2taud.py: fix: stereo samples not converting correctly

it2taud.py

@@ -294,11 +294,11 @@ def _it214_decompress_block(payload: bytes, num_samples: int,
 
     return out
 
-def it214_decompress(blob: bytes, smp_offset: int, num_samples: int,
-                     is_16bit: bool, is_it215: bool) -> bytes:
-    """Decode IT2.14/IT2.15 compressed sample data. Returns raw PCM bytes (signed)."""
+def _it214_decompress_channel(blob: bytes, pos: int, num_samples: int,
+                              is_16bit: bool, is_it215: bool) -> tuple:
+    """Decode one channel of IT2.14/IT2.15 compressed data. Returns
+    (raw PCM bytes, next position after consumed blocks)."""
     block_size = 0x4000 if is_16bit else 0x8000
-    pos = smp_offset
     out_samples = []
 
     while len(out_samples) < num_samples:
@@ -318,9 +318,24 @@ def it214_decompress(blob: bytes, smp_offset: int, num_samples: int,
         result = bytearray(len(out_samples) * 2)
         for i, s in enumerate(out_samples):
             struct.pack_into('<h', result, i * 2, max(-32768, min(32767, s)))
-        return bytes(result)
+        return bytes(result), pos
     else:
-        return bytes(s & 0xFF for s in out_samples)
+        return bytes(s & 0xFF for s in out_samples), pos
+
+
+def it214_decompress(blob: bytes, smp_offset: int, num_samples: int,
+                     is_16bit: bool, is_it215: bool,
+                     is_stereo: bool = False) -> bytes:
+    """Decode IT2.14/IT2.15 compressed sample data. Returns raw PCM bytes
+    (signed). For stereo samples, returns the left channel block followed
+    by the right channel block (matching IT's on-disk SF_SS layout)."""
+    left, pos = _it214_decompress_channel(blob, smp_offset, num_samples,
+                                           is_16bit, is_it215)
+    if not is_stereo:
+        return left
+    right, _ = _it214_decompress_channel(blob, pos, num_samples,
+                                          is_16bit, is_it215)
+    return left + right
 
 
 # ── IT sample parser ──────────────────────────────────────────────────────────
@@ -384,7 +399,7 @@ def parse_samples(data: bytes, h: ITHeader, decompress: bool) -> list:
                     try:
                         is_it215 = bool(s.cvt & 0x04)
                         raw = it214_decompress(data, s.smp_point, s.length,
-                                               s.is_16bit, is_it215)
+                                               s.is_16bit, is_it215, s.is_stereo)
                         s.sample_data = normalise_sample(raw, True,
                                                           s.is_16bit, s.is_stereo, s.name)
                         s.length = len(s.sample_data)

mod2taud.py

@@ -592,7 +592,7 @@ def build_sample_inst_bin(samples: list) -> tuple:
 # PT hard-pans channels in LRRL order: 0=L 1=R 2=R 3=L (and tile for >4).
 def _default_channel_pan(ch_idx: int) -> int:
     side = (ch_idx % 4)
-    return 16 if side in (0, 3) else 47
+    return 8 if side in (0, 3) else 55
 
 
 def build_pattern(grid: list, ch_idx: int, default_pan: int,

taud_common.py

@@ -614,31 +614,44 @@ def build_project_data(*, project_name: str = '',
 
 def normalise_sample(raw: bytes, signed: bool, is_16bit: bool,
                      is_stereo: bool, name: str) -> bytes:
-    """Return unsigned 8-bit mono sample bytes, downmixing/depthing as needed."""
+    """Return unsigned 8-bit mono sample bytes, downmixing/depthing as needed.
+
+    Stereo samples are stored as a split (non-interleaved) layout — the full
+    left channel block followed by the full right channel block — matching the
+    on-disk format used by IT, S3M, and XM (Schism's SF_SS).
+    """
     out = []
-    stride = (2 if is_16bit else 1) * (2 if is_stereo else 1)
-    i = 0
-    while i + stride <= len(raw):
+    bps     = 2 if is_16bit else 1
+    chans   = 2 if is_stereo else 1
+    n_frames = len(raw) // (bps * chans)
+    chan_bytes = n_frames * bps
+
+    for i in range(n_frames):
         if is_16bit:
             if is_stereo:
-                l16 = struct.unpack_from('<h', raw, i)[0]
-                r16 = struct.unpack_from('<h', raw, i+2)[0]
+                l16 = struct.unpack_from('<h', raw, i*2)[0]
+                r16 = struct.unpack_from('<h', raw, chan_bytes + i*2)[0]
                 s = (l16 + r16) >> 1
             else:
-                s = struct.unpack_from('<h', raw, i)[0]
+                s = struct.unpack_from('<h', raw, i*2)[0]
             v = (s >> 8) + 128
         else:
             if is_stereo:
-                l8 = raw[i]; r8 = raw[i+1]
-                raw_s = (l8 + r8) // 2
+                l8 = raw[i]
+                r8 = raw[chan_bytes + i]
+                if signed:
+                    l_s = l8 - 256 if l8 >= 0x80 else l8
+                    r_s = r8 - 256 if r8 >= 0x80 else r8
+                    v = ((l_s + r_s) >> 1) + 128
+                else:
+                    v = (l8 + r8) >> 1
             else:
                 raw_s = raw[i]
-            if signed:
-                v = (raw_s ^ 0x80) & 0xFF
-            else:
-                v = raw_s
+                if signed:
+                    v = (raw_s ^ 0x80) & 0xFF
+                else:
+                    v = raw_s
         out.append(v & 0xFF)
-        i += stride
     if is_16bit or is_stereo:
         vprint(f"  info: '{name}' converted to unsigned 8-bit mono ({len(out)} samples)")
     return bytes(out)