Pass in the Q parameter for setting the filter parameters

Also better handle the peaking filter gain.

2 files changed, 36 insertions, 20 deletions

diff --git a/OpenAL32/Include/alFilter.h b/OpenAL32/Include/alFilter.h
index 9772f432..3c65fd9f 100644
--- a/OpenAL32/Include/alFilter.h
+++ b/OpenAL32/Include/alFilter.h
@@ -3,6 +3,8 @@
 
 #include "alMain.h"
 
+#include "math_defs.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -11,23 +13,29 @@ extern "C" {
 #define HIGHPASSFREQREF  (250.0f)
 
 
-/* Filters implementation is based on the "Cookbook formulae for audio   *
- * EQ biquad filter coefficients" by Robert Bristow-Johnson              *
- * http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt                   */
+/* Filters implementation is based on the "Cookbook formulae for audio
+ * EQ biquad filter coefficients" by Robert Bristow-Johnson
+ * http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
+ */
+/* Implementation note: For the shelf filters, the specified gain is for the
+ * reference frequency, which is the centerpoint of the transition band. This
+ * better matches EFX filter design. To set the gain for the shelf itself, use
+ * the square root of the desired linear gain (or halve the dB gain).
+ */
 
 typedef enum ALfilterType {
     /** EFX-style low-pass filter, specifying a gain and reference frequency. */
     ALfilterType_HighShelf,
     /** EFX-style high-pass filter, specifying a gain and reference frequency. */
     ALfilterType_LowShelf,
-    /** Peaking filter, specifying a gain, reference frequency, and bandwidth. */
+    /** Peaking filter, specifying a gain and reference frequency. */
     ALfilterType_Peaking,
 
-    /** Low-pass cut-off filter, specifying a cut-off frequency and bandwidth. */
+    /** Low-pass cut-off filter, specifying a cut-off frequency. */
     ALfilterType_LowPass,
-    /** High-pass cut-off filter, specifying a cut-off frequency and bandwidth. */
+    /** High-pass cut-off filter, specifying a cut-off frequency. */
     ALfilterType_HighPass,
-    /** Band-pass filter, specifying a center frequency and bandwidth. */
+    /** Band-pass filter, specifying a center frequency. */
     ALfilterType_BandPass,
 } ALfilterType;
 
@@ -41,8 +49,27 @@ typedef struct ALfilterState {
 } ALfilterState;
 #define ALfilterState_process(a, ...) ((a)->process((a), __VA_ARGS__))
 
+/* Calculates the rcpQ (i.e. 1/Q) coefficient for shelving filters, using the
+ * reference gain and shelf slope parameter.
+ * 0 < gain
+ * 0 < slope <= 1
+ */
+inline ALfloat calc_rcpQ_from_slope(ALfloat gain, ALfloat slope)
+{
+    return sqrtf((gain + 1.0f/gain)*(1.0f/slope - 1.0f) + 2.0f);
+}
+/* Calculates the rcpQ (i.e. 1/Q) coefficient for filters, using the frequency
+ * multiple (i.e. ref_freq / sampling_freq) and bandwidth.
+ * 0 < freq_mult < 0.5.
+ */
+inline ALfloat calc_rcpQ_from_bandwidth(ALfloat freq_mult, ALfloat bandwidth)
+{
+    ALfloat w0 = F_TAU * freq_mult;
+    return 2.0f*sinhf(logf(2.0f)/2.0f*bandwidth*w0/sinf(w0));
+}
+
 void ALfilterState_clear(ALfilterState *filter);
-void ALfilterState_setParams(ALfilterState *filter, ALfilterType type, ALfloat gain, ALfloat freq_mult, ALfloat bandwidth);
+void ALfilterState_setParams(ALfilterState *filter, ALfilterType type, ALfloat gain, ALfloat freq_mult, ALfloat rcpQ);
 
 inline ALfloat ALfilterState_processSingle(ALfilterState *filter, ALfloat sample)
 {
diff --git a/OpenAL32/Include/alu.h b/OpenAL32/Include/alu.h
index 126fffb5..27cf6713 100644
--- a/OpenAL32/Include/alu.h
+++ b/OpenAL32/Include/alu.h
@@ -16,18 +16,7 @@
 
 #include "hrtf.h"
 #include "align.h"
-
-
-#define F_PI    (3.14159265358979323846f)
-#define F_PI_2  (1.57079632679489661923f)
-#define F_TAU   (6.28318530717958647692f)
-
-#ifndef FLT_EPSILON
-#define FLT_EPSILON (1.19209290e-07f)
-#endif
-
-#define DEG2RAD(x)  ((ALfloat)(x) * (F_PI/180.0f))
-#define RAD2DEG(x)  ((ALfloat)(x) * (180.0f/F_PI))
+#include "math_defs.h"
 
 
 #define MAX_PITCH  (255)