DigiHalo

A reverb pedal for the Digitone mk1's audio inputs: twelve reverb machines (ROOM, HALL, PLATE, SPRING, SWELL, SWIRL, NEBULA, VOWEL, SHIMMER, TAPE, NONLINEAR, REFLECTIONS), each with its own DECAY range, its PARAM 1 and PARAM 2 and the rest of its parameters, HOLD as FREEZE or INFINITE on a footswitch, PERSIST, SPILLOVER, a cab filter and MIDI CCs. DigiHalo is an elekloader mod on fxkit (core-dn1 4.1).

Its MIDI CCs follow the Strymon BigSky's published CC chart (as listed on midi.guide), so a controller set up for that pedal works with it too. DigiHalo is not affiliated with Strymon and uses none of its code.

DIGIHALO is an entry in core-dn1's Mod Menu (hold a track key). While it is the active effect, DigiHalo owns the audio engine, as DigiSwarm and DigiPrism do (fxkit's core_audio owner): the synths are silent, the Digitone's own effects are off, and what you hear is the inputs through the pedal. NO turns it off and gives the audio and the screen back. The sequencer keeps running, so PLAY, STOP and TEMPO still work and PRE-DELAY can follow the Digitone's tempo. BYPASS (trig 16) passes the inputs through dry; with PERSIST on, the reverb's tail rings out.

DigiHalo 0.2 is a beta (a pre-release). It is an effect on fxkit: a MIXER on AMP (the inputs' levels and pans, as loud as the Digitone's own input), two LFOs on the stock LFO page aimed at its controls, p-locks kept in the pattern (RECORD, then hold a trig and turn a control), and MIDI hands the screen to the stock UI for the MIDI tracks while it keeps playing. Presets are gone: the project keeps its controls, mixer and LFOs, and a project saved with 0.1 opens it at its defaults. 0.2 was tested on a Digitone mk1 by its author (built before the effects' rename, which changed only names); it was also checked in digikit's emulator (digiemu) on OS 1.43 and 1.44. Not yet run on a Digitone Keys. Its source is also in elekloader, as mods/digihalo-dn1.

The screenshots are from the emulator, which has no DMA timer 0, so the C at the top right (the render's share of each block) does not read true there.

Install

The easiest way is elekloader's web page: tick DigiHalo and the + beside its Needs fxkit; the page takes the core it needs. To build it yourself you need:

• elekloader from its main branch, with Python 3.9 or newer (see its README). DigiHalo keeps 2 MB of buffers in the Digitone profile's bulk area, which the 0.4.0 app does not know: it refuses DigiHalo.
• This mod, fxkit and their core, from this repository's releases: digihalo-0.2.elemod, fxkit-0.1.elemod and core-dn1-4.1.elemod for OS 1.43, or the three -os1.44 files for 1.44. DigiHalo needs core-dn1 4.1 or newer and fxkit; every effect on fxkit (DigiSwarm, DigiPrism, DigiTide, DigiTriad, DigiReel, DigiHoard, DigiHalo) fits in one build with them.
• The stock OS file: Digitone_and_Digitone_Keys_OS1.44.syx or ..._OS1.43.syx, from Elektron's Digitone downloads. elekloader recognises the file by its hash.

Build your OS on the command line (or in elekloader's window, run from source: + Install from file... the three files and tick digihalo):

python -m elekloader.patch --stock Digitone_and_Digitone_Keys_OS1.44.syx \
    --mod core-dn1-4.1-os1.44.elemod --mod fxkit-0.1-os1.44.elemod \
    --mod digihalo-0.2-os1.44.elemod \
    --out Digitone_OS1.44-digihalo.syx --version HA02

--version is the 4 characters the unit will show. Flash the .syx with Elektron Transfer, as for any OS update: connect the unit over USB, select it in Transfer and Connect, drag the .syx onto Drop files here, and press YES on the unit. Don't turn it off until the upgrade is done.

Recovery: elekloader never changes the bootloader, so the stock OS file always restores the unit. Hold FUNC while powering on for the startup menu, and press TRIG 4 for OS UPGRADE. Then send the stock .syx with Transfer.

Opening it: hold a track key on its own for the Mod Menu, then pick DIGIHALO with its trig key (or YES). NO turns it off and gives the synths back.

0.2: on fxkit

From 0.2 DigiHalo is an effect on fxkit (../fxkit-dn1), as every effect in the build is: one at a time is active. Its Mod Menu entry makes it the active effect and opens its page; while it is active it owns the audio, page or no page, and opening another effect's entry hands that one the audio.

The p-locks are the pattern's: they are kept in one synth track's lock table (SETUP's LOCK TRACK, T4 unless you pick another), saved and copied with the pattern, and play on their steps; that track should play nothing of its own (no notes, no arpeggiator) in a pattern with DigiHalo's locks, or its trigs go astray. 0.1's presets are gone: the project keeps DigiHalo's controls, mixer and LFOs (tag DSKY, 52 bytes).

