The chrome OS audio server has some already existing code, which
has been made available under a BSD-style license, which should be
safe to import by us.
Signed-off-by: David Henningsson <david.henningsson at canonical.com>
---
LICENSE | 3 +
src/pulsecore/filter/LICENSE.WEBKIT | 27 +++
src/pulsecore/filter/biquad.c | 368 ++++++++++++++++++++++++++++++++++++
src/pulsecore/filter/biquad.h | 57 ++++++
src/pulsecore/filter/crossover.c | 188 ++++++++++++++++++
src/pulsecore/filter/crossover.h | 70 +++++++
6 files changed, 713 insertions(+)
create mode 100644 src/pulsecore/filter/LICENSE.WEBKIT
create mode 100644 src/pulsecore/filter/biquad.c
create mode 100644 src/pulsecore/filter/biquad.h
create mode 100644 src/pulsecore/filter/crossover.c
create mode 100644 src/pulsecore/filter/crossover.h
diff --git a/LICENSE b/LICENSE
index 226c4ce..6932317 100644
--- a/LICENSE
+++ b/LICENSE
@@ -29,6 +29,9 @@ considered too small and stable to be considered as an external library) use the
more permissive MIT license. This include the device reservation DBus protocol
and realtime kit implementations.
+A more permissive BSD-style license is used for LFE filters, see
+src/pulsecore/filter/LICENSE.WEBKIT for details.
+
Additionally, a more permissive Sun license is used for code that performs
u-law, A-law and linear PCM conversions.
diff --git a/src/pulsecore/filter/LICENSE.WEBKIT b/src/pulsecore/filter/LICENSE.WEBKIT
new file mode 100644
index 0000000..2f69d9f
--- /dev/null
+++ b/src/pulsecore/filter/LICENSE.WEBKIT
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2010 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Apple Computer, Inc. ("Apple") nor the names of
+ * its contributors may be used to endorse or promote products derived
+ * from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
diff --git a/src/pulsecore/filter/biquad.c b/src/pulsecore/filter/biquad.c
new file mode 100644
index 0000000..b28256d
--- /dev/null
+++ b/src/pulsecore/filter/biquad.c
@@ -0,0 +1,368 @@
+/* Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Copyright (C) 2010 Google Inc. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE.WEBKIT file.
+ */
+
+#include <math.h>
+#include "biquad.h"
+
+#ifndef max
+#define max(a, b) ({ __typeof__(a) _a = (a); \
+ __typeof__(b) _b = (b); \
+ _a > _b ? _a : _b; })
+#endif
+
+#ifndef min
+#define min(a, b) ({ __typeof__(a) _a = (a); \
+ __typeof__(b) _b = (b); \
+ _a < _b ? _a : _b; })
+#endif
+
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
+static void set_coefficient(struct biquad *bq, double b0, double b1, double b2,
+ double a0, double a1, double a2)
+{
+ double a0_inv = 1 / a0;
+ bq->b0 = b0 * a0_inv;
+ bq->b1 = b1 * a0_inv;
+ bq->b2 = b2 * a0_inv;
+ bq->a1 = a1 * a0_inv;
+ bq->a2 = a2 * a0_inv;
+}
+
+static void biquad_lowpass(struct biquad *bq, double cutoff, double resonance)
+{
+ /* Limit cutoff to 0 to 1. */
+ cutoff = max(0.0, min(cutoff, 1.0));
+
+ if (cutoff == 1) {
+ /* When cutoff is 1, the z-transform is 1. */
+ set_coefficient(bq, 1, 0, 0, 1, 0, 0);
+ } else if (cutoff > 0) {
+ /* Compute biquad coefficients for lowpass filter */
+ resonance = max(0.0, resonance); /* can't go negative */
+ double g = pow(10.0, 0.05 * resonance);
+ double d = sqrt((4 - sqrt(16 - 16 / (g * g))) / 2);
+
+ double theta = M_PI * cutoff;
+ double sn = 0.5 * d * sin(theta);
+ double beta = 0.5 * (1 - sn) / (1 + sn);
+ double gamma = (0.5 + beta) * cos(theta);
+ double alpha = 0.25 * (0.5 + beta - gamma);
+
+ double b0 = 2 * alpha;
+ double b1 = 2 * 2 * alpha;
+ double b2 = 2 * alpha;
+ double a1 = 2 * -gamma;
+ double a2 = 2 * beta;
+
+ set_coefficient(bq, b0, b1, b2, 1, a1, a2);
+ } else {
+ /* When cutoff is zero, nothing gets through the filter, so set
+ * coefficients up correctly.
