Audio: new dsp_coef.bin with windowed sinc filter coefficients

Source/Core/Core/DSP/DSPCore.cpp

@@ -42,7 +42,10 @@ static bool VerifyRoms()
 
 		// delroth's improvement on LM1234 replacement ROM (Zelda and AX only,
 		// IPL/Card/GBA still broken)
-		{ 0xd9907f71, 0xb019c2fb }
+		{ 0xd9907f71, 0xb019c2fb },
+
+		// above with improved resampling coefficients
+		{ 0xd9907f71, 0xdb6880c1 }
 	};
 
 	u32 hash_irom = HashAdler32((u8*)g_dsp.irom, DSP_IROM_BYTE_SIZE);
@@ -69,7 +72,7 @@ static bool VerifyRoms()
 		DSPHost::OSD_AddMessage("You are using an old free DSP ROM made by the Dolphin Team.", 6000);
 		DSPHost::OSD_AddMessage("Only games using the Zelda UCode will work correctly.", 6000);
 	}
-	else if (rom_idx == 2)
+	else if (rom_idx == 2 || rom_idx == 3)
 	{
 		DSPHost::OSD_AddMessage("You are using a free DSP ROM made by the Dolphin Team.", 8000);
 		DSPHost::OSD_AddMessage("All Wii games will work correctly, and most GC games should ", 8000);

docs/DSP/free_dsp_rom/dsp_rom_readme.txt

@@ -1,3 +1,16 @@
+Legal GC/WII DSP IROM replacement (v0.2.1)
+-------------------------------------------------------
+
+- coef: 4-tap polyphase FIR filters
+- irom: unchanged
+
+Coefficients are roughly equivalent to those in the official DROM.
+Improves resampling quality greatly over linear interpolation.
+See generate_coefs.py for details.
+
+stgn
+29/june/2015
+
 Legal GC/WII DSP IROM replacement (v0.2)
 -------------------------------------------------------
 

docs/DSP/free_dsp_rom/generate_coefs.py

@@ -0,0 +1,25 @@
+from numpy import *
+from struct import pack
+
+def pack_coefs(c):
+    cw = list(zip(c[   :128][::-1],
+                  c[128:256][::-1],
+                  c[256:384][::-1],
+                  c[384:   ][::-1]))
+    m = max(sum(x) for x in cw)
+    return b''.join(pack('>4h', *(int(round(n / m * 32767)) for n in x)) for x in cw)
+
+x = linspace(-2, 2, 512, endpoint=False)
+
+w1 = hamming(512)
+w2 = kaiser(512, pi * 9/4)
+
+coef_1 = [sinc(n * 0.5)  for n in x] * w1
+coef_2 = [sinc(n * 0.75) for n in x] * w2
+coef_3 = [sinc(n)        for n in x] * w1
+
+with open('dsp_coef.bin', 'wb') as f:
+    f.write(pack_coefs(coef_1))
+    f.write(pack_coefs(coef_2))
+    f.write(pack_coefs(coef_3))
+    f.write(b'\0' * 1024)