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authorChris Robinson <[email protected]>2010-04-08 09:36:20 -0700
committerChris Robinson <[email protected]>2010-04-08 09:36:20 -0700
commit76f8c1e4e212e23133406691babb5dddc2b81dad (patch)
treeb08afd48ba5fd0ac00aa27829e2d1ca0f168be91
parentb273d616ad5a9979cbf0b69318aded6ec821450e (diff)
Implement a basic high-pass cutoff filter in the ring modulator
-rw-r--r--Alc/alcModulator.c34
1 files changed, 28 insertions, 6 deletions
diff --git a/Alc/alcModulator.c b/Alc/alcModulator.c
index 558e861b..b20cabaf 100644
--- a/Alc/alcModulator.c
+++ b/Alc/alcModulator.c
@@ -33,8 +33,25 @@
typedef struct ALmodulatorState {
// Must be first in all effects!
ALeffectState state;
+
+ FILTER iirFilter;
+ ALfloat history[1];
} ALmodulatorState;
+
+static __inline ALfloat hpFilter1P(FILTER *iir, ALuint offset, ALfloat input)
+{
+ ALfloat *history = &iir->history[offset];
+ ALfloat a = iir->coeff;
+ ALfloat output = input;
+
+ output = output + (history[0]-output)*a;
+ history[0] = output;
+
+ return input - output;
+}
+
+
static ALvoid ModulatorDestroy(ALeffectState *effect)
{
ALmodulatorState *state = (ALmodulatorState*)effect;
@@ -44,15 +61,18 @@ static ALvoid ModulatorDestroy(ALeffectState *effect)
static ALboolean ModulatorDeviceUpdate(ALeffectState *effect, ALCdevice *Device)
{
return AL_TRUE;
- (void)Device;
(void)effect;
+ (void)Device;
}
static ALvoid ModulatorUpdate(ALeffectState *effect, ALCcontext *Context, const ALeffect *Effect)
{
- (void)effect;
- (void)Context;
- (void)Effect;
+ ALmodulatorState *state = (ALmodulatorState*)effect;
+ ALfloat cw, a = 0.0f;
+
+ cw = cos(2.0*M_PI * Effect->Modulator.HighPassCutoff / Context->Device->Frequency);
+ a = (2.0f-cw) - aluSqrt(aluPow(2.0f-cw, 2.0f) - 1.0f);
+ state->iirFilter.coeff = a;
}
static ALvoid ModulatorProcess(ALeffectState *effect, const ALeffectslot *Slot, ALuint SamplesToDo, const ALfloat *SamplesIn, ALfloat (*SamplesOut)[OUTPUTCHANNELS])
@@ -61,11 +81,10 @@ static ALvoid ModulatorProcess(ALeffectState *effect, const ALeffectslot *Slot,
const ALfloat gain = Slot->Gain;
ALfloat samp;
ALuint i;
- (void)state;
for(i = 0;i < SamplesToDo;i++)
{
- samp = SamplesIn[i];
+ samp = hpFilter1P(&state->iirFilter, 0, SamplesIn[i]);
// Apply slot gain
samp *= gain;
@@ -92,5 +111,8 @@ ALeffectState *ModulatorCreate(void)
state->state.Update = ModulatorUpdate;
state->state.Process = ModulatorProcess;
+ state->iirFilter.coeff = 0.0f;
+ state->iirFilter.history[0] = 0.0f;
+
return &state->state;
}