+ */
+ set_coefficient(bq, 0, 0, 0, 1, 0, 0);
+ }
+}
+
+static void biquad_highpass(struct biquad *bq, double cutoff, double resonance)
+{
+ /* Limit cutoff to 0 to 1. */
+ cutoff = max(0.0, min(cutoff, 1.0));
+
+ if (cutoff == 1) {
+ /* The z-transform is 0. */
+ set_coefficient(bq, 0, 0, 0, 1, 0, 0);
+ } else if (cutoff > 0) {
+ /* Compute biquad coefficients for highpass filter */
+ resonance = max(0.0, resonance); /* can't go negative */
+ double g = pow(10.0, 0.05 * resonance);
+ double d = sqrt((4 - sqrt(16 - 16 / (g * g))) / 2);
+
+ double theta = M_PI * cutoff;
+ double sn = 0.5 * d * sin(theta);
+ double beta = 0.5 * (1 - sn) / (1 + sn);
+ double gamma = (0.5 + beta) * cos(theta);
+ double alpha = 0.25 * (0.5 + beta + gamma);
+
+ double b0 = 2 * alpha;
+ double b1 = 2 * -2 * alpha;
+ double b2 = 2 * alpha;
+ double a1 = 2 * -gamma;
+ double a2 = 2 * beta;
+
+ set_coefficient(bq, b0, b1, b2, 1, a1, a2);
+ } else {
+ /* When cutoff is zero, we need to be careful because the above
+ * gives a quadratic divided by the same quadratic, with poles
+ * and zeros on the unit circle in the same place. When cutoff
+ * is zero, the z-transform is 1.
+ */
+ set_coefficient(bq, 1, 0, 0, 1, 0, 0);
+ }
+}
+
+static void biquad_bandpass(struct biquad *bq, double frequency, double Q)
+{
+ /* No negative frequencies allowed. */
+ frequency = max(0.0, frequency);
+
+ /* Don't let Q go negative, which causes an unstable filter. */
+ Q = max(0.0, Q);
+
+ if (frequency > 0 && frequency < 1) {
+ double w0 = M_PI * frequency;
+ if (Q > 0) {
+ double alpha = sin(w0) / (2 * Q);
+ double k = cos(w0);
+
+ double b0 = alpha;
+ double b1 = 0;
+ double b2 = -alpha;
+ double a0 = 1 + alpha;
+ double a1 = -2 * k;
+ double a2 = 1 - alpha;
+
+ set_coefficient(bq, b0, b1, b2, a0, a1, a2);
+ } else {
+ /* When Q = 0, the above formulas have problems. If we
+ * look at the z-transform, we can see that the limit
+ * as Q->0 is 1, so set the filter that way.
+ */
+ set_coefficient(bq, 1, 0, 0, 1, 0, 0);
+ }
+ } else {
+ /* When the cutoff is zero, the z-transform approaches 0, if Q
+ * > 0. When both Q and cutoff are zero, the z-transform is
+ * pretty much undefined. What should we do in this case?
+ * For now, just make the filter 0. When the cutoff is 1, the
+ * z-transform also approaches 0.
