DigiFilter

DigiFilter 1.3 for the Digitakt mk1 (OS 1.54) and Digitone mk1/Keys (OS 1.44).

What is in the package

• digifilter-1.3.elemod - Digitakt mk1, DigiFilter: BP, BP2, COMB, TRASH, OB4, OB2 (TYPE 8..13).
• digifilter-dn-1.3.elemod - Digitone mk1/Keys, DigiFilter: the same BP, BP2, COMB, TRASH, OB4, OB2 modes (TYPE 4..9), with page-2 HARM/DAMP and TYPE persistence.

Both machines are built at 1.3 from the same shared DSP source. One elemod per machine, latest OS only.

Requirements

• Digitakt: core-4.0-os1.54.elemod + Digitakt_OS1.54.syx.
• Digitone: core-dn1-4.0-os1.44.elemod + Digitone_OS1.44.syx.

Highlights

• Unified DigiFilter modes on both machines: BP, BP2, COMB, TRASH, OB4, OB2.
• Digitone DigiFilter-DN: TYPE 4..9, page-2 HARM/DAMP, OB at 75% of RESO, FUNC+YES/FUNC+NO TYPE persistence.
• Filter+FX is a separate project and is not part of this release.
• The earlier mixed 1.3 draft (Digitakt 1.2 + Digitone 1.3) is archived under releases/archive/1.3-mixed/ in the repository.

Full history: CHANGELOG.md.

DigiFilter 1.2 for the Digitakt mk1 (OS 1.54) and Digitone mk1/Keys (OS 1.44).

What is in the package

• digifilter-1.2.elemod — Digitakt mk1, DigiFilter: BP, BP2, COMB, TRASH, OB4, OB2 (TYPE 8..13).
• digifilter-dn-1.2.elemod — Digitone mk1/Keys, Filter+FX: VOWEL, BANK, FOLD, CRUSH, RING, PHASER, FLANGER (TYPE 4..10).

One elemod per machine, latest OS only.

Requirements

• Digitakt: core-4.0-os1.54.elemod + Digitakt_OS1.54.syx.
• Digitone: core-dn1-4.0-os1.44.elemod + Digitone_OS1.44.syx.

Highlights

• Shared DSP layout (shared/, digifilter-dt/, digifilter-dn/).
• Digitone Filter+FX port with VOWEL/BANK AUX1/AUX2 on page 2 and TYPE persistence through FUNC+YES.
• Digitakt: OB resonance depth capped at 75% and full-cell 17x17 TYPE icons.
• DT and DN comb/UI optimizations.

Full history: CHANGELOG.md.

Wins and deltas vs the stock per-voice filter (~2400 instructions per voice per 32-frame block):

type	instructions	vs stock	MCF54418 cycles
BP / BP2 (knobs held)	1072	-55%	~1300
BP / BP2 (cutoff swept)	1635	-32%	~2250
COMB / TRASH	1693	-29%	~2020
OB4 (RESO 64)	3213	+34%	4867
OB2 (RESO 64)	3181	+33%	4948
OB4 / OB2 (zero feedback)	~1390	-42%	n/a

BP/BP2 and COMB/TRASH are now cheaper than the stock filter in every case.

DigiFilter 1.1a — a per-voice DSP performance pass, and Digitakt OS 1.54 support. The extra modes sound bit-for-bit identical to 1.1.

This release also includes 1.1 (the OB-1 modes), which was not released separately.

Performance

• BP / BP2 (state-variable filter): the coefficients are cached and rebuilt only when the cutoff/resonance move; with static knobs the block runs one 32-frame digifilter_svf call instead of four 8-frame calls. 3113 → 1229 instructions per voice per render block static (-60%), 2424 while swept (-22%) — cheaper than the stock filter when still. The audio is bit-identical.
• The SVF sample loop keeps the v1/v2 MAC chains in separate eMAC accumulators (ACC0/ACC1) so they interleave (DSPLIBUM 2.2.1.6).
• mode_coef writes c1 = k directly (exact).

OS support

• The same source tree builds for OS 1.53 and OS 1.54 (mod.json "ports" + per-OS address macros). The 1.53 build is byte-for-byte unchanged.

Filter modes (1.1)

• TYPE 8 BP, 9 BP2 — band pass
• TYPE 10 COMB, 11 TRASH — feedback combs (feedback on the RESO/GAIN knob; Harmonics/Damping on the second FLTR page's C/G encoders)
• TYPE 12 OB4, 13 OB2 — the Oberheim OB-1's 4-pole ladder and 2-pole output

Each mode uses the track's own FREQ, RESO and filter envelope; stock types are untouched.

