3 * Copyright (C) 2007-2009 Sebastian Dröge <sebastian.droege@collabora.co.uk>
5 * This library is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU Library General Public
7 * License as published by the Free Software Foundation; either
8 * version 2 of the License, or (at your option) any later version.
10 * This library is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * Library General Public License for more details.
15 * You should have received a copy of the GNU Library General Public
16 * License along with this library; if not, write to the
17 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
18 * Boston, MA 02111-1307, USA.
22 * Chebyshev type 1 filter design based on
23 * "The Scientist and Engineer's Guide to DSP", Chapter 20.
24 * http://www.dspguide.com/
26 * For type 2 and Chebyshev filters in general read
27 * http://en.wikipedia.org/wiki/Chebyshev_filter
29 * Transformation from lowpass to bandpass/bandreject:
30 * http://docs.dewresearch.com/DspHelp/html/IDH_LinearSystems_LowpassToBandPassZ.htm
31 * http://docs.dewresearch.com/DspHelp/html/IDH_LinearSystems_LowpassToBandStopZ.htm
36 * SECTION:element-audiochebband
38 * Attenuates all frequencies outside (bandpass) or inside (bandreject) of a frequency
39 * band. The number of poles and the ripple parameter control the rolloff.
41 * This element has the advantage over the windowed sinc bandpass and bandreject filter that it is
42 * much faster and produces almost as good results. It's only disadvantages are the highly
43 * non-linear phase and the slower rolloff compared to a windowed sinc filter with a large kernel.
45 * For type 1 the ripple parameter specifies how much ripple in dB is allowed in the passband, i.e.
46 * some frequencies in the passband will be amplified by that value. A higher ripple value will allow
49 * For type 2 the ripple parameter specifies the stopband attenuation. In the stopband the gain will
50 * be at most this value. A lower ripple value will allow a faster rolloff.
52 * As a special case, a Chebyshev type 1 filter with no ripple is a Butterworth filter.
55 * Be warned that a too large number of poles can produce noise. The most poles are possible with
56 * a cutoff frequency at a quarter of the sampling rate.
60 * <title>Example launch line</title>
62 * gst-launch audiotestsrc freq=1500 ! audioconvert ! audiochebband mode=band-pass lower-frequency=1000 upper-frequenc=6000 poles=4 ! audioconvert ! alsasink
63 * gst-launch filesrc location="melo1.ogg" ! oggdemux ! vorbisdec ! audioconvert ! audiochebband mode=band-reject lower-frequency=1000 upper-frequency=4000 ripple=0.2 ! audioconvert ! alsasink
64 * gst-launch audiotestsrc wave=white-noise ! audioconvert ! audiochebband mode=band-pass lower-frequency=1000 upper-frequency=4000 type=2 ! audioconvert ! alsasink
76 #include <gst/base/gstbasetransform.h>
77 #include <gst/audio/audio.h>
78 #include <gst/audio/gstaudiofilter.h>
82 #include "math_compat.h"
84 #include "audiochebband.h"
86 #include "gst/glib-compat-private.h"
88 #define GST_CAT_DEFAULT gst_audio_cheb_band_debug
89 GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);
102 #define gst_audio_cheb_band_parent_class parent_class
103 G_DEFINE_TYPE (GstAudioChebBand, gst_audio_cheb_band,
104 GST_TYPE_AUDIO_FX_BASE_IIR_FILTER);
106 static void gst_audio_cheb_band_set_property (GObject * object,
107 guint prop_id, const GValue * value, GParamSpec * pspec);
108 static void gst_audio_cheb_band_get_property (GObject * object,
109 guint prop_id, GValue * value, GParamSpec * pspec);
110 static void gst_audio_cheb_band_finalize (GObject * object);
112 static gboolean gst_audio_cheb_band_setup (GstAudioFilter * filter,
113 const GstAudioInfo * info);
121 #define GST_TYPE_AUDIO_CHEBYSHEV_FREQ_BAND_MODE (gst_audio_cheb_band_mode_get_type ())
123 gst_audio_cheb_band_mode_get_type (void)
125 static GType gtype = 0;
128 static const GEnumValue values[] = {
129 {MODE_BAND_PASS, "Band pass (default)",
131 {MODE_BAND_REJECT, "Band reject",
136 gtype = g_enum_register_static ("GstAudioChebBandMode", values);
141 /* GObject vmethod implementations */
