Add experimental code for biquad and low-pass filters.

research/ma_lpf.h

@@ -0,0 +1,237 @@
+#ifndef ma_lpf_h
+#define ma_lpf_h
+
+/*
+TODO:
+  - Document passthrough behaviour of the biquad filter and how it doesn't update previous inputs and outputs.
+  - Document how changing biquad constants requires reinitialization of the filter (due to issue above).
+*/
+
+typedef struct
+{
+    ma_format format;
+    ma_uint32 channels;
+    float a0;
+    float a1;
+    float a2;
+    float b0;
+    float b1;
+    float b2;
+} ma_biquad_config;
+
+ma_biquad_config ma_biquad_config_init(ma_format format, ma_uint32 channels, float a0, float a1, float a2, float b0, float b1, float b2);
+
+typedef struct
+{
+    ma_biquad_config config;
+    ma_bool32 isPassthrough;
+    ma_uint32 prevFrameCount;
+    float x1[MA_MAX_CHANNELS];   /* x[n-1] */
+    float x2[MA_MAX_CHANNELS];   /* x[n-2] */
+    float y1[MA_MAX_CHANNELS];   /* y[n-1] */
+    float y2[MA_MAX_CHANNELS];   /* y[n-2] */
+} ma_biquad;
+
+ma_result ma_biquad_init(const ma_biquad_config* pConfig, ma_biquad* pBQ);
+ma_result ma_biquad_process(ma_biquad* pBQ, void* pFramesOut, const void* pFramesIn, ma_uint64 frameCount);
+
+
+typedef struct
+{
+    ma_format format;
+    ma_uint32 channels;
+    ma_uint32 sampleRate;
+    ma_uint32 cutoffFrequency;
+} ma_lpf_config;
+
+ma_lpf_config ma_lpf_config_init(ma_format format, ma_uint32 channels, ma_uint32 sampleRate, ma_uint32 cutoffFrequency);
+
+typedef struct
+{
+    ma_biquad bq;   /* The low-pass filter is implemented as a biquad filter. */
+    ma_lpf_config config;
+} ma_lpf;
+
+ma_result ma_lpf_init(const ma_lpf_config* pConfig, ma_lpf* pLPF);
+ma_result ma_lpf_process(ma_lpf* pLPF, void* pFramesOut, const void* pFramesIn, ma_uint64 frameCount);
+
+#endif  /* ma_lpf_h */
+
+
+
+
+#if defined(MINIAUDIO_IMPLEMENTATION)
+
+ma_biquad_config ma_biquad_config_init(ma_format format, ma_uint32 channels, float a0, float a1, float a2, float b0, float b1, float b2)
+{
+    ma_biquad_config config;
+
+    MA_ZERO_OBJECT(&config);
+    config.format = format;
+    config.channels = channels;
+    config.a0 = a0;
+    config.a1 = a1;
+    config.a2 = a2;
+    config.b0 = b0;
+    config.b1 = b1;
+    config.b2 = b2;
+
+    return config;
+}
+
+ma_result ma_biquad_init(const ma_biquad_config* pConfig, ma_biquad* pBQ)
+{
+    if (pBQ == NULL) {
+        return MA_INVALID_ARGS;
+    }
+
+    MA_ZERO_OBJECT(pBQ);
+
+    if (pConfig == NULL) {
+        return MA_INVALID_ARGS;
+    }
+
+    if (pConfig->a0 == 0) {
+        return MA_INVALID_ARGS; /* Division by zero. */
+    }
+
+    /* Currently only supporting f32, but support for other formats will be added later. */
+    if (pConfig->format != ma_format_f32) {
+        return MA_INVALID_ARGS;
+    }
+
+    pBQ->config = *pConfig;
+
+    if (pConfig->a0 == 1 && pConfig->a1 == 0 && pConfig->a2 == 0 &&
+        pConfig->b0 == 1 && pConfig->b1 == 0 && pConfig->b2 == 0) {
+        pBQ->isPassthrough = MA_TRUE;
+    }
+
+    /* Normalize. */
+    pBQ->config.a1 /= pBQ->config.a0;
+    pBQ->config.a2 /= pBQ->config.a0;
+    pBQ->config.b0 /= pBQ->config.a0;
+    pBQ->config.b1 /= pBQ->config.a0;
+    pBQ->config.b2 /= pBQ->config.a0;
+
+    return MA_SUCCESS;
+}
+
