1 files changed, 57 insertions, 0 deletions
diff --git a/src/pulsecore/filter/biquad.h b/src/pulsecore/filter/biquad.h
new file mode 100644
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+++ 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_ */