Musica.Studio has released FSVR, a free software reconstruction of the Yamaha FS1R, the formant-shaping FM synthesizer Yamaha built in 1998. Version 0.4.0 went out on 21 September and runs as a standalone application and as VST3 and CLAP plugins on Windows, macOS and Linux.
The project is not an emulation of the original hardware. Rather than model the processor on the FS1R's board, developers James Hansen and Zhiyuan Wan took the decompiled FS1R firmware and rewrote its logic in C++, porting the note-on path, the tick pipeline and the parameter conversion tables from decompiled source. Musica.Studio describes it as “a rewrite, not an emulation of the board”. The work builds on Wan's earlier reverse engineering of the synth, which produced the ROM loader image and Ghidra databases the rebuild draws on, and the repository credits AI coding agents, Claude models among them, with assisting the firmware analysis and engine work.
What is in the download
The release bundles the FS1R's factory content — 1,408 voices, 384 performances and 90 formant sequences — so no EPROM image is needed. All 88 FM algorithms are implemented, with voiced and unvoiced operators, and formant sequence playback covers loop modes, start delay and MIDI clock sync. The front panel interface is derived from the screen tables in the firmware. There is no installer and no dependencies; Musica.Studio says uninstalling means deleting the files.
Accuracy against the hardware
FSVR is an early alpha and the developers say so. The repository states that the project is “still in development, still not fully accurate to hardware”, and lists the effects algorithms, some formant behaviour and filter envelope accuracy as known gaps. Measured against Wan's recordings of an FS1R playing its own demo songs, median envelope correlation is 0.978, and 17 of 29 captured files agree with the hardware to within half a decibel of level.
The v0.4.0 notes describe recalibration drawn from hardware measurements, including key rate scaling in the amplitude envelope, a formant window reworked as a time-based parameter and a detune table taken from the EPROM. On the Full Tines demo, Musica.Studio reports envelope correlation moving from 0.838 to 0.976. The plugin was also renamed for this release — earlier builds went out as FS1R.emu — so sessions saved with those versions need to be reconfigured. FSVR is licensed under GPLv3.
Via Musica.Studio. Downloads and source are on GitHub.