144 gst_audio_cheb_band_class_init (GstAudioChebBandClass * klass)
146 GObjectClass *gobject_class = (GObjectClass *) klass;
147 GstElementClass *gstelement_class = (GstElementClass *) klass;
148 GstAudioFilterClass *filter_class = (GstAudioFilterClass *) klass;
150 GST_DEBUG_CATEGORY_INIT (gst_audio_cheb_band_debug, "audiochebband", 0,
151 "audiochebband element");
153 gobject_class->set_property = gst_audio_cheb_band_set_property;
154 gobject_class->get_property = gst_audio_cheb_band_get_property;
155 gobject_class->finalize = gst_audio_cheb_band_finalize;
157 g_object_class_install_property (gobject_class, PROP_MODE,
158 g_param_spec_enum ("mode", "Mode",
159 "Low pass or high pass mode", GST_TYPE_AUDIO_CHEBYSHEV_FREQ_BAND_MODE,
161 G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
162 g_object_class_install_property (gobject_class, PROP_TYPE,
163 g_param_spec_int ("type", "Type", "Type of the chebychev filter", 1, 2, 1,
164 G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
166 /* FIXME: Don't use the complete possible range but restrict the upper boundary
167 * so automatically generated UIs can use a slider without */
168 g_object_class_install_property (gobject_class, PROP_LOWER_FREQUENCY,
169 g_param_spec_float ("lower-frequency", "Lower frequency",
170 "Start frequency of the band (Hz)", 0.0, 100000.0,
172 G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
173 g_object_class_install_property (gobject_class, PROP_UPPER_FREQUENCY,
174 g_param_spec_float ("upper-frequency", "Upper frequency",
175 "Stop frequency of the band (Hz)", 0.0, 100000.0, 0.0,
176 G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
177 g_object_class_install_property (gobject_class, PROP_RIPPLE,
178 g_param_spec_float ("ripple", "Ripple", "Amount of ripple (dB)", 0.0,
180 G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
181 /* FIXME: What to do about this upper boundary? With a frequencies near
182 * rate/4 32 poles are completely possible, with frequencies very low
183 * or very high 16 poles already produces only noise */
184 g_object_class_install_property (gobject_class, PROP_POLES,
185 g_param_spec_int ("poles", "Poles",
186 "Number of poles to use, will be rounded up to the next multiply of four",
188 G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
190 gst_element_class_set_details_simple (gstelement_class,
191 "Band pass & band reject filter", "Filter/Effect/Audio",
192 "Chebyshev band pass and band reject filter",
193 "Sebastian Dröge <sebastian.droege@collabora.co.uk>");
195 filter_class->setup = GST_DEBUG_FUNCPTR (gst_audio_cheb_band_setup);
199 gst_audio_cheb_band_init (GstAudioChebBand * filter)
201 filter->lower_frequency = filter->upper_frequency = 0.0;
202 filter->mode = MODE_BAND_PASS;
205 filter->ripple = 0.25;
207 g_mutex_init (&filter->lock);
211 generate_biquad_coefficients (GstAudioChebBand * filter,
212 gint p, gdouble * b0, gdouble * b1, gdouble * b2, gdouble * b3,
213 gdouble * b4, gdouble * a1, gdouble * a2, gdouble * a3, gdouble * a4)
215 gint np = filter->poles / 2;
216 gdouble ripple = filter->ripple;
217 gint rate = GST_AUDIO_FILTER_RATE (filter);
219 /* pole location in s-plane */
222 /* zero location in s-plane */
225 /* transfer function coefficients for the z-plane */
226 gdouble x0, x1, x2, y1, y2;
227 gint type = filter->type;
229 /* Calculate pole location for lowpass at frequency 1 */
231 gdouble angle = (G_PI / 2.0) * (2.0 * p - 1) / np;
237 /* If we allow ripple, move the pole from the unit
238 * circle to an ellipse and keep cutoff at frequency 1 */
239 if (ripple > 0 && type == 1) {
242 es = sqrt (pow (10.0, ripple / 10.0) - 1.0);
244 vx = (1.0 / np) * asinh (1.0 / es);
247 } else if (type == 2) {
250 es = sqrt (pow (10.0, ripple / 10.0) - 1.0);
251 vx = (1.0 / np) * asinh (es);
256 /* Calculate inverse of the pole location to move from
257 * type I to type II */
259 gdouble mag2 = rp * rp + ip * ip;
265 /* Calculate zero location for frequency 1 on the
266 * unit circle for type 2 */
268 gdouble angle = G_PI / (np * 2.0) + ((p - 1) * G_PI) / (np);
276 /* Convert from s-domain to z-domain by
277 * using the bilinear Z-transform, i.e.