+ma_result ma_biquad_process(ma_biquad* pBQ, void* pFramesOut, const void* pFramesIn, ma_uint64 frameCount)
+{
+    ma_uint32 n;
+    ma_uint32 c;
+    float a1 = pBQ->config.a1;
+    float a2 = pBQ->config.a2;
+    float b0 = pBQ->config.b0;
+    float b1 = pBQ->config.b1;
+    float b2 = pBQ->config.b2;
+
+    if (pBQ == NULL || pFramesOut == NULL || pFramesIn == NULL) {
+        return MA_INVALID_ARGS;
+    }
+
+    /* Fast path for passthrough. */
+    if (pBQ->isPassthrough) {
+        ma_copy_memory_64(pFramesOut, pFramesIn, frameCount * ma_get_bytes_per_frame(pBQ->config.format, pBQ->config.channels));
+        return MA_SUCCESS;
+    }
+
+    /* Currently only supporting f32. */
+    if (pBQ->config.format == ma_format_f32) {
+              float* pY = (      float*)pFramesOut;
+        const float* pX = (const float*)pFramesIn;
+
+        for (n = 0; n < frameCount; n += 1) {
+            for (c = 0; c < pBQ->config.channels; c += 1) {
+                float x2 = pBQ->x2[c];
+                float x1 = pBQ->x1[c];
+                float x0 = pX[n*pBQ->config.channels + c];
+                float y2 = pBQ->y2[c];
+                float y1 = pBQ->y1[c];
+                float y0 = b0*x0 + b1*x1 + b2*x2 - a1*y1 - a2*y2;
+                
+                pY[n*pBQ->config.channels + c] = y0;
+                pBQ->x2[c] = x1;
+                pBQ->x1[c] = x0;
+                pBQ->y2[c] = y1;
+                pBQ->y1[c] = y0;
+            }
+        }
+    } else {
+        return MA_INVALID_ARGS; /* Format not supported. Should never hit this because it's checked in ma_biquad_init(). */
+    }
+
+    return MA_SUCCESS;
+}
+
+
+ma_lpf_config ma_lpf_config_init(ma_format format, ma_uint32 channels, ma_uint32 sampleRate, ma_uint32 cutoffFrequency)
+{
+    ma_lpf_config config;
+    
+    MA_ZERO_OBJECT(&config);
+    config.format = format;
+    config.channels = channels;
+    config.sampleRate = sampleRate;
+    config.cutoffFrequency = cutoffFrequency;
+
+    return config;
+}
+
+ma_result ma_lpf_init(const ma_lpf_config* pConfig, ma_lpf* pLPF)
+{
+    ma_result result;
+    ma_biquad_config bqConfig;
+    double q;
+    double w;
+    double s;
+    double c;
+    double a;
+
+    if (pLPF == NULL) {
+        return MA_INVALID_ARGS;
+    }
+
+    MA_ZERO_OBJECT(pLPF);
+
+    if (pConfig == NULL) {
+        return MA_INVALID_ARGS;
+    }
+
+    pLPF->config = *pConfig;
+
+    q = 1 / sqrt(2);
+    w = 2 * MA_PI_D * pConfig->cutoffFrequency / pConfig->sampleRate;
+    s = sin(w);
+    c = cos(w);
+    a = s / (2*q);
+
+    bqConfig.a0 = (float)( 1 + a);
+    bqConfig.a1 = (float)(-2 * c);
+    bqConfig.a2 = (float)( 1 - a);
+    bqConfig.b0 = (float)((1 - c) / 2);
+    bqConfig.b1 = (float)( 1 - c);
+    bqConfig.b2 = (float)((1 - c) / 2);
+
+    bqConfig.format = pConfig->format;
+    bqConfig.channels = pConfig->channels;
+
+    result = ma_biquad_init(&bqConfig, &pLPF->bq);
+    if (result != MA_SUCCESS) {
+        return result;
+    }
+
+    return MA_SUCCESS;
+}
+
+ma_result ma_lpf_process(ma_lpf* pLPF, void* pFramesOut, const void* pFramesIn, ma_uint64 frameCount)
+{
+    if (pLPF == NULL) {
+        return MA_INVALID_ARGS;
+    }
+
+    return ma_biquad_process(&pLPF->bq, pFramesOut, pFramesIn, frameCount);
+}
+
+#endif

