/* * GStreamer * Copyright (C) 2007-2009 Sebastian Dröge * * 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 * * Transformation from lowpass to bandpass/bandreject: * http://docs.dewresearch.com/DspHelp/html/IDH_LinearSystems_LowpassToBandPassZ.htm * http://docs.dewresearch.com/DspHelp/html/IDH_LinearSystems_LowpassToBandStopZ.htm * */ /** * SECTION:element-audiochebband * * Attenuates all frequencies outside (bandpass) or inside (bandreject) of a frequency * band. The number of poles and the ripple parameter control the rolloff. * * This element has the advantage over the windowed sinc bandpass and bandreject 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. * * * 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. * * * * Example launch line * |[ * gst-launch audiotestsrc freq=1500 ! audioconvert ! audiochebband mode=band-pass lower-frequency=1000 upper-frequenc=6000 poles=4 ! audioconvert ! alsasink * gst-launch filesrc location="melo1.ogg" ! oggdemux ! vorbisdec ! audioconvert ! audiochebband mode=band-reject lower-frequency=1000 upper-frequency=4000 ripple=0.2 ! audioconvert ! alsasink * gst-launch audiotestsrc wave=white-noise ! audioconvert ! audiochebband mode=band-pass lower-frequency=1000 upper-frequency=4000 type=2 ! audioconvert ! alsasink * ]| * */ #ifdef HAVE_CONFIG_H #include "config.h" #endif #include #include #include #include #include #include #include "math_compat.h" #include "audiochebband.h" #include "gst/glib-compat-private.h" #define GST_CAT_DEFAULT gst_audio_cheb_band_debug GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT); enum { PROP_0, PROP_MODE, PROP_TYPE, PROP_LOWER_FREQUENCY, PROP_UPPER_FREQUENCY, PROP_RIPPLE, PROP_POLES }; #define gst_audio_cheb_band_parent_class parent_class G_DEFINE_TYPE (GstAudioChebBand, gst_audio_cheb_band, GST_TYPE_AUDIO_FX_BASE_IIR_FILTER); static void gst_audio_cheb_band_set_property (GObject * object, guint prop_id, const GValue * value, GParamSpec * pspec); static void gst_audio_cheb_band_get_property (GObject * object, guint prop_id, GValue * value, GParamSpec * pspec); static void gst_audio_cheb_band_finalize (GObject * object); static gboolean gst_audio_cheb_band_setup (GstAudioFilter * filter, const GstAudioInfo * info); enum { MODE_BAND_PASS = 0, MODE_BAND_REJECT }; #define GST_TYPE_AUDIO_CHEBYSHEV_FREQ_BAND_MODE (gst_audio_cheb_band_mode_get_type ()) static GType gst_audio_cheb_band_mode_get_type (void) { static GType gtype = 0; if (gtype == 0) { static const GEnumValue values[] = { {MODE_BAND_PASS, "Band pass (default)", "band-pass"}, {MODE_BAND_REJECT, "Band reject", "band-reject"}, {0, NULL, NULL} }; gtype = g_enum_register_static ("GstAudioChebBandMode", values); } return gtype; } /* GObject vmethod implementations */ static void gst_audio_cheb_band_class_init (GstAudioChebBandClass * klass) { GObjectClass *gobject_class = (GObjectClass *) klass; GstElementClass *gstelement_class = (GstElementClass *) klass; GstAudioFilterClass *filter_class = (GstAudioFilterClass *) klass; GST_DEBUG_CATEGORY_INIT (gst_audio_cheb_band_debug, "audiochebband", 0, "audiochebband element"); gobject_class->set_property = gst_audio_cheb_band_set_property; gobject_class->get_property = gst_audio_cheb_band_get_property; gobject_class->finalize = gst_audio_cheb_band_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_BAND_MODE, MODE_BAND_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_LOWER_FREQUENCY, g_param_spec_float ("lower-frequency", "Lower frequency", "Start frequency of the band (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_UPPER_FREQUENCY, g_param_spec_float ("upper-frequency", "Upper frequency", "Stop frequency of the band (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 frequencies near * rate/4 32 poles are completely possible, with frequencies 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 multiply of four", 4, 32, 4, G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS)); gst_element_class_set_details_simple (gstelement_class, "Band pass & band reject filter", "Filter/Effect/Audio", "Chebyshev band pass and band reject filter", "Sebastian Dröge "); filter_class->setup = GST_DEBUG_FUNCPTR (gst_audio_cheb_band_setup); } static void gst_audio_cheb_band_init (GstAudioChebBand * filter) { filter->lower_frequency = filter->upper_frequency = 0.0; filter->mode = MODE_BAND_PASS; filter->type = 1; filter->poles = 4; filter->ripple = 0.25; g_mutex_init (&filter->lock); } static void generate_biquad_coefficients (GstAudioChebBand * filter, gint p, gdouble * b0, gdouble * b1, gdouble * b2, gdouble * b3, gdouble * b4, gdouble * a1, gdouble * a2, gdouble * a3, gdouble * a4) { gint np = filter->poles / 2; gdouble ripple = filter->ripple; gint rate = GST_AUDIO_FILTER_RATE (filter); /* 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 = (G_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 move 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 = G_PI / (np * 2.0) + ((p - 1) * G_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 bandpass * or band reject. * * For bandpass substitute z^(-1) with: * * -2 -1 * -z + alpha * z - beta * ---------------------------- * -2 -1 * beta * z - alpha * z + 1 * * alpha = (2*a*b)/(1+b) * beta = (b-1)/(b+1) * a = cos((w1 + w0)/2) / cos((w1 - w0)/2) * b = tan(1/2) * cot((w1 - w0)/2) * * For bandreject substitute z^(-1) with: * * -2 -1 * z - alpha * z + beta * ---------------------------- * -2 -1 * beta * z - alpha * z + 1 * * alpha = (2*a)/(1+b) * beta = (1-b)/(1+b) * a = cos((w1 + w0)/2) / cos((w1 - w0)/2) * b = tan(1/2) * tan((w1 - w0)/2) * */ { gdouble a, b, d; gdouble alpha, beta; gdouble w0 = 2.0 * G_PI * (filter->lower_frequency / rate); gdouble w1 = 2.0 * G_PI * (filter->upper_frequency / rate); if (filter->mode == MODE_BAND_PASS) { a = cos ((w1 + w0) / 2.0) / cos ((w1 - w0) / 2.0); b = tan (1.0 / 2.0) / tan ((w1 - w0) / 2.0); alpha = (2.0 * a * b) / (1.0 + b); beta = (b - 1.0) / (b + 1.0); d = 1.0 + beta * (y1 - beta * y2); *b0 = (x0 + beta * (-x1 + beta * x2)) / d; *b1 = (alpha * (-2.0 * x0 + x1 + beta * x1 - 2.0 * beta * x2)) / d; *b2 = (-x1 - beta * beta * x1 + 2.0 * beta * (x0 + x2) + alpha * alpha * (x0 - x1 + x2)) / d; *b3 = (alpha * (x1 + beta * (-2.0 * x0 + x1) - 2.0 * x2)) / d; *b4 = (beta * (beta * x0 - x1) + x2) / d; *a1 = (alpha * (2.0 + y1 + beta * y1 - 2.0 * beta * y2)) / d; *a2 = (-y1 - beta * beta * y1 - alpha * alpha * (1.0 + y1 - y2) + 2.0 * beta * (-1.0 + y2)) / d; *a3 = (alpha * (y1 + beta * (2.0 + y1) - 2.0 * y2)) / d; *a4 = (-beta * beta - beta * y1 + y2) / d; } else { a = cos ((w1 + w0) / 2.0) / cos ((w1 - w0) / 2.0); b = tan (1.0 / 2.0) * tan ((w1 - w0) / 2.0); alpha = (2.0 * a) / (1.0 + b); beta = (1.0 - b) / (1.0 + b); d = -1.0 + beta * (beta * y2 + y1); *b0 = (-x0 - beta * x1 - beta * beta * x2) / d; *b1 = (alpha * (2.0 * x0 + x1 + beta * x1 + 2.0 * beta * x2)) / d; *b2 = (-x1 - beta * beta * x1 - 2.0 * beta * (x0 + x2) - alpha * alpha * (x0 + x1 + x2)) / d; *b3 = (alpha * (x1 + beta * (2.0 * x0 + x1) + 2.0 * x2)) / d; *b4 = (-beta * beta * x0 - beta * x1 - x2) / d; *a1 = (alpha * (-2.0 + y1 + beta * y1 + 2.0 * beta * y2)) / d; *a2 = -(y1 + beta * beta * y1 + 2.0 * beta * (-1.0 + y2) + alpha * alpha * (-1.0 + y1 + y2)) / d; *a3 = (alpha * (beta * (-2.0 + y1) + y1 + 2.0 * y2)) / d; *a4 = -(-beta * beta + beta * y1 + y2) / d; } } } static void generate_coefficients (GstAudioChebBand * filter) { gint rate = GST_AUDIO_FILTER_RATE (filter); if (rate == 0) { gdouble *a = g_new0 (gdouble, 1); gdouble *b = g_new0 (gdouble, 1); a[0] = 1.0; b[0] = 1.0; gst_audio_fx_base_iir_filter_set_coefficients (GST_AUDIO_FX_BASE_IIR_FILTER (filter), a, 1, b, 1); GST_LOG_OBJECT (filter, "rate was not set yet"); return; } if (filter->upper_frequency <= filter->lower_frequency) { gdouble *a = g_new0 (gdouble, 1); gdouble *b = g_new0 (gdouble, 1); a[0] = 1.0; b[0] = (filter->mode == MODE_BAND_PASS) ? 0.0 : 1.0; gst_audio_fx_base_iir_filter_set_coefficients (GST_AUDIO_FX_BASE_IIR_FILTER (filter), a, 1, b, 1); GST_LOG_OBJECT (filter, "frequency band had no or negative dimension"); return; } if (filter->upper_frequency > rate / 2) { filter->upper_frequency = rate / 2; GST_LOG_OBJECT (filter, "clipped upper frequency to nyquist frequency"); } if (filter->lower_frequency < 0.0) { filter->lower_frequency = 0.0; GST_LOG_OBJECT (filter, "clipped lower frequency to 0.0"); } /* Calculate coefficients for the chebyshev filter */ { gint np = filter->poles; gdouble *a, *b; gint i, p; a = g_new0 (gdouble, np + 5); b = g_new0 (gdouble, np + 5); /* Calculate transfer function coefficients */ a[4] = 1.0; b[4] = 1.0; for (p = 1; p <= np / 4; p++) { gdouble b0, b1, b2, b3, b4, a1, a2, a3, a4; gdouble *ta = g_new0 (gdouble, np + 5); gdouble *tb = g_new0 (gdouble, np + 5); generate_biquad_coefficients (filter, p, &b0, &b1, &b2, &b3, &b4, &a1, &a2, &a3, &a4); memcpy (ta, a, sizeof (gdouble) * (np + 5)); memcpy (tb, b, sizeof (gdouble) * (np + 5)); /* add the new coefficients for the new two poles * to the cascade by multiplication of the transfer * functions */ for (i = 4; i < np + 5; i++) { b[i] = b0 * tb[i] + b1 * tb[i - 1] + b2 * tb[i - 2] + b3 * tb[i - 3] + b4 * tb[i - 4]; a[i] = ta[i] - a1 * ta[i - 1] - a2 * ta[i - 2] - a3 * ta[i - 3] - a4 * ta[i - 4]; } g_free (ta); g_free (tb); } /* Move coefficients to the beginning of the array to move from * the transfer function's coefficients to the difference * equation's coefficients */ for (i = 0; i <= np; i++) { a[i] = a[i + 4]; b[i] = b[i + 4]; } /* Normalize to unity gain at frequency 0 and frequency * 0.5 for bandreject and unity gain at band center frequency * for bandpass */ if (filter->mode == MODE_BAND_REJECT) { /* gain is sqrt(H(0)*H(0.5)) */ gdouble gain1 = gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1, 