Cracked sound generated when modulation enabled at high frequency

[mckuhei]

2024-10-20.08-31-27.mp4

Test midi:
Crackedsound.zip

[jcmoyer]

Possibly caused by out of range values in pcm multi, but not sure what the fix would be.

Nuked-SC55/src/pcm.cpp

Lines 288 to 301 in 205ff94

	inline int32_t multi(int32_t val1, int8_t val2)
	{
	if (val1 & 0x80000)
	val1 |= ~0xfffff;
	else
	val1 &= 0x7ffff;
	val1 *= val2;
	if (val1 & 0x8000000)
	val1 |= ~0x1ffffff;
	else
	val1 &= 0x1ffffff;
	return val1;
	}

EDIT: Can someone test this midi on real hardware and report what happens?

[Axis4s]

Gui got more development?

[mckuhei]

No, this is my own branch.

[linoshkmalayil]

Possibly caused by out of range values in pcm multi, but not sure what the fix would be.

Nuked-SC55/src/pcm.cpp

Lines 288 to 301 in 205ff94

	inline int32_t multi(int32_t val1, int8_t val2)
	{
	if (val1 & 0x80000)
	val1 |= ~0xfffff;
	else
	val1 &= 0x7ffff;
	val1 *= val2;
	if (val1 & 0x8000000)
	val1 |= ~0x1ffffff;
	else
	val1 &= 0x1ffffff;
	return val1;
	}

EDIT: Can someone test this midi on real hardware and report what happens?

I tested this out on my SC-88Pro and SC-55mkII, both do not produce this cracked sound.
Tested it on the Nuked SC-55 running SC-55mkII roms, produces this cracked sound
So it seems this is a Nuked SC-55 issue.

[jcmoyer]

Seems to fix the problem for mk2:

diff --git a/src/pcm.cpp b/src/pcm.cpp
index 0cd1c29..b048fb0 100644
--- a/src/pcm.cpp
+++ b/src/pcm.cpp
@@ -1410,7 +1410,9 @@ void PCM_Update(uint64_t cycles)
                 int v1 = v2 + (mult2 >> 13) + ((mult2 >> 12) & 1); // 10
                 int subvar = v1 + (mult3 >> 6) + ((mult3 >> 5) & 1); // 11

-                ram1[3] = v1;
+#define Clamp(v, x0, x1) (v < x0 ? x0 : v > x1 ? x1 : v)
+
+                ram1[3] = Clamp(v1, -0x80000, 0x7ffff);

                 int tests = test;
                 tests <<= 12;
@@ -1423,7 +1425,7 @@ void PCM_Update(uint64_t cycles)
                 int v4 = reg1 + (mult4 >> 6) + ((mult4 >> 5) & 1); // 14
                 int v5 = v4 + (mult5 >> 13) + ((mult5 >> 12) & 1); // 15

-                ram1[1] = v5;
+                ram1[1] = Clamp(v5, -0x80000, 0x7ffff);
             }

Here's an audio comparison before/after: CrackleFixRenders.zip

The crackling version seems to have a lot more noise overall but I think it's just reverb from the crackling. If you invert one of the tracks and play them simultaneously the only thing left is the crackling.

[Grieferus]

Kind of offtopic question: where did you get the version with GUI?

[MusicallyInspired]

He said it was his own branch.

[mckuhei]

Gui is in my fork and can be downloaded here: https://github.com/mckuhei/Nuked-SC55/releases/tag/gui-v1.0

[Grieferus]

Seems to fix the problem for mk2:

diff --git a/src/pcm.cpp b/src/pcm.cpp
index 0cd1c29..b048fb0 100644
--- a/src/pcm.cpp
+++ b/src/pcm.cpp
@@ -1410,7 +1410,9 @@ void PCM_Update(uint64_t cycles)
                 int v1 = v2 + (mult2 >> 13) + ((mult2 >> 12) & 1); // 10
                 int subvar = v1 + (mult3 >> 6) + ((mult3 >> 5) & 1); // 11

-                ram1[3] = v1;
+#define Clamp(v, x0, x1) (v < x0 ? x0 : v > x1 ? x1 : v)
+
+                ram1[3] = Clamp(v1, -0x80000, 0x7ffff);

                 int tests = test;
                 tests <<= 12;
@@ -1423,7 +1425,7 @@ void PCM_Update(uint64_t cycles)
                 int v4 = reg1 + (mult4 >> 6) + ((mult4 >> 5) & 1); // 14
                 int v5 = v4 + (mult5 >> 13) + ((mult5 >> 12) & 1); // 15

-                ram1[1] = v5;
+                ram1[1] = Clamp(v5, -0x80000, 0x7ffff);
             }

Here's an audio comparison before/after: CrackleFixRenders.zip

The crackling version seems to have a lot more noise overall but I think it's just reverb from the crackling. If you invert one of the tracks and play them simultaneously the only thing left is the crackling.

I'd propose merging this with master branch, no matter how specific this bug might be.