research/ma_resampler.h

@@ -3,49 +3,43 @@
 #ifndef ma_resampler_h
 #define ma_resampler_h
 
+#include "ma_lpf.h"
+
 typedef enum
 {
-    ma_resample_algorithm_linear = 0,   /* Fastest, lowest quality. */
-    ma_resample_algorithm_linear_lpf,   /* Linear with a biquad low pass filter. */
+    ma_resample_algorithm_linear_lpf = 0,   /* Linear with a biquad low pass filter. Default. */
+    ma_resample_algorithm_linear,           /* Fastest, lowest quality. */
 } ma_resample_algorithm;
 
 typedef struct
 {
-    ma_resample_algorithm algorithm;
+    ma_format format;   /* Must be either ma_format_f32 or ma_format_s16. */
+    ma_uint32 channels;
     ma_uint32 sampleRateIn;
     ma_uint32 sampleRateOut;
-    ma_uint32 channels;
-    ma_format format;   /* Must be either ma_format_f32 or ma_format_s16. */
+    ma_resample_algorithm algorithm;
     struct
     {
         int _unused;
     } linear;
     struct
     {
-        int _unused;
+        ma_uint32 cutoffFrequency;
     } linearLPF;
 } ma_resampler_config;
 
+ma_resampler_config ma_resampler_config_init(ma_format format, ma_uint32 channels, ma_uint32 sampleRateIn, ma_uint32 sampleRateOut, ma_resample_algorithm algorithm);
+
 typedef struct
 {
     ma_resampler_config config;
+    float timeX;    /* Input time. */
+    float timeY;    /* Output time. */
     union
     {
         struct
         {
-            float timeX;    /* Input time. */
-            float timeY;    /* Output time. */
-            struct
-            {
-                float yprev1;   /* y-1 */
-                float yprev2;   /* y-2 */
-                float a0;
-                float a1;
-                float a2;
-                float b0;
-                float b1;
-                float b2;
-            } lpf;
+            ma_lpf lpf;
         } linear;
     } state;
 } ma_resampler;
@@ -75,7 +69,7 @@ It is an error for [pFramesOut] to be non-NULL and [pFrameCountOut] to be NULL.
 
 It is an error for both [pFrameCountOut] and [pFrameCountIn] to be NULL.
 */
-ma_result ma_resampler_process(ma_resampler* pResampler, ma_uint64* pFrameCountOut, void* pFramesOut, ma_uint64* pFrameCountIn, void* pFramesIn);
+ma_result ma_resampler_process(ma_resampler* pResampler, ma_uint64* pFrameCountOut, void* pFramesOut, ma_uint64* pFrameCountIn, const void* pFramesIn);
 
 
 /*
@@ -99,37 +93,52 @@ Implementation
 #define MA_RESAMPLER_MAX_RATIO 48.0
 #endif
 
+ma_resampler_config ma_resampler_config_init(ma_format format, ma_uint32 channels, ma_uint32 sampleRateIn, ma_uint32 sampleRateOut, ma_resample_algorithm algorithm)
+{
+    ma_resampler_config config;
+
+    MA_ZERO_OBJECT(&config);
+    config.format = format;
+    config.channels = channels;
+    config.sampleRateIn = sampleRateIn;
+    config.sampleRateOut = sampleRateOut;
+    config.algorithm = algorithm;
+
+    return config;
+}
+
 ma_result ma_resampler_init(const ma_resampler_config* pConfig, ma_resampler* pResampler)
 {
+    ma_result result;
+
     if (pConfig == NULL || pResampler == NULL) {
         return MA_INVALID_ARGS;
     }
 
