From 27ea0b076a1f1d44c3da1c677eddf62d01eef1f1 Mon Sep 17 00:00:00 2001 From: Stefan Kost Date: Wed, 7 Oct 2009 00:33:49 +0300 Subject: equalizer: use shelfing filters for first and last band 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. --- gst/equalizer/gstiirequalizer.c | 200 +++++++++++++++++++++++++++++----------- 1 file changed, 145 insertions(+), 55 deletions(-) diff --git a/gst/equalizer/gstiirequalizer.c b/gst/equalizer/gstiirequalizer.c index b671b247..0e481c68 100644 --- a/gst/equalizer/gstiirequalizer.c +++ b/gst/equalizer/gstiirequalizer.c @@ -121,10 +121,6 @@ struct _GstIirEqualizerBandClass 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 gst_iir_equalizer_band_set_property (GObject * object, guint prop_id, const GValue * value, GParamSpec * pspec) @@ -357,12 +353,6 @@ gst_iir_equalizer_finalize (GObject * 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 * * The Equivalence of Various Methods of Computing @@ -372,66 +362,163 @@ arg_to_scale (gdouble arg) * * http://www.aes.org/e-lib/browse.cfm?elib=6326 * 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 * one from this article transformed from octaves to frequency * in Hz. */ +static inline gdouble +arg_to_scale (gdouble arg) +{ + return (pow (10.0, arg / 40.0)); +} + +static gdouble +calculate_omega (gdouble freq, gint rate) +{ + gdouble omega; + + if (freq / rate >= 0.5) + omega = M_PI; + else if (freq <= 0.0) + omega = 0.0; + else + omega = 2.0 * M_PI * (freq / rate); + + 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) + * 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; + } else { + bw = 2.0 * M_PI * (band->width / rate); + } + return bw; +} + static void -setup_filter (GstIirEqualizer * equ, GstIirEqualizerBand * band) +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_low_shelf_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; + 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; - 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; + + 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; - } else { - bw = 2.0 * M_PI * (band->width / GST_AUDIO_FILTER (equ)->format.rate); - } - edge_gain = sqrt (gain); - gamma = tan (bw / 2.0); + egm = gain - 1.0; + egp = gain + 1.0; + alpha = tan (bw / 2.0); - alpha = gamma * edge_gain; - beta = gamma / edge_gain; + 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: GST_INFO @@ -459,11 +546,14 @@ set_passthrough (GstIirEqualizer * equ) static void update_coefficients (GstIirEqualizer * equ) { - gint i; + gint i, n = equ->freq_band_count; - for (i = 0; i < equ->freq_band_count; i++) { - setup_filter (equ, equ->bands[i]); + setup_low_shelf_filter (equ, equ->bands[0]); + 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; } -- cgit