Use the high-shelf filter in place of low-pass

They effectively both work to lower (or raise) high frequencies. However, the
high-shelf performs better when gain=1.

5 files changed, 6 insertions, 19 deletions

diff --git a/Alc/ALu.c b/Alc/ALu.c
index 57dfa30f..c05fb48c 100644
--- a/Alc/ALu.c
+++ b/Alc/ALu.c
@@ -455,7 +455,7 @@ ALvoid CalcNonAttnSourceParams(ALsource *ALSource, const ALCcontext *ALContext)
         ALfloat gain = maxf(0.001f, sqrtf(DryGainHF));
         for(c = 0;c < num_channels;c++)
             ALfilterState_setParams(&ALSource->Params.Direct.Filter[c],
-                                    ALfilterType_LowPass, gain,
+                                    ALfilterType_HighShelf, gain,
                                     (ALfloat)LOWPASSFREQREF/Frequency, 0.0f);
     }
     for(i = 0;i < NumSends;i++)
@@ -463,7 +463,7 @@ ALvoid CalcNonAttnSourceParams(ALsource *ALSource, const ALCcontext *ALContext)
         ALfloat gain = maxf(0.001f, sqrtf(WetGainHF[i]));
         for(c = 0;c < num_channels;c++)
             ALfilterState_setParams(&ALSource->Params.Send[i].Filter[c],
-                                    ALfilterType_LowPass, gain,
+                                    ALfilterType_HighShelf, gain,
                                     (ALfloat)LOWPASSFREQREF/Frequency, 0.0f);
     }
 }
@@ -904,14 +904,14 @@ ALvoid CalcSourceParams(ALsource *ALSource, const ALCcontext *ALContext)
     {
         ALfloat gain = maxf(0.001f, sqrtf(DryGainHF));
         ALfilterState_setParams(&ALSource->Params.Direct.Filter[0],
-                                ALfilterType_LowPass, gain,
+                                ALfilterType_HighShelf, gain,
                                 (ALfloat)LOWPASSFREQREF/Frequency, 0.0f);
     }
     for(i = 0;i < NumSends;i++)
     {
         ALfloat gain = maxf(0.001f, sqrtf(WetGainHF[i]));
         ALfilterState_setParams(&ALSource->Params.Send[i].Filter[0],
-                                ALfilterType_LowPass, gain,
+                                ALfilterType_HighShelf, gain,
                                 (ALfloat)LOWPASSFREQREF/Frequency, 0.0f);
     }
 }
diff --git a/Alc/effects/echo.c b/Alc/effects/echo.c
index a45f3398..9d17ead0 100644
--- a/Alc/effects/echo.c
+++ b/Alc/effects/echo.c
@@ -104,7 +104,7 @@ static ALvoid ALechoState_Update(ALechoState *state, ALCdevice *Device, const AL
 
     state->FeedGain = Slot->EffectProps.Echo.Feedback;
 
-    ALfilterState_setParams(&state->Filter, ALfilterType_LowPass,
+    ALfilterState_setParams(&state->Filter, ALfilterType_HighShelf,
                             1.0f - Slot->EffectProps.Echo.Damping,
                             (ALfloat)LOWPASSFREQREF/frequency, 0.0f);
 
diff --git a/Alc/effects/reverb.c b/Alc/effects/reverb.c
index 5d85ee7b..74f2368c 100644
--- a/Alc/effects/reverb.c
+++ b/Alc/effects/reverb.c
@@ -1095,7 +1095,7 @@ static ALvoid ALreverbState_Update(ALreverbState *State, ALCdevice *Device, cons
         freq_scale = Slot->EffectProps.Reverb.HFReference / frequency;
     else
         freq_scale = (ALfloat)LOWPASSFREQREF / frequency;
-    ALfilterState_setParams(&State->LpFilter, ALfilterType_LowPass,
+    ALfilterState_setParams(&State->LpFilter, ALfilterType_HighShelf,
                             Slot->EffectProps.Reverb.GainHF,
                             freq_scale, 0.0f);
 
diff --git a/OpenAL32/Include/alFilter.h b/OpenAL32/Include/alFilter.h
index dd5edbb9..f42747f2 100644
--- a/OpenAL32/Include/alFilter.h
+++ b/OpenAL32/Include/alFilter.h
@@ -16,8 +16,6 @@ ALfloat lpCoeffCalc(ALfloat g, ALfloat cw);
 
 
 typedef enum ALfilterType {
-    ALfilterType_LowPass,
-
     ALfilterType_HighShelf,
     ALfilterType_LowShelf,
     ALfilterType_Peaking,
diff --git a/OpenAL32/alFilter.c b/OpenAL32/alFilter.c
index 550c99f5..5bef87fd 100644
--- a/OpenAL32/alFilter.c
+++ b/OpenAL32/alFilter.c
@@ -343,17 +343,6 @@ void ALfilterState_setParams(ALfilterState *filter, ALfilterType type, ALfloat g
     /* Calculate filter coefficients depending on filter type */
     switch(type)
     {
-        case ALfilterType_LowPass:
-            alpha = sinf(w0) / 2.0f * sqrtf((gain + 1.0f/gain) *
-                                            (1.0f/0.75f - 1.0f) + 2.0f);
-            filter->b[0] = (1.0f - cosf(w0)) * 0.5f;
-            filter->b[1] =  1.0f - cosf(w0);
-            filter->b[2] = (1.0f - cosf(w0)) * 0.5f;
-            filter->a[0] =  1.0f + alpha;
-            filter->a[1] = -2.0f*cosf(w0);
-            filter->a[2] =  1.0f - alpha;
-            break;
-
         case ALfilterType_HighShelf:
             alpha = sinf(w0) / 2.0f * sqrtf((gain + 1.0f/gain) *
                                             (1.0f/0.75f - 1.0f) + 2.0f);