     MA_ZERO_OBJECT(pResampler);
     pResampler->config = *pConfig;
+    pResampler->timeX = 0.0f;
+    pResampler->timeY = 0.0f;
 
     switch (pConfig->algorithm)
     {
         case ma_resample_algorithm_linear:
         {
-            pResampler->state.linear.timeX = 0.0f;
-            pResampler->state.linear.timeY = 0.0f;
         } break;
 
         case ma_resample_algorithm_linear_lpf:
         {
-            pResampler->state.linear.timeX = 0.0f;
-            pResampler->state.linear.timeY = 0.0f;
-            pResampler->state.linear.lpf.yprev1 = 0.0f;
-            pResampler->state.linear.lpf.yprev2 = 0.0f;
+            ma_lpf_config lpfConfig;
+            
+            lpfConfig = ma_lpf_config_init(pConfig->format, pConfig->channels, pConfig->sampleRateOut, pConfig->linearLPF.cutoffFrequency);
+            if (lpfConfig.cutoffFrequency == 0) {
+                lpfConfig.cutoffFrequency = ma_min(pConfig->sampleRateIn, pConfig->sampleRateOut) / 2;
+            }
 
-            /* TODO: Biquad LPF filter coefficients. */
-            pResampler->state.linear.lpf.a0 = 0.0f;
-            pResampler->state.linear.lpf.a1 = 0.0f;
-            pResampler->state.linear.lpf.a2 = 0.0f;
-            pResampler->state.linear.lpf.b0 = 0.0f;
-            pResampler->state.linear.lpf.b1 = 0.0f;
-            pResampler->state.linear.lpf.b2 = 0.0f;
+            result = ma_lpf_init(&lpfConfig, &pResampler->state.linear.lpf);
+            if (result != MA_SUCCESS) {
+                return result;
+            }
         } break;
 
         default: return MA_INVALID_ARGS;
@@ -138,7 +147,7 @@ ma_result ma_resampler_init(const ma_resampler_config* pConfig, ma_resampler* pR
     return MA_SUCCESS;
 }
 
-static ma_result ma_resampler_process__seek__linear(ma_resampler* pResampler, ma_uint64* pFrameCountOut, ma_uint64* pFrameCountIn, void* pFramesIn)
+static ma_result ma_resampler_process__seek__linear(ma_resampler* pResampler, ma_uint64* pFrameCountOut, ma_uint64* pFrameCountIn, const void* pFramesIn)
 {
     MA_ASSERT(pResampler != NULL);
 
@@ -163,13 +172,13 @@ static ma_result ma_resampler_process__seek__linear(ma_resampler* pResampler, ma
     return MA_SUCCESS;
 }
 
-static ma_result ma_resampler_process__seek__linear_lpf(ma_resampler* pResampler, ma_uint64* pFrameCountOut, ma_uint64* pFrameCountIn, void* pFramesIn)
+static ma_result ma_resampler_process__seek__linear_lpf(ma_resampler* pResampler, ma_uint64* pFrameCountOut, ma_uint64* pFrameCountIn, const void* pFramesIn)
 {
     /* TODO: Proper linear LPF implementation. */
     return ma_resampler_process__seek__linear(pResampler, pFrameCountOut, pFrameCountIn, pFramesIn);
 }
 
-static ma_result ma_resampler_process__seek(ma_resampler* pResampler, ma_uint64* pFrameCountOut, ma_uint64* pFrameCountIn, void* pFramesIn)
+static ma_result ma_resampler_process__seek(ma_resampler* pResampler, ma_uint64* pFrameCountOut, ma_uint64* pFrameCountIn, const void* pFramesIn)
 {
     MA_ASSERT(pResampler != NULL);
 
@@ -190,7 +199,7 @@ static ma_result ma_resampler_process__seek(ma_resampler* pResampler, ma_uint64*
 }
 
 
-static ma_result ma_resampler_process__read__linear(ma_resampler* pResampler, ma_uint64* pFrameCountOut, void* pFramesOut, ma_uint64* pFrameCountIn, void* pFramesIn)
+static ma_result ma_resampler_process__read__linear(ma_resampler* pResampler, ma_uint64* pFrameCountOut, void* pFramesOut, ma_uint64* pFrameCountIn, const void* pFramesIn)
 {
     MA_ASSERT(pResampler     != NULL);
     MA_ASSERT(pFramesOut     != NULL);
@@ -205,13 +214,13 @@ static ma_result ma_resampler_process__read__linear(ma_resampler* pResampler, ma
     return MA_SUCCESS;
 }
 
