audio: change output rate to 47340Hz, add resampler with small margin to elimiate pops/clicks due to output rate fluctuation

output rate is picked such that 1024 samples at that rate equal exactly 710 samples at the SPU's output rate

src/SPU.cpp

@@ -684,19 +684,26 @@ void Mix(u32 samples)
 }
 
 
-void ReadOutput(s16* data, int samples)
+int ReadOutput(s16* data, int samples)
 {
+    if (OutputReadOffset == OutputWriteOffset)
+        return 0;
+
     for (int i = 0; i < samples; i++)
     {
         *data++ = OutputBuffer[OutputReadOffset];
         *data++ = OutputBuffer[OutputReadOffset + 1];
 
-        if (OutputReadOffset != OutputWriteOffset)
+        //if (OutputReadOffset != OutputWriteOffset)
         {
             OutputReadOffset += 2;
             OutputReadOffset &= ((2*OutputBufferSize)-1);
         }
+        if (OutputReadOffset == OutputWriteOffset)
+            return i+1;
     }
+
+    return samples;
 }
 
 

src/SPU.h

@@ -31,7 +31,7 @@ void SetBias(u16 bias);
 
 void Mix(u32 samples);
 
-void ReadOutput(s16* data, int samples);
+int ReadOutput(s16* data, int samples);
 
 u8 Read8(u32 addr);
 u16 Read16(u32 addr);

src/libui_sdl/main.cpp

@@ -96,7 +96,46 @@ void UpdateWindowTitle(void* data)
 
 void AudioCallback(void* data, Uint8* stream, int len)
 {
-    SPU::ReadOutput((s16*)stream, len>>2);
+    // resampling:
+    // buffer length is 1024 samples
+    // which is 710 samples at the original sample rate
+
+    //SPU::ReadOutput((s16*)stream, len>>2);
+    s16 buf_in[710*2];
+    s16* buf_out = (s16*)stream;
+
+    int num_in = SPU::ReadOutput(buf_in, 710);
+    int num_out = 1024;
+
+    int margin = 6;
+    if (num_in < 710-margin)
+    {
+        int last = num_in-1;
+        if (last < 0) last = 0;
+
+        for (int i = num_in; i < 710-margin; i++)
+            ((u32*)buf_in)[i] = ((u32*)buf_in)[last];
+
+        num_in = 710-margin;
+    }
+
+    float res_incr = num_in / (float)num_out;
+    float res_timer = 0;
+    int res_pos = 0;
+
+    for (int i = 0; i < 1024; i++)
+    {
+        // TODO: interp!!
+        buf_out[i*2  ] = buf_in[res_pos*2  ];
+        buf_out[i*2+1] = buf_in[res_pos*2+1];
+
+        res_timer += res_incr;
+        while (res_timer >= 1.0)
+        {
+            res_timer -= 1.0;
+            res_pos++;
+        }
+    }
 }
 
 int EmuThreadFunc(void* burp)
@@ -111,15 +150,9 @@ int EmuThreadFunc(void* burp)
     ScreenDrawInited = false;
     Touching = false;
 
-    // DS:
-    // 547.060546875 samples per frame
-    // 32823.6328125 samples per second
-    //
-    // 48000 samples per second:
-    // 800 samples per frame
     SDL_AudioSpec whatIwant, whatIget;
     memset(&whatIwant, 0, sizeof(SDL_AudioSpec));
-    whatIwant.freq = 32824; // 32823.6328125
+    whatIwant.freq = 47340;
     whatIwant.format = AUDIO_S16LSB;
     whatIwant.channels = 2;
     whatIwant.samples = 1024;