278 * substitute s by (2/t)*((z-1)/(z+1))
279 * with t = 2 * tan(0.5).
285 m = rp * rp + ip * ip;
286 d = 4.0 - 4.0 * rp * t + m * t * t;
291 y1 = (8.0 - 2.0 * m * t * t) / d;
292 y2 = (-4.0 - 4.0 * rp * t - m * t * t) / d;
297 m = rp * rp + ip * ip;
298 d = 4.0 - 4.0 * rp * t + m * t * t;
300 x0 = (t * t * iz * iz + 4.0) / d;
301 x1 = (-8.0 + 2.0 * iz * iz * t * t) / d;
303 y1 = (8.0 - 2.0 * m * t * t) / d;
304 y2 = (-4.0 - 4.0 * rp * t - m * t * t) / d;
307 /* Convert from lowpass at frequency 1 to either bandpass
310 * For bandpass substitute z^(-1) with:
313 * -z + alpha * z - beta
314 * ----------------------------
316 * beta * z - alpha * z + 1
318 * alpha = (2*a*b)/(1+b)
320 * a = cos((w1 + w0)/2) / cos((w1 - w0)/2)
321 * b = tan(1/2) * cot((w1 - w0)/2)
323 * For bandreject substitute z^(-1) with:
326 * z - alpha * z + beta
327 * ----------------------------
329 * beta * z - alpha * z + 1
331 * alpha = (2*a)/(1+b)
333 * a = cos((w1 + w0)/2) / cos((w1 - w0)/2)
334 * b = tan(1/2) * tan((w1 - w0)/2)
340 gdouble w0 = 2.0 * G_PI * (filter->lower_frequency / rate);
341 gdouble w1 = 2.0 * G_PI * (filter->upper_frequency / rate);
343 if (filter->mode == MODE_BAND_PASS) {
344 a = cos ((w1 + w0) / 2.0) / cos ((w1 - w0) / 2.0);
345 b = tan (1.0 / 2.0) / tan ((w1 - w0) / 2.0);
347 alpha = (2.0 * a * b) / (1.0 + b);
348 beta = (b - 1.0) / (b + 1.0);
350 d = 1.0 + beta * (y1 - beta * y2);
352 *b0 = (x0 + beta * (-x1 + beta * x2)) / d;
353 *b1 = (alpha * (-2.0 * x0 + x1 + beta * x1 - 2.0 * beta * x2)) / d;
355 (-x1 - beta * beta * x1 + 2.0 * beta * (x0 + x2) +
356 alpha * alpha * (x0 - x1 + x2)) / d;
357 *b3 = (alpha * (x1 + beta * (-2.0 * x0 + x1) - 2.0 * x2)) / d;
358 *b4 = (beta * (beta * x0 - x1) + x2) / d;
359 *a1 = (alpha * (2.0 + y1 + beta * y1 - 2.0 * beta * y2)) / d;
361 (-y1 - beta * beta * y1 - alpha * alpha * (1.0 + y1 - y2) +
362 2.0 * beta * (-1.0 + y2)) / d;
363 *a3 = (alpha * (y1 + beta * (2.0 + y1) - 2.0 * y2)) / d;
364 *a4 = (-beta * beta - beta * y1 + y2) / d;
366 a = cos ((w1 + w0) / 2.0) / cos ((w1 - w0) / 2.0);
367 b = tan (1.0 / 2.0) * tan ((w1 - w0) / 2.0);
369 alpha = (2.0 * a) / (1.0 + b);
370 beta = (1.0 - b) / (1.0 + b);
372 d = -1.0 + beta * (beta * y2 + y1);
374 *b0 = (-x0 - beta * x1 - beta * beta * x2) / d;
375 *b1 = (alpha * (2.0 * x0 + x1 + beta * x1 + 2.0 * beta * x2)) / d;
377 (-x1 - beta * beta * x1 - 2.0 * beta * (x0 + x2) -
378 alpha * alpha * (x0 + x1 + x2)) / d;
379 *b3 = (alpha * (x1 + beta * (2.0 * x0 + x1) + 2.0 * x2)) / d;
380 *b4 = (-beta * beta * x0 - beta * x1 - x2) / d;
381 *a1 = (alpha * (-2.0 + y1 + beta * y1 + 2.0 * beta * y2)) / d;
383 -(y1 + beta * beta * y1 + 2.0 * beta * (-1.0 + y2) +
384 alpha * alpha * (-1.0 + y1 + y2)) / d;
385 *a3 = (alpha * (beta * (-2.0 + y1) + y1 + 2.0 * y2)) / d;
386 *a4 = -(-beta * beta + beta * y1 + y2) / d;
392 generate_coefficients (GstAudioChebBand * filter, const GstAudioInfo * info)
397 rate = GST_AUDIO_INFO_RATE (info);
399 rate = GST_AUDIO_FILTER_RATE (filter);
403 gdouble *a = g_new0 (gdouble, 1);
404 gdouble *b = g_new0 (gdouble, 1);
408 gst_audio_fx_base_iir_filter_set_coefficients (GST_AUDIO_FX_BASE_IIR_FILTER
409 (filter), a, 1, b, 1);