-static ma_result ma_resampler_process__read__linear_lpf(ma_resampler* pResampler, ma_uint64* pFrameCountOut, void* pFramesOut, ma_uint64* pFrameCountIn, void* pFramesIn)
+static ma_result ma_resampler_process__read__linear_lpf(ma_resampler* pResampler, ma_uint64* pFrameCountOut, void* pFramesOut, ma_uint64* pFrameCountIn, const void* pFramesIn)
 {
     /* TODO: Proper linear LPF implementation. */
     return ma_resampler_process__read__linear(pResampler, pFrameCountOut, pFramesOut, pFrameCountIn, pFramesIn);
 }
 
-static ma_result ma_resampler_process__read(ma_resampler* pResampler, ma_uint64* pFrameCountOut, void* pFramesOut, ma_uint64* pFrameCountIn, void* pFramesIn)
+static ma_result ma_resampler_process__read(ma_resampler* pResampler, ma_uint64* pFrameCountOut, void* pFramesOut, ma_uint64* pFrameCountIn, const void* pFramesIn)
 {
     MA_ASSERT(pResampler != NULL);
     MA_ASSERT(pFramesOut != NULL);
@@ -237,13 +246,13 @@ static ma_result ma_resampler_process__read(ma_resampler* pResampler, ma_uint64*
     }
 }
 
-ma_result ma_resampler_process(ma_resampler* pResampler, ma_uint64* pFrameCountOut, void* pFramesOut, ma_uint64* pFrameCountIn, void* pFramesIn)
+ma_result ma_resampler_process(ma_resampler* pResampler, ma_uint64* pFrameCountOut, void* pFramesOut, ma_uint64* pFrameCountIn, const void* pFramesIn)
 {
     if (pResampler == NULL) {
         return MA_INVALID_ARGS;
     }
 
-    if (pFrameCountOut != NULL && pFrameCountIn == NULL) {
+    if (pFrameCountOut == NULL && pFrameCountIn == NULL) {
         return MA_INVALID_ARGS;
     }
 