+ */
+ set_coefficient(bq, 0, 0, 0, 1, 0, 0);
+ }
+}
+
+static void biquad_lowshelf(struct biquad *bq, double frequency, double db_gain)
+{
+ /* Clip frequencies to between 0 and 1, inclusive. */
+ frequency = max(0.0, min(frequency, 1.0));
+
+ double A = pow(10.0, db_gain / 40);
+
+ if (frequency == 1) {
+ /* The z-transform is a constant gain. */
+ set_coefficient(bq, A * A, 0, 0, 1, 0, 0);
+ } else if (frequency > 0) {
+ double w0 = M_PI * frequency;
+ double S = 1; /* filter slope (1 is max value) */
+ double alpha = 0.5 * sin(w0) *
+ sqrt((A + 1 / A) * (1 / S - 1) + 2);
+ double k = cos(w0);
+ double k2 = 2 * sqrt(A) * alpha;
+ double a_plus_one = A + 1;
+ double a_minus_one = A - 1;
+
+ double b0 = A * (a_plus_one - a_minus_one * k + k2);
+ double b1 = 2 * A * (a_minus_one - a_plus_one * k);
+ double b2 = A * (a_plus_one - a_minus_one * k - k2);
+ double a0 = a_plus_one + a_minus_one * k + k2;
+ double a1 = -2 * (a_minus_one + a_plus_one * k);
+ double a2 = a_plus_one + a_minus_one * k - k2;
+
+ set_coefficient(bq, b0, b1, b2, a0, a1, a2);
+ } else {
+ /* When frequency is 0, the z-transform is 1. */
+ set_coefficient(bq, 1, 0, 0, 1, 0, 0);
+ }
+}
+
+static void biquad_highshelf(struct biquad *bq, double frequency,
+ double db_gain)
+{
+ /* Clip frequencies to between 0 and 1, inclusive. */
+ frequency = max(0.0, min(frequency, 1.0));
+
+ double A = pow(10.0, db_gain / 40);
+
+ if (frequency == 1) {
+ /* The z-transform is 1. */
+ set_coefficient(bq, 1, 0, 0, 1, 0, 0);
+ } else if (frequency > 0) {
+ double w0 = M_PI * frequency;
+ double S = 1; /* filter slope (1 is max value) */
+ double alpha = 0.5 * sin(w0) *
+ sqrt((A + 1 / A) * (1 / S - 1) + 2);
+ double k = cos(w0);
+ double k2 = 2 * sqrt(A) * alpha;
+ double a_plus_one = A + 1;
+ double a_minus_one = A - 1;
+
+ double b0 = A * (a_plus_one + a_minus_one * k + k2);
+ double b1 = -2 * A * (a_minus_one + a_plus_one * k);
+ double b2 = A * (a_plus_one + a_minus_one * k - k2);
+ double a0 = a_plus_one - a_minus_one * k + k2;
+ double a1 = 2 * (a_minus_one - a_plus_one * k);
+ double a2 = a_plus_one - a_minus_one * k - k2;
+
+ set_coefficient(bq, b0, b1, b2, a0, a1, a2);
+ } else {
+ /* When frequency = 0, the filter is just a gain, A^2. */
+ set_coefficient(bq, A * A, 0, 0, 1, 0, 0);
+ }
+}
+
+static void biquad_peaking(struct biquad *bq, double frequency, double Q,
+ double db_gain)
+{
+ /* Clip frequencies to between 0 and 1, inclusive. */
+ frequency = max(0.0, min(frequency, 1.0));
+
+ /* Don't let Q go negative, which causes an unstable filter. */
+ Q = max(0.0, Q);
+
+ double A = pow(10.0, db_gain / 40);
+
+ if (frequency > 0 && frequency < 1) {
+ if (Q > 0) {
+ double w0 = M_PI * frequency;
+ double alpha = sin(w0) / (2 * Q);
+ double k = cos(w0);
+
+ double b0 = 1 + alpha * A;
+ double b1 = -2 * k;
+ double b2 = 1 - alpha * A;
+ double a0 = 1 + alpha / A;
+ double a1 = -2 * k;
+ double a2 = 1 - alpha / A;
+
+ set_coefficient(bq, b0, b1, b2, a0, a1, a2);
+ } else {
+ /* When Q = 0, the above formulas have problems. If we
+ * look at the z-transform, we can see that the limit
+ * as Q->0 is A^2, so set the filter that way.
+ */
+ set_coefficient(bq, A * A, 0, 0, 1, 0, 0);
+ }
+ } else {
+ /* When frequency is 0 or 1, the z-transform is 1. */
+ set_coefficient(bq, 1, 0, 0, 1, 0, 0);
+ }
+}
+
+static void biquad_notch(struct biquad *bq, double frequency, double Q)
+{
+ /* Clip frequencies to between 0 and 1, inclusive. */
+ frequency = max(0.0, min(frequency, 1.0));
+
+ /* Don't let Q go negative, which causes an unstable filter. */
+ Q = max(0.0, Q);
+
+ if (frequency > 0 && frequency < 1) {
+ if (Q > 0) {
+ double w0 = M_PI * frequency;
+ double alpha = sin(w0) / (2 * Q);
+ double k = cos(w0);
+
+ double b0 = 1;
+ double b1 = -2 * k;
+ double b2 = 1;
+ double a0 = 1 + alpha;
+ double a1 = -2 * k;
+ double a2 = 1 - alpha;
+
+ set_coefficient(bq, b0, b1, b2, a0, a1, a2);
+ } else {
+ /* When Q = 0, the above formulas have problems. If we
+ * look at the z-transform, we can see that the limit
+ * as Q->0 is 0, so set the filter that way.
