Port of krom (Peter Lemon)'s PitchMod demo. The S-DSP's PMON feature multiplies a voice's pitch by the output of the previous voice, every sample, in hardware. Voice 1 holds a looping cello note at C5; voice 0 plays a 9-byte square-wave BRR block at pitch $0003 — far below audibility, it is a slow LFO whose tiny amplitude (GAIN = 2) sets the vibrato depth. The cello enters dry; one second in, the LFO keys on and the note starts to sing. Each note rings out like a bow stroke (instant attack, ~7 s fade — the ADSR the sample was shipped with) and is re-bowed every 7 s. A maximum-length FIR echo (EDL 15, feedback 100) does the concert hall.

ROM mode: LoROM (project default).

Measured against the original (luna --audio-out, same window): pitch 174.4 Hz vs 174.3 Hz, vibrato depth ±0.82 % on both, LFO rate ~5 Hz on both.

Why the envelope differs from the original (a true story)

krom's demo sets a flat GAIN 127 — which would sustain the note forever — yet his demo audibly decays like a bow stroke. The reason: his SPC700 program has no final idle loop. After the last KON, execution falls off the end of the code, through the sample directory, and starts executing the cello's BRR bytes as opcodes (verified with luna's spc-dump: his SPC700 PC ends up at $0548, inside the sample data). The decay in the original is that runaway code eventually scribbling on the DSP registers — an accident, not a design.

This port keeps the bow-stroke sound but produces it on purpose: the cello's filename in krom's repo encodes its intended envelope (ADSR $FF/$E8 — instant attack, sustain level 7/8, gentle rate-8 fade), so we program that ADSR, park the CPU in a clean idle loop, and re-key the voice every 7 s for the next stroke.

SNES Concepts

Pitch modulation (PMON): voice N−1's output scales voice N's pitch
A silent voice as a hardware LFO — GAIN is the vibrato depth, PITCH is the vibrato rate
ADSR envelope as articulation — instant attack + slow sustain-rate fade = a bow stroke; re-KON = the next stroke
Sample directory layout ([start][loop] pairs) with a hand-written single-block BRR wave next to an .incbin sample
Raw APU programming via the apu module (IPL upload from C)

Sample provenance

res/cello.brr is the cello sample shipped with krom's PitchMod demo (loop point 4167, played at his exact C5 pitch $08BB = $8BB0 >> 4). See ATTRIBUTION.md at the repo root for the provenance caveat.

How to Build

make

Modules Used

console, apu