guidoschmidt · May 23, 2025 19:27 · Dec 10, 2016 · Dec 10, 2016 · Dec 10, 2016 · Dec 10, 2016
diff --git a/core-audio-sine-wave.c b/core-audio-sine-wave.c
@@ -16,9 +16,9 @@ OSStatus RenderSineWave(
 {
     static float theta;
 
-    float *left = (float *)ioData->mBuffers[0].mData;
+    SInt16 *left = (SInt16 *)ioData->mBuffers[0].mData;
     for (UInt32 frame = 0; frame < inNumberFrames; ++frame) {
-        left[frame] = sin(theta);
+        left[frame] = (SInt16)(sin(theta) * 32767.0f);
         theta += M_TAU * TONE_FREQUENCY / SAMPLE_RATE;
         if (theta > M_TAU) {
             theta -= M_TAU;
@@ -54,13 +54,16 @@ int main() {
 
     AudioStreamBasicDescription asbd = {
         .mFormatID = kAudioFormatLinearPCM,
-        .mFormatFlags = kAudioFormatFlagsNativeFloatPacked | kAudioFormatFlagIsNonInterleaved,
+        .mFormatFlags = 0
+            | kAudioFormatFlagIsSignedInteger
+            | kAudioFormatFlagIsPacked
+            | kAudioFormatFlagIsNonInterleaved,
         .mSampleRate = 48000,
-        .mBitsPerChannel = 32,
+        .mBitsPerChannel = 16,
         .mChannelsPerFrame = 2,
         .mFramesPerPacket = 1,
-        .mBytesPerFrame = 4,
-        .mBytesPerPacket = 4,
+        .mBytesPerFrame = 2,
+        .mBytesPerPacket = 2,
     };
 
     err = AudioUnitSetProperty(toneUnit, kAudioUnitProperty_StreamFormat,
@@ -73,9 +76,9 @@ int main() {
     err = AudioOutputUnitStart(toneUnit);
     if (err) printf("Error starting unit: %d\n", err);
 
-    usleep(2000000);
+    usleep(500000);
 
     AudioOutputUnitStop(toneUnit);
     AudioUnitUninitialize(toneUnit);
     AudioComponentInstanceDispose(toneUnit);
-}
+}
diff --git a/core-audio-sine-wave.c b/core-audio-sine-wave.c
@@ -54,9 +54,7 @@ int main() {
 
     AudioStreamBasicDescription asbd = {
         .mFormatID = kAudioFormatLinearPCM,
-        .mFormatFlags = 0
-            | kAudioFormatFlagsNativeFloatPacked
-            | kAudioFormatFlagIsNonInterleaved,
+        .mFormatFlags = kAudioFormatFlagsNativeFloatPacked | kAudioFormatFlagIsNonInterleaved,
         .mSampleRate = 48000,
         .mBitsPerChannel = 32,
         .mChannelsPerFrame = 2,

diff --git a/core-audio-sine-wave.c b/core-audio-sine-wave.c
@@ -47,8 +47,7 @@ int main() {
     err = AudioComponentInstanceNew(output, &toneUnit);
     if (err) fprintf(stderr, "Error creating unit: %d\n", err);
 
-    AURenderCallbackStruct input = {0};
-    input.inputProc = RenderSineWave;
+    AURenderCallbackStruct input = { .inputProc = RenderSineWave };
     err = AudioUnitSetProperty(toneUnit, kAudioUnitProperty_SetRenderCallback,
             kAudioUnitScope_Input, 0, &input, sizeof(input));
     if (err) printf("Error setting callback: %d\n", err);

diff --git a/core-audio-sine-wave.c b/core-audio-sine-wave.c
@@ -2,9 +2,9 @@
 //   clang core-audio-sine-wave.c -framework AudioUnit && ./a.out
 #include <AudioUnit/AudioUnit.h>
 
-#define SAMPLING_RATE 48000
+#define SAMPLE_RATE 48000
 #define TONE_FREQUENCY 440
-#define M_TAU 2 * M_PI
+#define M_TAU 2.0 * M_PI
 
