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https://github.com/RetroPortingToolKit/psxrecomp
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Matthew Stanley
462e2bf5fd
An ADPCM block whose flags carry END (bit 0) but not REPEAT (bit 1)
must (a) jump the decode pointer to the latched repeat address and
(b) force the ADSR envelope to ZERO on entering Release — Beetle
spu.cpp:333 (CurAddr = LoopAddr, unconditional) and :341-352 ("Force
enveloping to 0 if not looping"). Our voice_next_sample did neither:
it entered Release with the envelope intact and kept decoding FORWARD
past the terminator, assuming the release ramp would mask whatever
followed in SPU RAM.
X4's SFX bank breaks that assumption three ways: its one-shot samples
terminate on an END-only block; the next block in RAM is non-silent
filler (0x77 nibbles at shift 0 = constant +28672) carrying a
self-referential LOOPSTART flag, so the walker parks there forever;
and the bank's ADSR release shift is ~infinite, so the envelope never
decays. Every finished SFX voice became a full-scale DC source. In the
X4 attract ice-stage demo (user report), a handful of ice-block-break
SFX stacked ~15 such voices and pinned the whole mix at +32767 for
~35 s — heard as static / the music "cutting out". Measured: 38-41%
of samples hard-clipped in the spu_out AND host taps during the demo.
With the fix (jump + env=0; the env-0 Release path then deactivates
the voice, matching Beetle's silent-voice behavior): 0.00% clipped
samples over the same demo window, peak 32291, zero railed polls in
150 across the full attract cycle; the ice-crack SFX bodies still
play normally.
Found via the new rail-triggered spu_voices capture + the spu_ram
peek: 15 voices sharing start=0x16AD0 all parked at cur_addr=0x17930
looping 0x17920 (flags 0x07) at env 0x7FBF in phase RELEASE, and the
block bytes 00 07 77 77 .. decoding to +28672 DC.
Debug surface added (always-on doctrine):
- spu_voices now reports live env level + ADSR phase per voice.
- new spu_ram command: {"addr","len"} -> hex peek of SPU sample RAM.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>