410 GST_LOG_OBJECT (filter, "rate was not set yet");
414 if (filter->upper_frequency <= filter->lower_frequency) {
415 gdouble *a = g_new0 (gdouble, 1);
416 gdouble *b = g_new0 (gdouble, 1);
419 b[0] = (filter->mode == MODE_BAND_PASS) ? 0.0 : 1.0;
420 gst_audio_fx_base_iir_filter_set_coefficients (GST_AUDIO_FX_BASE_IIR_FILTER
421 (filter), a, 1, b, 1);
423 GST_LOG_OBJECT (filter, "frequency band had no or negative dimension");
427 if (filter->upper_frequency > rate / 2) {
428 filter->upper_frequency = rate / 2;
429 GST_LOG_OBJECT (filter, "clipped upper frequency to nyquist frequency");
432 if (filter->lower_frequency < 0.0) {
433 filter->lower_frequency = 0.0;
434 GST_LOG_OBJECT (filter, "clipped lower frequency to 0.0");
437 /* Calculate coefficients for the chebyshev filter */
439 gint np = filter->poles;
443 a = g_new0 (gdouble, np + 5);
444 b = g_new0 (gdouble, np + 5);
446 /* Calculate transfer function coefficients */
450 for (p = 1; p <= np / 4; p++) {
451 gdouble b0, b1, b2, b3, b4, a1, a2, a3, a4;
452 gdouble *ta = g_new0 (gdouble, np + 5);
453 gdouble *tb = g_new0 (gdouble, np + 5);
455 generate_biquad_coefficients (filter, p, &b0, &b1, &b2, &b3, &b4, &a1,
458 memcpy (ta, a, sizeof (gdouble) * (np + 5));
459 memcpy (tb, b, sizeof (gdouble) * (np + 5));
461 /* add the new coefficients for the new two poles
462 * to the cascade by multiplication of the transfer
464 for (i = 4; i < np + 5; i++) {
466 b0 * tb[i] + b1 * tb[i - 1] + b2 * tb[i - 2] + b3 * tb[i - 3] +
469 ta[i] - a1 * ta[i - 1] - a2 * ta[i - 2] - a3 * ta[i - 3] -
476 /* Move coefficients to the beginning of the array to move from
477 * the transfer function's coefficients to the difference
478 * equation's coefficients */
479 for (i = 0; i <= np; i++) {
484 /* Normalize to unity gain at frequency 0 and frequency
485 * 0.5 for bandreject and unity gain at band center frequency
487 if (filter->mode == MODE_BAND_REJECT) {
488 /* gain is sqrt(H(0)*H(0.5)) */
491 gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1,
494 gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1,
497 gain1 = sqrt (gain1 * gain2);
499 for (i = 0; i <= np; i++) {
503 /* gain is H(wc), wc = center frequency */
505 gdouble w1 = 2.0 * G_PI * (filter->lower_frequency / rate);
506 gdouble w2 = 2.0 * G_PI * (filter->upper_frequency / rate);
507 gdouble w0 = (w2 + w1) / 2.0;
508 gdouble zr = cos (w0), zi = sin (w0);
510 gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1, zr,
513 for (i = 0; i <= np; i++) {
518 gst_audio_fx_base_iir_filter_set_coefficients (GST_AUDIO_FX_BASE_IIR_FILTER
519 (filter), a, np + 1, b, np + 1);
521 GST_LOG_OBJECT (filter,
522 "Generated IIR coefficients for the Chebyshev filter");
523 GST_LOG_OBJECT (filter,
524 "mode: %s, type: %d, poles: %d, lower-frequency: %.2f Hz, upper-frequency: %.2f Hz, ripple: %.2f dB",
525 (filter->mode == MODE_BAND_PASS) ? "band-pass" : "band-reject",
526 filter->type, filter->poles, filter->lower_frequency,
527 filter->upper_frequency, filter->ripple);
529 GST_LOG_OBJECT (filter, "%.2f dB gain @ 0Hz",
530 20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b,
533 gdouble w1 = 2.0 * G_PI * (filter->lower_frequency / rate);
