From 4a673e614bd91b7dafcd28701376a14cfd005063 Mon Sep 17 00:00:00 2001
From: goyuken <goyuken@4bbf4f03-6f44-549e-7e59-35d4b0962838>
Date: Sun, 9 Dec 2012 20:39:29 +0000
Subject: [PATCH] nes: apu: remove unbiasing from apu core.  blip_buf already
 handles a dc bias removal internally, and keeping all of the values to the
 mixer in their original forms is simpler code and probably reflects the
 underlying hardware more accurately.  should sound about the same as before.

---
 .../Consoles/Nintendo/NES/APU.cs              | 47 +++++++------------
 1 file changed, 18 insertions(+), 29 deletions(-)

diff --git a/BizHawk.Emulation/Consoles/Nintendo/NES/APU.cs b/BizHawk.Emulation/Consoles/Nintendo/NES/APU.cs
index 6177c40212..a1ad3ae636 100644
--- a/BizHawk.Emulation/Consoles/Nintendo/NES/APU.cs
+++ b/BizHawk.Emulation/Consoles/Nintendo/NES/APU.cs
@@ -263,17 +263,13 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 					if (duty_value) //high state of duty cycle
 					{
 						newsample = env_output;
-
-						if (swp_silence)
-							newsample = env_output >> 1; //(a little biasing hack here)
-
-						if (len_cnt == 0) //length counter is 0
-							newsample = env_output >> 1; //silenced (a little biasing hack here)
+						if (swp_silence || len_cnt == 0)
+							newsample = 0; // silenced
 					}
 					else
-						newsample = env_output >> 1; //duty cycle is 0, silenced.
+						newsample = 0; //duty cycle is 0, silenced.
 
-					newsample -= env_output >> 1; //unbias
+					//newsample -= env_output >> 1; //unbias
 					if (newsample != sample)
 					{
 						apu.recalculate = true;
@@ -428,11 +424,10 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 						noise_bit = (shift_register & 1) != 0;
 					}
 
-					//unbiasing is rolled in here
 					int newsample;
 					if (len_cnt == 0) newsample = 0;
-					else if (noise_bit) newsample = -env_output;
-					else newsample = env_output;
+					else if (noise_bit) newsample = env_output; // switched, was 0?
+					else newsample = 0;
 					if (newsample != sample)
 					{
 						apu.recalculate = true;
@@ -532,7 +527,7 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 							seq = (seq + 1) & 0x1F;
 							timer = timer_cnt_reload;
 						}
-						if(CFG_DECLICK)
+						if(CFG_DECLICK) // this looks ugly...
 							newsample = TRIANGLE_TABLE[(seq + 8) & 0x1F];
 						else
 							newsample = TRIANGLE_TABLE[seq];
@@ -542,7 +537,7 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 						//so we'll emulate it at the digital level
 						if (timer_cnt_reload == 1) newsample = 8;
 
-						newsample -= 8; //unbias
+						//newsample -= 8; //unbias
 						if (newsample != sample)
 						{
 							apu.recalculate = true;
@@ -615,7 +610,7 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 				int out_shift, out_bits_remaining, out_deltacounter;
 				bool out_silence;
 
-				public int sample { get { return out_deltacounter - 64; } }
+				public int sample { get { return out_deltacounter /* - 64*/; } }
 
 				public void SyncState(Serializer ser)
 				{
@@ -1022,11 +1017,6 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 				}
 			}
 
-			//public void DiscardSamples()
-			//{
-			//  metaspu.buffer.clear();
-			//}
-
 			int toggle = 0;
 			public void RunOne()
 			{
@@ -1074,11 +1064,6 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 				//we want the changes to affect it on the *next* cycle.
 			}
 
-			//int loopy = 0;
-			//public const int DECIMATIONFACTOR = 20;
-			//const int QUEUESIZE = 1789773 / DECIMATIONFACTOR; //1 second, should be enough
-			//public QuickQueue<short> squeue = new QuickQueue<short>(QUEUESIZE);
-
 			public struct Delta
 			{
 				public uint time;
@@ -1114,14 +1099,18 @@ namespace BizHawk.Emulation.Consoles.Nintendo
 					if (!EnableNoise) s_noise = 0;
 					if (!EnableDMC) s_dmc = 0;
 
-					const float NOISEADJUST = 0.5f;
+					//const float NOISEADJUST = 0.5f;
 
 					//linear approximation
-					float pulse_out = 0.00752f * (s_pulse0 + s_pulse1);
-					float tnd_out = 0.00851f * s_tri + 0.00494f * NOISEADJUST * s_noise + 0.00335f * s_dmc;
-					float output = pulse_out + tnd_out;
+					//float pulse_out = 0.00752f * (s_pulse0 + s_pulse1);
+					//float tnd_out = 0.00851f * s_tri + 0.00494f * /*NOISEADJUST * */ s_noise + 0.00335f * s_dmc;
+					//float output = pulse_out + tnd_out;
 					//this needs to leave enough headroom for straying DC bias due to the DMC unit getting stuck outputs. smb3 is bad about that. 
-					int mix = (int)(50000 * output);
+					//int mix = (int)(50000 * output);
+
+					int pulse_out = 376 * (s_pulse0 + s_pulse1);
+					int tnd_out = 426 * s_tri + 247 * s_noise + 167 * s_dmc;
+					int mix = pulse_out + tnd_out;
 
 					dlist.Add(new Delta(sampleclock, mix - oldmix));
 					oldmix = mix;