+ */
+ set_coefficient(bq, 0, 0, 0, 1, 0, 0);
+ }
+ } else {
+ /* When frequency is 0 or 1, the z-transform is 1. */
+ set_coefficient(bq, 1, 0, 0, 1, 0, 0);
+ }
+}
+
+static void biquad_allpass(struct biquad *bq, double frequency, double Q)
+{
+ /* Clip frequencies to between 0 and 1, inclusive. */
+ frequency = max(0.0, min(frequency, 1.0));
+
+ /* Don't let Q go negative, which causes an unstable filter. */
+ Q = max(0.0, Q);
+
+ if (frequency > 0 && frequency < 1) {
+ if (Q > 0) {
+ double w0 = M_PI * frequency;
+ double alpha = sin(w0) / (2 * Q);
+ double k = cos(w0);
+
+ double b0 = 1 - alpha;
+ double b1 = -2 * k;
+ double b2 = 1 + alpha;
+ double a0 = 1 + alpha;
+ double a1 = -2 * k;
+ double a2 = 1 - alpha;
+
+ set_coefficient(bq, b0, b1, b2, a0, a1, a2);
+ } else {
+ /* When Q = 0, the above formulas have problems. If we
+ * look at the z-transform, we can see that the limit
+ * as Q->0 is -1, so set the filter that way.
+ */
+ set_coefficient(bq, -1, 0, 0, 1, 0, 0);
+ }
+ } else {
+ /* When frequency is 0 or 1, the z-transform is 1. */
+ set_coefficient(bq, 1, 0, 0, 1, 0, 0);
+ }
+}
+
+void biquad_set(struct biquad *bq, enum biquad_type type, double freq, double Q,
+ double gain)
+{
+ /* Default is an identity filter. Also clear history values. */
+ set_coefficient(bq, 1, 0, 0, 1, 0, 0);
+ bq->x1 = 0;
+ bq->x2 = 0;
+ bq->y1 = 0;
+ bq->y2 = 0;
+
+ switch (type) {
+ case BQ_LOWPASS:
+ biquad_lowpass(bq, freq, Q);
+ break;
+ case BQ_HIGHPASS:
+ biquad_highpass(bq, freq, Q);
+ break;
+ case BQ_BANDPASS:
+ biquad_bandpass(bq, freq, Q);
+ break;
+ case BQ_LOWSHELF:
+ biquad_lowshelf(bq, freq, gain);
+ break;
+ case BQ_HIGHSHELF:
+ biquad_highshelf(bq, freq, gain);
+ break;
+ case BQ_PEAKING:
+ biquad_peaking(bq, freq, Q, gain);
+ break;
+ case BQ_NOTCH:
+ biquad_notch(bq, freq, Q);
+ break;
+ case BQ_ALLPASS:
+ biquad_allpass(bq, freq, Q);
+ break;
+ case BQ_NONE:
+ break;
+ }
+}
diff --git a/src/pulsecore/filter/biquad.h b/src/pulsecore/filter/biquad.h
new file mode 100644
index 0000000..c584aa9
--- /dev/null
+++ b/src/pulsecore/filter/biquad.h
@@ -0,0 +1,57 @@
+/* Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef BIQUAD_H_
+#define BIQUAD_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* The biquad filter parameters. The transfer function H(z) is (b0 + b1 * z^(-1)
+ * + b2 * z^(-2)) / (1 + a1 * z^(-1) + a2 * z^(-2)). The previous two inputs
+ * are stored in x1 and x2, and the previous two outputs are stored in y1 and
+ * y2.
+ *
+ * We use double during the coefficients calculation for better accurary, but
+ * float is used during the actual filtering for faster computation.
+ */
+struct biquad {
+ float b0, b1, b2;
+ float a1, a2;
+ float x1, x2;
+ float y1, y2;
+};
+
+/* The type of the biquad filters */
+enum biquad_type {
+ BQ_NONE,
+ BQ_LOWPASS,
+ BQ_HIGHPASS,
+ BQ_BANDPASS,
+ BQ_LOWSHELF,
+ BQ_HIGHSHELF,
+ BQ_PEAKING,
+ BQ_NOTCH,
+ BQ_ALLPASS
+};
+
+/* Initialize a biquad filter parameters from its type and parameters.
+ * Args:
+ * bq - The biquad filter we want to set.
+ * type - The type of the biquad filter.
+ * frequency - The value should be in the range [0, 1]. It is relative to
+ * half of the sampling rate.
+ * Q - Quality factor. See Web Audio API for details.
+ * gain - The value is in dB. See Web Audio API for details.
