A filter after an FM voice: the FS1R's, SY77's, Montage FM-X's and Virus's filter on the FM output #156

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opened 2026-10-06 16:24:13 +00:00 by bcox · 0 comments

bcox commented

2026-10-06 16:24:13 +00:00

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bcox asked on 2026-10-06 for a ticket for each gap docs/feature-survey.md names without one, whether or not it is ever done. Engine claims are from reading the tree at 6a3fede9 on main. Instrument claims are from that document's research, read from the manuals by research agents and not re-checked; the sources are listed there. Nothing here is built, measured or listened to.

Summary

The FM pair has a formant bank and a shaper insert and no filter; a filter after it is a VA layer reading its tap. The FS1R has one filter per voice of six types with an envelope, the SY77 two 12 dB filters per element into oscillation, the Montage FM-X a part filter of 22 types with scaling, and the Virus TI2 runs its FM through its two filters. #14 (closed) asked "Put a filter at the end of the layer chain? Or an EQ?" and the formant bank is what came of it.

What the tree has

kCarrierFormant1Hz through the third band's level, and the modulators' bands; the shaper insert; a VA layer on the tap as the route.

The work, as a sketch

One filter slot on the pair, the SVF or the ladder, with cutoff, resonance and keytrack lanes and an envelope, sharing dsp/va_filter.h; or nothing, with the tap route recorded as the answer.

Open

Whether the route's cost, one layer slot per FM layer, is paid often enough to matter.

bcox asked on 2026-10-06 for a ticket for each gap `docs/feature-survey.md` names without one, whether or not it is ever done. Engine claims are from reading the tree at `6a3fede9` on `main`. Instrument claims are from that document's research, read from the manuals by research agents and not re-checked; the sources are listed there. **Nothing here is built, measured or listened to.** ## Summary The FM pair has a formant bank and a shaper insert and no filter; a filter after it is a VA layer reading its tap. The FS1R has one filter per voice of six types with an envelope, the SY77 two 12 dB filters per element into oscillation, the Montage FM-X a part filter of 22 types with scaling, and the Virus TI2 runs its FM through its two filters. #14 (closed) asked "Put a filter at the end of the layer chain? Or an EQ?" and the formant bank is what came of it. ## What the tree has - `kCarrierFormant1Hz` through the third band's level, and the modulators' bands; the shaper insert; a VA layer on the tap as the route. ## The work, as a sketch - One filter slot on the pair, the SVF or the ladder, with cutoff, resonance and keytrack lanes and an envelope, sharing `dsp/va_filter.h`; or nothing, with the tap route recorded as the answer. ## Open Whether the route's cost, one layer slot per FM layer, is paid often enough to matter.