534 gdouble w2 = 2.0 * G_PI * (filter->upper_frequency / rate);
535 gdouble w0 = (w2 + w1) / 2.0;
540 GST_LOG_OBJECT (filter, "%.2f dB gain @ %dHz",
541 20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1,
542 b, np + 1, zr, zi)), (int) filter->lower_frequency);
545 GST_LOG_OBJECT (filter, "%.2f dB gain @ %dHz",
546 20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1,
548 (int) ((filter->lower_frequency + filter->upper_frequency) / 2.0));
551 GST_LOG_OBJECT (filter, "%.2f dB gain @ %dHz",
552 20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1,
553 b, np + 1, zr, zi)), (int) filter->upper_frequency);
555 GST_LOG_OBJECT (filter, "%.2f dB gain @ %dHz",
556 20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b,
557 np + 1, -1.0, 0.0)), rate / 2);
562 gst_audio_cheb_band_finalize (GObject * object)
564 GstAudioChebBand *filter = GST_AUDIO_CHEB_BAND (object);
566 g_mutex_clear (&filter->lock);
568 G_OBJECT_CLASS (parent_class)->finalize (object);
572 gst_audio_cheb_band_set_property (GObject * object, guint prop_id,
573 const GValue * value, GParamSpec * pspec)
575 GstAudioChebBand *filter = GST_AUDIO_CHEB_BAND (object);
579 g_mutex_lock (&filter->lock);
580 filter->mode = g_value_get_enum (value);
581 generate_coefficients (filter, NULL);
582 g_mutex_unlock (&filter->lock);
585 g_mutex_lock (&filter->lock);
586 filter->type = g_value_get_int (value);
587 generate_coefficients (filter, NULL);
588 g_mutex_unlock (&filter->lock);
590 case PROP_LOWER_FREQUENCY:
591 g_mutex_lock (&filter->lock);
592 filter->lower_frequency = g_value_get_float (value);
593 generate_coefficients (filter, NULL);
594 g_mutex_unlock (&filter->lock);
596 case PROP_UPPER_FREQUENCY:
597 g_mutex_lock (&filter->lock);
598 filter->upper_frequency = g_value_get_float (value);
599 generate_coefficients (filter, NULL);
600 g_mutex_unlock (&filter->lock);
603 g_mutex_lock (&filter->lock);
604 filter->ripple = g_value_get_float (value);
605 generate_coefficients (filter, NULL);
606 g_mutex_unlock (&filter->lock);
609 g_mutex_lock (&filter->lock);
610 filter->poles = GST_ROUND_UP_4 (g_value_get_int (value));
611 generate_coefficients (filter, NULL);
612 g_mutex_unlock (&filter->lock);
615 G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
621 gst_audio_cheb_band_get_property (GObject * object, guint prop_id,
622 GValue * value, GParamSpec * pspec)
624 GstAudioChebBand *filter = GST_AUDIO_CHEB_BAND (object);
628 g_value_set_enum (value, filter->mode);
631 g_value_set_int (value, filter->type);
633 case PROP_LOWER_FREQUENCY:
634 g_value_set_float (value, filter->lower_frequency);
636 case PROP_UPPER_FREQUENCY:
637 g_value_set_float (value, filter->upper_frequency);
640 g_value_set_float (value, filter->ripple);
643 g_value_set_int (value, filter->poles);
646 G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
651 /* GstAudioFilter vmethod implementations */
654 gst_audio_cheb_band_setup (GstAudioFilter * base, const GstAudioInfo * info)
656 GstAudioChebBand *filter = GST_AUDIO_CHEB_BAND (base);
658 generate_coefficients (filter, info);
660 return GST_AUDIO_FILTER_CLASS (parent_class)->setup (base, info);