+ */
+void biquad_set(struct biquad *bq, enum biquad_type type, double freq, double Q,
+ double gain);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* BIQUAD_H_ */
diff --git a/src/pulsecore/filter/crossover.c b/src/pulsecore/filter/crossover.c
new file mode 100644
index 0000000..11a8c6e
--- /dev/null
+++ b/src/pulsecore/filter/crossover.c
@@ -0,0 +1,188 @@
+/* Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "crossover.h"
+#include "biquad.h"
+
+static void lr4_set(struct lr4 *lr4, enum biquad_type type, float freq)
+{
+ struct biquad q;
+ biquad_set(&q, type, freq, 0, 0);
+ lr4->b0 = q.b0;
+ lr4->b1 = q.b1;
+ lr4->b2 = q.b2;
+ lr4->a1 = q.a1;
+ lr4->a2 = q.a2;
+ lr4->x1 = 0;
+ lr4->x2 = 0;
+ lr4->y1 = 0;
+ lr4->y2 = 0;
+ lr4->z1 = 0;
+ lr4->z2 = 0;
+}
+
+/* Split input data using two LR4 filters, put the result into the input array
+ * and another array.
+ *
+ * data0 --+-- lp --> data0
+ * |
+ * \-- hp --> data1
+ */
+static void lr4_split(struct lr4 *lp, struct lr4 *hp, int count, float *data0,
+ float *data1)
+{
+ float lx1 = lp->x1;
+ float lx2 = lp->x2;
+ float ly1 = lp->y1;
+ float ly2 = lp->y2;
+ float lz1 = lp->z1;
+ float lz2 = lp->z2;
+ float lb0 = lp->b0;
+ float lb1 = lp->b1;
+ float lb2 = lp->b2;
+ float la1 = lp->a1;
+ float la2 = lp->a2;
+
+ float hx1 = hp->x1;
+ float hx2 = hp->x2;
+ float hy1 = hp->y1;
+ float hy2 = hp->y2;
+ float hz1 = hp->z1;
+ float hz2 = hp->z2;
+ float hb0 = hp->b0;
+ float hb1 = hp->b1;
+ float hb2 = hp->b2;
+ float ha1 = hp->a1;
+ float ha2 = hp->a2;
+
+ int i;
+ for (i = 0; i < count; i++) {
+ float x, y, z;
+ x = data0[i];
+ y = lb0*x + lb1*lx1 + lb2*lx2 - la1*ly1 - la2*ly2;
+ z = lb0*y + lb1*ly1 + lb2*ly2 - la1*lz1 - la2*lz2;
+ lx2 = lx1;
+ lx1 = x;
+ ly2 = ly1;
+ ly1 = y;
+ lz2 = lz1;
+ lz1 = z;
+ data0[i] = z;
+
+ y = hb0*x + hb1*hx1 + hb2*hx2 - ha1*hy1 - ha2*hy2;
+ z = hb0*y + hb1*hy1 + hb2*hy2 - ha1*hz1 - ha2*hz2;
+ hx2 = hx1;
+ hx1 = x;
+ hy2 = hy1;
+ hy1 = y;
+ hz2 = hz1;
+ hz1 = z;
+ data1[i] = z;
+ }
+
+ lp->x1 = lx1;
+ lp->x2 = lx2;
+ lp->y1 = ly1;
+ lp->y2 = ly2;
+ lp->z1 = lz1;
+ lp->z2 = lz2;
+
+ hp->x1 = hx1;
+ hp->x2 = hx2;
+ hp->y1 = hy1;
+ hp->y2 = hy2;
+ hp->z1 = hz1;
+ hp->z2 = hz2;
+}
+
+/* Split input data using two LR4 filters and sum them back to the original
+ * data array.