1.0, 0.0); gdouble gain2 = gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1, -1.0, 0.0); gain1 = sqrt (gain1 * gain2); for (i = 0; i <= np; i++) { b[i] /= gain1; } } else { /* gain is H(wc), wc = center frequency */ gdouble w1 = 2.0 * G_PI * (filter->lower_frequency / rate); gdouble w2 = 2.0 * G_PI * (filter->upper_frequency / rate); gdouble w0 = (w2 + w1) / 2.0; gdouble zr = cos (w0), zi = sin (w0); gdouble gain = gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1, zr, zi); for (i = 0; i <= np; i++) { b[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, lower-frequency: %.2f Hz, upper-frequency: %.2f Hz, ripple: %.2f dB", (filter->mode == MODE_BAND_PASS) ? "band-pass" : "band-reject", filter->type, filter->poles, filter->lower_frequency, filter->upper_frequency, filter->ripple); GST_LOG_OBJECT (filter, "%.2f dB gain @ 0Hz", 20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1, 1.0, 0.0))); { gdouble w1 = 2.0 * G_PI * (filter->lower_frequency / rate); gdouble w2 = 2.0 * G_PI * (filter->upper_frequency / rate); gdouble w0 = (w2 + w1) / 2.0; gdouble zr, zi; zr = cos (w1); zi = sin (w1); GST_LOG_OBJECT (filter, "%.2f dB gain @ %dHz", 20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1, zr, zi)), (int) filter->lower_frequency); zr = cos (w0); zi = sin (w0); GST_LOG_OBJECT (filter, "%.2f dB gain @ %dHz", 20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1, zr, zi)), (int) ((filter->lower_frequency + filter->upper_frequency) / 2.0)); zr = cos (w2); zi = sin (w2); GST_LOG_OBJECT (filter, "%.2f dB gain @ %dHz", 20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1, zr, zi)), (int) filter->upper_frequency); } GST_LOG_OBJECT (filter, "%.2f dB gain @ %dHz", 20.0 * log10 (gst_audio_fx_base_iir_filter_calculate_gain (a, np + 1, b, np + 1, -1.0, 0.0)), rate / 2); } } static void gst_audio_cheb_band_finalize (GObject * object) { GstAudioChebBand *filter = GST_AUDIO_CHEB_BAND (object); g_mutex_clear (&filter->lock); G_OBJECT_CLASS (parent_class)->finalize (object); } static void gst_audio_cheb_band_set_property (GObject * object, guint prop_id, const GValue * value, GParamSpec * pspec) { GstAudioChebBand *filter = GST_AUDIO_CHEB_BAND (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_LOWER_FREQUENCY: g_mutex_lock (&filter->lock); filter->lower_frequency = g_value_get_float (value); generate_coefficients (filter); g_mutex_unlock (&filter->lock); break; case PROP_UPPER_FREQUENCY: g_mutex_lock (&filter->lock); filter->upper_frequency = 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_4 (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_band_get_property (GObject * object, guint prop_id, GValue * value, GParamSpec * pspec) { GstAudioChebBand *filter = GST_AUDIO_CHEB_BAND (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_LOWER_FREQUENCY: g_value_set_float (value, filter->lower_frequency); break; case PROP_UPPER_FREQUENCY: g_value_set_float (value, filter->upper_frequency); 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_band_setup (GstAudioFilter * base, const GstAudioInfo * info) { GstAudioChebBand *filter = GST_AUDIO_CHEB_BAND (base); generate_coefficients (filter); return GST_AUDIO_FILTER_CLASS (parent_class)->setup (base, info); }