 OSStatus RenderSineWave(
         void *inRefCon,
@@ -15,26 +15,30 @@ OSStatus RenderSineWave(
         AudioBufferList *ioData)
 {
     static float theta;
-    float *channel = (float *)ioData->mBuffers[0].mData;
+
+    float *left = (float *)ioData->mBuffers[0].mData;
     for (UInt32 frame = 0; frame < inNumberFrames; ++frame) {
-        channel[frame] = sin(theta);
-        theta += M_TAU * TONE_FREQUENCY / SAMPLING_RATE;
+        left[frame] = sin(theta);
+        theta += M_TAU * TONE_FREQUENCY / SAMPLE_RATE;
         if (theta > M_TAU) {
             theta -= M_TAU;
         }
     }
+
+    // Copy left channel to right channel
+    memcpy(ioData->mBuffers[1].mData, left, ioData->mBuffers[1].mDataByteSize);
+
     return noErr;
 }
 
 int main() {
     OSErr err;
 
-    AudioComponentDescription acd;
-    acd.componentType = kAudioUnitType_Output;
-    acd.componentSubType = kAudioUnitSubType_DefaultOutput;
-    acd.componentManufacturer = kAudioUnitManufacturer_Apple;
-    acd.componentFlags = 0;
-    acd.componentFlagsMask = 0;
+    AudioComponentDescription acd = {
+        .componentType = kAudioUnitType_Output,
+        .componentSubType = kAudioUnitSubType_DefaultOutput,
+        .componentManufacturer = kAudioUnitManufacturer_Apple,
+    };
 
     AudioComponent output = AudioComponentFindNext(NULL, &acd);
     if (!output) printf("Can't find default output\n");
@@ -43,22 +47,24 @@ int main() {
     err = AudioComponentInstanceNew(output, &toneUnit);
     if (err) fprintf(stderr, "Error creating unit: %d\n", err);
 
-    AURenderCallbackStruct input;
+    AURenderCallbackStruct input = {0};
     input.inputProc = RenderSineWave;
-    input.inputProcRefCon = NULL;
     err = AudioUnitSetProperty(toneUnit, kAudioUnitProperty_SetRenderCallback,
             kAudioUnitScope_Input, 0, &input, sizeof(input));
     if (err) printf("Error setting callback: %d\n", err);
 
-    AudioStreamBasicDescription asbd;
-    asbd.mFormatID = kAudioFormatLinearPCM;
-    asbd.mFormatFlags = kAudioFormatFlagsNativeFloatPacked;
-    asbd.mSampleRate = SAMPLING_RATE;
-    asbd.mBitsPerChannel = 32;
-    asbd.mChannelsPerFrame = 1;
-    asbd.mFramesPerPacket = 1;
-    asbd.mBytesPerFrame = asbd.mBitsPerChannel / 8 * asbd.mChannelsPerFrame;
-    asbd.mBytesPerPacket = asbd.mBytesPerFrame * asbd.mFramesPerPacket;
+    AudioStreamBasicDescription asbd = {
+        .mFormatID = kAudioFormatLinearPCM,
+        .mFormatFlags = 0
+            | kAudioFormatFlagsNativeFloatPacked
+            | kAudioFormatFlagIsNonInterleaved,
+        .mSampleRate = 48000,
+        .mBitsPerChannel = 32,
+        .mChannelsPerFrame = 2,
+        .mFramesPerPacket = 1,
+        .mBytesPerFrame = 4,
+        .mBytesPerPacket = 4,
+    };
 
     err = AudioUnitSetProperty(toneUnit, kAudioUnitProperty_StreamFormat,
             kAudioUnitScope_Input, 0, &asbd, sizeof(asbd));

