst_audio_cheb_limit_get_property (GObject * object, guint prop_id,
GValue * value, GParamSpec * pspec)
{
GstAudioChebLimit *filter = GST_AUDIO_CHEB_LIMIT (object);
switch (prop_id) {
case PROP_MODE:
g_value_set_enum (value, filter->mode);
break;
case PROP_TYPE:
g_value_set_int (value, filter->type);
break;
case PROP_CUTOFF:
g_value_set_float (value, filter->cutoff);
break;
case PROP_RIPPLE:
g_value_set_float (value, filter->ripple);
break;
case PROP_POLES:
g_value_set_int (value, filter->poles);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
break;
}
}
/* GstAudioFilter vmethod implementations */
static gboolean
gst_audio_cheb_limit_setup (GstAudioFilter * base, GstRingBufferSpec * format)
{
GstAudioChebLimit *filter = GST_AUDIO_CHEB_LIMIT (base);
generate_coefficients (filter);
return GST_AUDIO_FILTER_CLASS (parent_class)->setup (base, format);
}