The page

DigiHalo's page is drawn like the Digitone's own parameter pages, in their fonts: the tempo in the box at the top left, the page in the title bar (page 1 is named after the machine: "Shimmer (1/3)"), the machine (two letters, with F or I while HOLD freezes or sustains, S while a swell rises, B while bypassed) and the output's meter on the left, and eight controls. While you turn a knob the title bar shows its value (the RT60, the pre-delay in ms or as a division, the interval, the vowel). LEFT and RIGHT, or PAGE, move between the pages; holding FUNC shows page 2. Pushing a knob sets it back to its default; on page 3 it steps the setting.

A knob or a parameter the machine does not have is drawn dotted. PERSIST is the shell's SETUP BYPASS setting (TRAILS or CUT): either one sets the other.

PARAM 1 and PARAM 2

PARAM 1 and PARAM 2 are fixed to two of each machine's parameters, and the rest are on page 2. LOW END is knob H for every machine.

Choosing a machine (trig, T3/T4, TYPE, CC 19) puts its parameters at their starting values; a project loaded keeps its own PARAM 1 and 2. The parameters are one set of knobs shared by the machines, not twelve sets: the project has room for the shell's 52 bytes only.

The keys

There are no presets from 0.2: the project keeps the pedal, and p-locks (RECORD) follow the pattern. The global settings are on page 3 (PERSIST, SPILLOVER, CAB) and in YES's SETUP (INPUT, CLOCK, BYPASS, MIDI CC, CC CLOSED).

The machines

All the machines but SPRING share one tank: a feedback delay network of eight lines (41-157 ms at the default sizes) mixed through a Householder matrix, each line's gain set from DECAY's RT60 and its own length, a one-pole damping in each line from TONE, and MOD moving two of the lines (one a side) a quarter cycle apart. L feeds the even lines and R the odd ones; the output is four lines a side. Before it are the pre-delay (up to 1.5 s, gliding as you turn it) and each machine's diffusers (two to five allpasses a side) and own stage; after it TONE's low-pass, LOW END's shelf (-9 to +9 dB under 250 Hz), WIDTH and the mix. The diffusers, SWIRL's and SHIMMER's stages and the tank run at 24 kHz (each two frames averaged in, and the output interpolated back up), which halves their cost; the pre-delay, the reflections, the springs, the tape, the taps and the after-stage run at 48 kHz.

• ROOM: a small tank and four early reflections a side (STUDIO, or 1.7x apart for CLUB) into the diffusers, whose strength is DIFFUSION. MOD moves the lines in its first half; in the second half it also moves the pre-delay.
• HALL: a large tank (ARENA 1.6x CONCERT), slow-building diffusion, later and softer reflections, and MID: a band from 300 Hz to 3 kHz, -12 dB to +6 dB.
• PLATE: a fast, dense build (strong diffusers) and no reflections; SMALL is splashier, LARGE smoother.
• SPRING: one, two or three springs, each a line (40-59 ms) through 14 stretched allpasses (the chirp: the drip), a band-limit and LOW END's high-pass in the loop; DWELL drives a soft-clipping preamp before them (CLEAN to OVERDRIVE). Springs 1 and 2 are panned left and right, the third centred.
• SWELL: a hall whose wet (SWELL WET) or dry and its reverb (SWELL DRY) rises over RISE TIME after every note: a note after a quiet, or one that jumps over what is ringing, starts the rise again.
• SWIRL: three long allpasses a side with feedback around them (LENGTH sizes them 0.25x to 2.5x, FEEDBACK to 0.88) before the tank, so the reverb swells and lasts past DECAY; TONE is a resonant low-pass (470 Hz - 6 kHz).
• NEBULA: the largest tank (2.6x) behind five long diffusers a side, DIFFUSION from grainy (0) to smooth; past 2:00 MOD speeds its oscillators up.
• VOWEL: a hall sung through two formant filters a side (AH, OH, OO), moving slowly between the two vowels the VOWEL parameter names (RANDOM: a new one now and then); RESONANCE their Q; MOD the singers' wander; TONE their breath.
• SHIMMER: two pitch voices (each two crossfading heads on a 64 ms sweep, at 24 kHz) on the tank's input (INPUT), its output fed back (REGEN) or both; AMOUNT their level.
• TAPE: a multi-head tape echo: 3, 4 or 6 heads, the last at TIME, evenly or unevenly spaced; FEEDBACK (the PRE-DELAY knob) from the last head (EVEN) or the last two (UNEVEN), through TONE and LOW END in the loop; MOD is wow and flutter; DIFFUSION smears the heads and sends more of them into a short reverb.
• NONLINEAR: 16 taps over TIME in a SHAPE's envelope (SWOOSH, REVERSE and RAMP rise, GATE is level and cut off, GAUSS a bell, BOUNCE the bell upside down), FEEDBACK around them, DIFFUSION after them, and a late reverb (LATE DECAY 0.3-8 s, LATE LEVEL; off at 0); MOD and MOD SPEED move the late reverb (the taps stay put: reading 16 taps between frames cost too much).
• REFLECTIONS: the image sources of a room (100 to 1000 sq ft by DECAY, SQUARE, RECT or OBLONG) around the amp at LOCATION X and Y, heard from the front: 20 reflections of the first and second order, each as late as its path is longer than the direct one, as loud as its path is shorter and the walls are hard (TONE), from its side; then a short tail. The dry follows LOCATION X across. MOD moves the pre-delay, a chorus against the dry.

