Spectrum
Spectrum: main parameter page.
A filter pedal that replaces stock FILTER: a Moog ladder, an Oberheim SEM state-variable filter, an isolator and a formant bank, with an envelope and an LFO on the cutoff. The defaults are an exact passthrough, so a part that chose FILTER sounds the same until you turn it.
Access
Press FX1 on a track; SPECTRUM is in the chooser in place of FILTER. In Octabam Inserts it is also on FX2; in Octabam Bus it is FX1 only.
Operation
- MODE on page 2 picks the filter:
- LADR — a 24 dB/oct Moog transistor ladder. RES 127 is the edge of self-oscillation; the passband level drops as RES rises, so the output carries a makeup that keeps it close.
- SEM — a driven Oberheim state-variable filter. SHPE (page 2) sweeps it low-pass (0) → band-pass (64) → high-pass (127) with an equal-power crossfade.
- ISO — an isolator. FREQ is the low band's cutoff, RES is COLR.
- VOWL — a three-formant bank that morphs A → E → I → O → U as FREQ turns; RES (SHRP) narrows the bands.
- ENV is a peak follower onto the cutoff: instant attack, release on LSP. LDP is an LFO onto the cutoff; LSP sets its speed (~0.08–9 Hz).
- WDTH is mid/side width on the output; the centre (64) is untouched.
Parameters
| Page | Knob | Range | Default | What it does |
|---|---|---|---|---|
| 1 | FREQ | 0–127 | 127 | the cutoff, exponential, 60 Hz → 15 kHz; LOW in ISO; the vowel morph in VOWL |
| 1 | RES | 0–127 | 0 | resonance; COLR in ISO; SHRP (band narrowing) in VOWL |
| 1 | ENV | bipolar | 64 | envelope onto the cutoff: instant attack, LSP is the release |
| 1 | LDP | 0–127 | 0 | LFO onto the cutoff |
| 1 | LSP | 0–127 | 64 | LFO speed ~0.08–9 Hz; ENV's release |
| 1 | WDTH | bipolar | 64 | mid/side width on the output |
| 2 | MODE | LADR / SEM / ISO / VOWL | — | Selects the filter model. |
| 2 | SHPE | 0–127 | 0 | SEM only (blank in other modes): LP → BP → HP |
Old Projects
MODE's saved values moved on 27 Sep 2026 (BP 2 → SEM 1, ISO 3 → 2, VOWL 4 → 3); SHPE keeps its stored value, so a part saved on BP comes back as SEM at whatever SHPE it held. Once per project, before play:
python3 tools/hw/ot_project.py remap-slot <project> SPECTRUM MODE 2:1,3:2,4:3
Screen Reference
Spectrum: effect selection and setup parameters.
Status: on hardware: Sam's MKII.
Module facts (developers)
FX1 station: a filter pedal -- the Moog ladder, SEM (LP -> BP -> HP by SHPE), Airwindows Capacitor2, formants; ENV and LFO onto the cutoff; width.
| Detail | Value |
|---|---|
| Author | sambanks |
| Category | Effects: on a track |
| Kind | hybrid |
| Test status | on hardware: Sam's MKII |
| FX2 ID | 0x04 |
| Parameters | FREQ@0, RES@1, ENV@2, LDP@3, LSP@4, WDTH@5, MODE@6, SHPE@7 |
| Included in | octabam-bus, octabam-inserts |
On GitHub: https://github.com/sambanks/octabam/blob/main/modules/spectrum/README.md