+ *
+ * data --+-- lp --+--> data
+ * | |
+ * \-- hp --/
+ */
+static void lr4_merge(struct lr4 *lp, struct lr4 *hp, int count, float *data)
+{
+ float lx1 = lp->x1;
+ float lx2 = lp->x2;
+ float ly1 = lp->y1;
+ float ly2 = lp->y2;
+ float lz1 = lp->z1;
+ float lz2 = lp->z2;
+ float lb0 = lp->b0;
+ float lb1 = lp->b1;
+ float lb2 = lp->b2;
+ float la1 = lp->a1;
+ float la2 = lp->a2;
+
+ float hx1 = hp->x1;
+ float hx2 = hp->x2;
+ float hy1 = hp->y1;
+ float hy2 = hp->y2;
+ float hz1 = hp->z1;
+ float hz2 = hp->z2;
+ float hb0 = hp->b0;
+ float hb1 = hp->b1;
+ float hb2 = hp->b2;
+ float ha1 = hp->a1;
+ float ha2 = hp->a2;
+
+ int i;
+ for (i = 0; i < count; i++) {
+ float x, y, z;
+ x = data[i];
+ y = lb0*x + lb1*lx1 + lb2*lx2 - la1*ly1 - la2*ly2;
+ z = lb0*y + lb1*ly1 + lb2*ly2 - la1*lz1 - la2*lz2;
+ lx2 = lx1;
+ lx1 = x;
+ ly2 = ly1;
+ ly1 = y;
+ lz2 = lz1;
+ lz1 = z;
+
+ y = hb0*x + hb1*hx1 + hb2*hx2 - ha1*hy1 - ha2*hy2;
+ z = hb0*y + hb1*hy1 + hb2*hy2 - ha1*hz1 - ha2*hz2;
+ hx2 = hx1;
+ hx1 = x;
+ hy2 = hy1;
+ hy1 = y;
+ hz2 = hz1;
+ hz1 = z;
+ data[i] = z + lz1;
+ }
+
+ lp->x1 = lx1;
+ lp->x2 = lx2;
+ lp->y1 = ly1;
+ lp->y2 = ly2;
+ lp->z1 = lz1;
+ lp->z2 = lz2;
+
+ hp->x1 = hx1;
+ hp->x2 = hx2;
+ hp->y1 = hy1;
+ hp->y2 = hy2;
+ hp->z1 = hz1;
+ hp->z2 = hz2;
+}
+
+void crossover_init(struct crossover *xo, float freq1, float freq2)
+{
+ int i;
+ for (i = 0; i < 3; i++) {
+ float f = (i == 0) ? freq1 : freq2;
+ lr4_set(&xo->lp[i], BQ_LOWPASS, f);
+ lr4_set(&xo->hp[i], BQ_HIGHPASS, f);
+ }
+}
+
+void crossover_process(struct crossover *xo, int count, float *data0,
+ float *data1, float *data2)
+{
+ lr4_split(&xo->lp[0], &xo->hp[0], count, data0, data1);
+ lr4_merge(&xo->lp[1], &xo->hp[1], count, data0);
+ lr4_split(&xo->lp[2], &xo->hp[2], count, data1, data2);
+}
diff --git a/src/pulsecore/filter/crossover.h b/src/pulsecore/filter/crossover.h
new file mode 100644
index 0000000..99a601c
--- /dev/null
+++ b/src/pulsecore/filter/crossover.h
@@ -0,0 +1,70 @@
+/* Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef CROSSOVER_H_
+#define CROSSOVER_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* An LR4 filter is two biquads with the same parameters connected in series:
+ *
+ * x -- [BIQUAD] -- y -- [BIQUAD] -- z
+ *
+ * Both biquad filter has the same parameter b[012] and a[12],
+ * The variable [xyz][12] keep the history values.
+ */
+struct lr4 {
+ float b0, b1, b2;
+ float a1, a2;
+ float x1, x2;
+ float y1, y2;
+ float z1, z2;
+};
+
+/* Three bands crossover filter:
+ *
+ * INPUT --+-- lp0 --+-- lp1 --+---> LOW (0)
+ * | | |
+ * | \-- hp1 --/
+ * |
+ * \-- hp0 --+-- lp2 ------> MID (1)
+ * |
+ * \-- hp2 ------> HIGH (2)
+ *
+ * [f0] [f1]
+ *
+ * Each lp or hp is an LR4 filter, which consists of two second-order
+ * lowpass or highpass butterworth filters.
+ */
+struct crossover {
+ struct lr4 lp[3], hp[3];
+};
+
+/* Initializes a crossover filter
+ * Args:
+ * xo - The crossover filter we want to initialize.
+ * freq1 - The normalized frequency splits low and mid band.
+ * freq2 - The normalized frequency splits mid and high band.
+ */
+void crossover_init(struct crossover *xo, float freq1, float freq2);
+
+/* Splits input samples to three bands.
+ * Args:
+ * xo - The crossover filter to use.
+ * count - The number of input samples.
+ * data0 - The input samples, also the place to store low band output.
+ * data1 - The place to store mid band output.
+ * data2 - The place to store high band output.
+ */
+void crossover_process(struct crossover *xo, int count, float *data0,
+ float *data1, float *data2);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* CROSSOVER_H_ */
--
1.9.1