diff --git a/core-audio-sine-wave.c b/core-audio-sine-wave.c
@@ -57,8 +57,8 @@ int main() {
     asbd.mBitsPerChannel = 32;
     asbd.mChannelsPerFrame = 1;
     asbd.mFramesPerPacket = 1;
-    asbd.mBytesPerFrame = 4;
-    asbd.mBytesPerPacket = 4;
+    asbd.mBytesPerFrame = asbd.mBitsPerChannel / 8 * asbd.mChannelsPerFrame;
+    asbd.mBytesPerPacket = asbd.mBytesPerFrame * asbd.mFramesPerPacket;
 
     err = AudioUnitSetProperty(toneUnit, kAudioUnitProperty_StreamFormat,
             kAudioUnitScope_Input, 0, &asbd, sizeof(asbd));

diff --git a/core-audio-sine-wave.c b/core-audio-sine-wave.c
@@ -0,0 +1,78 @@
+// To run:
+//   clang core-audio-sine-wave.c -framework AudioUnit && ./a.out
+#include <AudioUnit/AudioUnit.h>
+
+#define SAMPLING_RATE 48000
+#define TONE_FREQUENCY 440
+#define M_TAU 2 * M_PI
+
+OSStatus RenderSineWave(
+        void *inRefCon,
+        AudioUnitRenderActionFlags *ioActionFlags,
+        const AudioTimeStamp *inTimeStamp,
+        UInt32 inBusNumber,
+        UInt32 inNumberFrames,
+        AudioBufferList *ioData)
+{
+    static float theta;
+    float *channel = (float *)ioData->mBuffers[0].mData;
+    for (UInt32 frame = 0; frame < inNumberFrames; ++frame) {
+        channel[frame] = sin(theta);
+        theta += M_TAU * TONE_FREQUENCY / SAMPLING_RATE;
+        if (theta > M_TAU) {
+            theta -= M_TAU;
+        }
+    }
+    return noErr;
+}
+
+int main() {
+    OSErr err;
+
+    AudioComponentDescription acd;
+    acd.componentType = kAudioUnitType_Output;
+    acd.componentSubType = kAudioUnitSubType_DefaultOutput;
+    acd.componentManufacturer = kAudioUnitManufacturer_Apple;
+    acd.componentFlags = 0;
+    acd.componentFlagsMask = 0;
+
+    AudioComponent output = AudioComponentFindNext(NULL, &acd);
+    if (!output) printf("Can't find default output\n");
+
+    AudioUnit toneUnit;
+    err = AudioComponentInstanceNew(output, &toneUnit);
+    if (err) fprintf(stderr, "Error creating unit: %d\n", err);
+
+    AURenderCallbackStruct input;
+    input.inputProc = RenderSineWave;
+    input.inputProcRefCon = NULL;
+    err = AudioUnitSetProperty(toneUnit, kAudioUnitProperty_SetRenderCallback,
+            kAudioUnitScope_Input, 0, &input, sizeof(input));
+    if (err) printf("Error setting callback: %d\n", err);
+
+    AudioStreamBasicDescription asbd;
+    asbd.mFormatID = kAudioFormatLinearPCM;
+    asbd.mFormatFlags = kAudioFormatFlagsNativeFloatPacked;
+    asbd.mSampleRate = SAMPLING_RATE;
+    asbd.mBitsPerChannel = 32;
+    asbd.mChannelsPerFrame = 1;
+    asbd.mFramesPerPacket = 1;
+    asbd.mBytesPerFrame = 4;
+    asbd.mBytesPerPacket = 4;
+
+    err = AudioUnitSetProperty(toneUnit, kAudioUnitProperty_StreamFormat,
+            kAudioUnitScope_Input, 0, &asbd, sizeof(asbd));
+    if (err) printf("Error setting stream format: %d\n", err);
+
+    err = AudioUnitInitialize(toneUnit);
+    if (err) printf("Error initializing unit: %d\n", err);
+
+    err = AudioOutputUnitStart(toneUnit);
+    if (err) printf("Error starting unit: %d\n", err);
+
+    usleep(2000000);
+
+    AudioOutputUnitStop(toneUnit);
+    AudioUnitUninitialize(toneUnit);
+    AudioComponentInstanceDispose(toneUnit);
+}
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