diff --git a/extern/ESFMu/esfm.c b/extern/ESFMu/esfm.c
index 64d142e0d..e033b4d45 100644
--- a/extern/ESFMu/esfm.c
+++ b/extern/ESFMu/esfm.c
@@ -1751,7 +1751,7 @@ ESFM_process_feedback(esfm_chip *chip)
 		uint32 basefreq, phase_offset;
 		uint3 block;
 		uint10 f_num;
-		int32_t in1 = 0, in2 = 0, wave_out;
+		int32_t wave_out, wave_last;
 		int32_t phase_feedback;
 		uint19 regressed_phase;
 		int iter_counter;
@@ -1792,55 +1792,68 @@ ESFM_process_feedback(esfm_chip *chip)
 				"movl   %%r11d, %k[out]             \n\t"
 				"movw   $29, %%dx                   \n"
 				"1:                                 \n\t"
-				"movl   %k[p_acc], %%eax            \n\t"
-				"shrl   $9, %%eax                   \n\t"
+				// phase_feedback = (wave_out + wave_last) >> 2;
 				"movl   %k[out], %k[p_fb]           \n\t"
 				"addl   %%r11d, %k[p_fb]            \n\t"
 				"sarl   $2, %k[p_fb]                \n\t"
+				// wave_last = wave_out
+				"movl   %k[out], %%r11d             \n\t"
+				// phase = phase_feedback >> mod_in_shift;
 				"movl   %k[p_fb], %%ebx             \n\t"
 				"movb   %b[mod_in], %%cl            \n\t"
 				"sarl   %%cl, %%ebx                 \n\t"
+				// phase += phase_acc >> 9;
+				"movl   %k[p_acc], %%eax            \n\t"
+				"shrl   $9, %%eax                   \n\t"
 				"addl   %%ebx, %%eax                \n\t"
+				// lookup = logsinrom[(waveform << 10) | (phase & 0x3ff)];
 				"andq   $0x3ff, %%rax               \n\t"
-				"movl   %k[out], %%r11d             \n\t"
-				"movl   $0x1fff, %%ecx              \n\t"
 				"movzwl (%%r8, %%rax, 2), %%ebx     \n\t"
 				"movl   %%ebx, %%eax                \n\t"
+				// level = (lookup & 0x1fff) + (envelope << 3);
+				"movl   $0x1fff, %%ecx              \n\t"
 				"andl   %%ecx, %%eax                \n\t"
 				"addl   %%r10d, %%eax               \n\t"
+				// if (level > 0x1fff) level = 0x1fff;
 				"cmpl   %%ecx, %%eax                \n\t"
 				"cmoval %%ecx, %%eax                \n\t"
+				// wave_out = exprom[level & 0xff] >> (level >> 8);
 				"movb   %%ah, %%cl                  \n\t"
 				"movzbl %%al, %%eax                 \n\t"
 				"movzwl (%%r9, %%rax, 2), %k[out]   \n\t"
-				"shrl   %%cl, %k[out]               \n\t" 
+				"shrl   %%cl, %k[out]               \n\t"
+				// if (lookup & 0x8000) wave_out = -wave_out;
+				// in other words, lookup is negative
 				"movl   %k[out], %%ecx              \n\t"
 				"negl   %%ecx                       \n\t"
 				"testw  %%bx, %%bx                  \n\t"
 				"cmovsl %%ecx, %k[out]              \n\t"
+				// phase_acc += phase_offset
 				"addl   %k[p_off], %k[p_acc]        \n\t"
+				// loop
 				"decw   %%dx                        \n\t"
 				"jne    1b                          \n\t"
-				: [p_fb]   "+r" (phase_feedback),
-				[p_acc]  "+r" (phase_acc),
-				[out]    "+r" (wave_out)
-				: [p_off]  "g"  ((uint32_t)phase_offset),
-				[mod_in] "g"  ((uint8_t)mod_in_shift),
-				[wave]   "g"  ((uint8_t)waveform),
-				[eg_out] "g"  ((uint32_t)eg_output),
-				[sinrom] "m"  (logsinrom),
-				[exprom] "m"  (exprom)
+				: [p_fb]   "=&r" (phase_feedback),
+				  [p_acc]  "+r"  (phase_acc),
+				  [out]    "+r"  (wave_out)
+				: [p_off]  "g"   ((uint32_t)phase_offset),
+				  [mod_in] "g"   ((uint8_t)mod_in_shift),
+				  [wave]   "g"   ((uint8_t)waveform),
+				  [eg_out] "g"   ((uint32_t)eg_output),
+				  [sinrom] "m"   (logsinrom),
+				  [exprom] "m"   (exprom)
 				: "cc", "ax", "bx", "cx", "dx", "r8", "r9", "r10", "r11"
 			);
 #else
+			wave_out = 0;
+			wave_last = 0;
 			for (iter_counter = 28; iter_counter >= 0; iter_counter--)
 			{
-				phase = phase_acc >> 9;
-				phase_feedback = (in1 + in2) >> 2;
-				phase += phase_feedback >> mod_in_shift;
+				phase_feedback = (wave_out + wave_last) >> 2;
+				wave_last = wave_out;
+				phase = phase_feedback >> mod_in_shift;
+				phase += phase_acc >> 9;
 				wave_out = ESFM_envelope_wavegen(waveform, phase, eg_output);
-				in2 = in1;
-				in1 = wave_out;
 				phase_acc += phase_offset;
 			}
 #endif