Assets (both OS builds)

• digifilter-1.1a.elemod — OS 1.53
• digifilter-1.1a-os1.54.elemod — OS 1.54
• DigiFilter-1.1a.zip — both elemods + sources + docs + install/build README

Each .elemod needs core (elekloader) and the matching stock OS .syx.

Tested on hardware (Digitakt mk1), OS 1.53 and OS 1.54: PASS.

Credits

• Digital Alchemy DSP — BP/BP2, COMB, TRASH and the per-voice DSP/curve.
• Simon Johansson (PR #2) — OB4/OB2, the OB-1 ladder.

Full history in CHANGELOG.md.

FLTR response-curve animation rework.

• COMB/TRASH: the tooth spacing now sweeps the whole FREQ range with no dead zones (continuous step), and RESO sets the tooth depth so it rises from the floor and clamps only at the extremes.
• The displayed depth scales with FREQ/RESO directly (no curve normalisation), so turning a knob animates the curve instead of flattening it.
• BP/BP2: narrower bell (no vertical brickwall at the box edges); the peak height follows Q.
• Every curve now tapers smoothly to the floor at both ends.
• Refreshed elemod + source package and the README screenshots.

Known issue: BP (TYPE 8) can clip at high RESO near the pass-band.

FLTR response-curve and TYPE-box UI rework.

• The FLTR page's FREQ/RES response curve and the small TYPE-box glyph are now painted from a core ev_draw handler (digifilter_draw, order 40) instead of patching the page drawView vtable slot 0x401842a0. This fixes the curve being lost in multi-mod builds (core's ev_draw trampoline owned that slot once any mod subscribed).
• Fixed a latent bug where the kit TYPE slot word (type<<8) was compared raw, so the curve had never actually been drawn.
• Corrected the graph box to the stock response area (x 20..71) and removed the 0 dB baseline.
• BP/BP2: smoother bell (three [1,2,1]/4 passes over the integer/log2 result).
• COMB: real feedback-comb magnitude with evenly spaced teeth that sharpen with RESO; TRASH keeps the earlier envelope curve.
• Type box: the stock 'EQ n' glyph is masked and replaced with a fixed mini curve per mode (bell / wider bell / comb teeth / trash can).
• Refreshed elemod + source package; added filter_ui.c, the curve test, and screenshots to the README.

Known issue: BP (TYPE 8) can clip at high RESO near the pass-band.

Extra per-track filter modes for the Elektron Digitakt mk1 (OS 1.53): BP, BP2, COMB and TRASH, on top of the stock OFF / LP / HP / EQ:1..5.

TYPE	mode	what it is
8	BP	band pass (state-variable filter)
9	BP2	a wider band pass
10	COMB	feedback comb, delay from FREQ, feedback from RESO
11	TRASH	a second comb at half the delay

New in 1.0i:

• the filter envelope (FLTR slot 0x1c) now modulates the new modes exactly as the stock filter does;
• the second FLTR page drives COMB/TRASH: Base = delay offset, Width = harmonics (divider 1..4), Env Delay = damping, SRR = feedback trim;
• the DSP is optimized: no more than the stock filter's cost per voice per render block (COMB/TRASH are cheaper).

Known issue: BP (TYPE 8) can clip at some frequencies — the band-pass SVF has no output saturation. Back off RESO/ENV depth or use BP2.

Cosmetic: the FLTR page's FREQ/RES response curve still draws the stock shapes for the new types. See the README.

Assets

• DigiFilter-1.0i.zip — release package: elemods/ + sources/ (build from source) + an install/build README + LICENSE.
• digifilter-1.0i.elemod — the mod.

Needs core (e.g. core-2.1.elemod, from elekloader) and the stock Digitakt_OS1.53.syx. No Elektron firmware is included.

Work in progress. Extra per-track filter modes for the Elektron Digitakt mk1 (OS 1.53): BP, BP2, COMB and TRASH, on top of the stock OFF / LP / HP / EQ:1..5.

TYPE	mode	what it is
8	BP	band pass (state-variable filter)
9	BP2	a wider band pass
10	COMB	feedback comb, delay from FREQ, feedback from RESO
11	TRASH	a second comb at half the delay

The audio path is done and validated (with smoothing); the FLTR page's FREQ/RES response curve does not yet reflect the new types. See the README.

Assets

• DigiFilter-1.0h.zip — release package: elemods/ + sources/ (build from source) + an install/build README + LICENSE.
• digifilter-1.0h.elemod — the mod.

Needs core (e.g. core-2.1.elemod, from elekloader) and the stock Digitakt_OS1.53.syx. No Elektron firmware is included.