research/tests/ma_lpf_test_0.c

@@ -0,0 +1,109 @@
+#define DR_FLAC_IMPLEMENTATION
+#include "../../extras/dr_flac.h"  /* Enables FLAC decoding. */
+#define DR_MP3_IMPLEMENTATION
+#include "../../extras/dr_mp3.h"   /* Enables MP3 decoding. */
+#define DR_WAV_IMPLEMENTATION
+#include "../../extras/dr_wav.h"   /* Enables WAV decoding. */
+
+
+#define MA_DEBUG_OUTPUT
+#define MINIAUDIO_IMPLEMENTATION
+#include "../../miniaudio.h"
+#include "../ma_lpf.h"
+
+ma_lpf g_lpf;
+
+void data_callback(ma_device* pDevice, void* pOutput, const void* pInput, ma_uint32 frameCount)
+{
+    ma_uint32 framesProcessed = 0;
+    ma_decoder* pDecoder = (ma_decoder*)pDevice->pUserData;
+    if (pDecoder == NULL) {
+        return;
+    }
+
+    /* We need to read into a temporary buffer and then run it through the low pass filter. */
+    while (framesProcessed < frameCount) {
+        float tempBuffer[4096];
+        ma_uint32 framesToProcessThisIteration;
+
+        framesToProcessThisIteration = frameCount - framesProcessed;
+        if (framesToProcessThisIteration > ma_countof(tempBuffer)/pDecoder->internalChannels) {
+            framesToProcessThisIteration = ma_countof(tempBuffer)/pDecoder->internalChannels;
+        }
+
+    #if 0
+        ma_decoder_read_pcm_frames(pDecoder, ma_offset_ptr(pOutput, framesProcessed * ma_get_bytes_per_frame(pDevice->playback.format, pDevice->playback.channels)), framesToProcessThisIteration);
+    #else
+        ma_decoder_read_pcm_frames(pDecoder, tempBuffer, framesToProcessThisIteration);
+
+        /* Out the results from the low pass filter straight into our output buffer. */
+        ma_lpf_process(&g_lpf, ma_offset_ptr(pOutput, framesProcessed * ma_get_bytes_per_frame(pDevice->playback.format, pDevice->playback.channels)), tempBuffer, framesToProcessThisIteration);
+    #endif
+
+        framesProcessed += framesToProcessThisIteration;
+    }
+
+    (void)pInput;
+}
+
+int main(int argc, char** argv)
+{
+    ma_result result;
+    ma_decoder_config decoderConfig;
+    ma_decoder decoder;
+    ma_lpf_config lpfConfig;
+    ma_device_config deviceConfig;
+    ma_device device;
+
+    if (argc < 2) {
+        printf("No input file.\n");
+        return -1;
+    }
+
+    decoderConfig = ma_decoder_config_init(ma_format_f32, 0, 0);
+
+    result = ma_decoder_init_file(argv[1], &decoderConfig, &decoder);
+    if (result != MA_SUCCESS) {
+        return -2;
+    }
+
+
+    lpfConfig.format          = decoderConfig.format;
+    lpfConfig.channels        = decoder.internalChannels;
+    lpfConfig.sampleRate      = decoder.internalSampleRate;
+    lpfConfig.cutoffFrequency = lpfConfig.sampleRate / 4;
+
+    result = ma_lpf_init(&lpfConfig, &g_lpf);
+    if (result != MA_SUCCESS) {
+        return -100;
+    }
+
+
+    deviceConfig = ma_device_config_init(ma_device_type_playback);
+    deviceConfig.playback.format   = decoder.outputFormat;
+    deviceConfig.playback.channels = decoder.outputChannels;
+    deviceConfig.sampleRate        = decoder.outputSampleRate;
+    deviceConfig.dataCallback      = data_callback;
+    deviceConfig.pUserData         = &decoder;
+
+    if (ma_device_init(NULL, &deviceConfig, &device) != MA_SUCCESS) {
+        printf("Failed to open playback device.\n");
+        ma_decoder_uninit(&decoder);
+        return -3;
+    }
+
+    if (ma_device_start(&device) != MA_SUCCESS) {
+        printf("Failed to start playback device.\n");
+        ma_device_uninit(&device);
+        ma_decoder_uninit(&decoder);
+        return -4;
+    }
+
+    printf("Press Enter to quit...");
+    getchar();
+
+    ma_device_uninit(&device);
+    ma_decoder_uninit(&decoder);
+
+    return 0;
+}

tests/ma_test_0.vcxproj

@@ -327,13 +327,14 @@
       <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Release|x64'">true</ExcludedFromBuild>
     </ClCompile>
     <ClCompile Include="..\examples\simple_playback_emscripten.c">
-      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">false</ExcludedFromBuild>
-      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">false</ExcludedFromBuild>
-      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Debug|ARM'">false</ExcludedFromBuild>
-      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Release|ARM'">false</ExcludedFromBuild>
-      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">false</ExcludedFromBuild>
-      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Release|x64'">false</ExcludedFromBuild>
+      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">true</ExcludedFromBuild>
+      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">true</ExcludedFromBuild>
+      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Debug|ARM'">true</ExcludedFromBuild>
+      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Release|ARM'">true</ExcludedFromBuild>
+      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">true</ExcludedFromBuild>
+      <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Release|x64'">true</ExcludedFromBuild>
     </ClCompile>
+    <ClCompile Include="..\research\tests\ma_lpf_test_0.c" />
     <ClCompile Include="..\research\tests\ma_resampler_test_0.c">
       <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">true</ExcludedFromBuild>
       <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">true</ExcludedFromBuild>
@@ -409,6 +410,7 @@
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="..\miniaudio.h" />
+    <ClInclude Include="..\research\ma_lpf.h" />
     <ClInclude Include="..\research\ma_resampler.h" />
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />

tests/ma_test_0.vcxproj.filters

@@ -69,6 +69,9 @@
     <ClCompile Include="..\examples\fixed_size_callback.c">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\research\tests\ma_lpf_test_0.c">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="..\miniaudio.h">
@@ -77,5 +80,8 @@
     <ClInclude Include="..\research\ma_resampler.h">
       <Filter>Source Files</Filter>
     </ClInclude>
+    <ClInclude Include="..\research\ma_lpf.h">
+      <Filter>Source Files</Filter>
+    </ClInclude>
   </ItemGroup>
 </Project>