HOLD sets every feedback to one and the damping and modulation off. FREEZE also stops the input reaching it: new notes play dry on top. INFINITE lets them add, and a guard on the tank's peak keeps it from running away. On NONLINEAR, HOLD holds the late reverb (at LATE LEVEL 9 when it is off); on TAPE the tape loops.

SPILLOVER off: a machine change mutes the wet for 5 ms, clears the buffers (16 KB a block, 27-90 ms) and brings the new machine in over 10 ms. On: the buffers are kept and what rings carries into the new machine's structure (no clear, the same short mute).

MIDI

DigiHalo takes its CCs (the chart below) that come on the Digitone's auto channel (MIDI CONFIG > CHANNELS > AUTO CHANNEL), through core-dn1's ev_midi_cc, while its page is open; with SETUP's CC CLOSED on, also while it is closed, and with MIDI CC on ANY CH on a track's channel too. The Digitone does not apply a CC DigiHalo takes; every other CC goes on to the Digitone. MIDI CONFIG > PORT CONFIG > INPUT FROM has to let them in.

A parameter with n steps takes 0 to n-1. CC 20 (a VALUE encoder) is not taken.

Each machine's own parameters (taken always; applied when that machine is running, as they belong to it):

Not taken: program changes and bank select (CC 0; core-dn1 passes mods the CCs only), the expression pedal (100) and its enable (60).

How it works

The render (dsp.c) runs at interrupt level in core-dn1's render, on each block of 32 frames: the machine, then the after-stage and the mix. Everything is fixed point in C, the lines holding their samples at half scale. The UI (ui.c) runs in the Digitone's UI task. Both are on the pedal shell (pedal.h, pedal_dsp.inc, pedal_ui.inc) the GAS pedals share.

• Memory: the buffers (1.1 MB: the 2.7 s pre-delay line, the tank's eight lines, 18 allpasses, three springs, the shimmer's line) are a region of the profile's bulk area (0x47900000-0x47B00000), cleared at the first five ticks after power-up. The code and its state take 37 KB of the 128 KB mods share (.run 34.6 KB, .bss 2.8 KB; compiled for size but the per-frame loops).
• CPU: in digikit's emulator (its cycle model), with the factory pattern playing and plucks on the inputs: closed, the stock render is 57% of a block; open, the synths muted, the stock part is about 17% and the whole render with DigiHalo, MOD at the top, is: ROOM 39.1%, HALL 39.1%, PLATE 34.7%, SPRING 39.2%, SWELL 35.4%, SWIRL 42.4%, NEBULA 36.7%, VOWEL 45.2% (the heaviest: two formant filters a side at 48 kHz), SHIMMER 38.6%, TAPE 40.7%, NONLINEAR 39.0%, REFLECTIONS 43.8%. DigiHalo's own share is so 18-28%. The emulator's timing assumes memory without wait states, so a unit runs slower: the shell's guard bypasses the pedal (no trails) if the whole render stays over 93% for 0.2 s, and says so in the title.
• Project data: DigiHalo's controls, its latches and SETUP, with fxkit's mixer and LFOs (fx_pack), are saved with the project (tag DSKY, 52 bytes; mods share 480 there, and the seven effects, GAIN and fxkit take about 470). The p-locks are the pattern's.

Build

python -m elekloader.sdk.build . --stock Digitone_and_Digitone_Keys_OS1.43.syx
python -m elekloader.sdk.build . --stock Digitone_and_Digitone_Keys_OS1.44.syx

It names no firmware address, so its 1.44 port is empty. It needs fxkit and core-dn1 4.1. gentables.py makes tables.h; tests.sh runs the render on a computer (the shell's host.c) and measures it with host_an.py.

Checked

In digikit's emulator, OS 1.43 and 1.44, and with the render's own code compiled for a computer and fed test signals (tests.sh, host_an.py):

• On a unit: tested on a Digitone mk1 by its author: it loads and works as expected. It is still a beta.

• The firmware. A build with the released core-dn1 3.2 and DigiHalo passes every stage of the emulator's check against stock on 1.43 and 1.44, with every screen identical.

• The probe (1.43): closed, the synths; open, the plucks through the pedal and the synths silent; the three pages, SETUP, a knob, a preset saved and recalled; T1 tapped (HOLD latched), held (HOLD while held, off on release); every machine on trig 1-12 (its flag, its sound, its render share above); T3 and T4 stepping the machine; trig 13 and 14 (HOLD latched, FREEZE); BYPASS; its CCs on the auto channel (TYPE, the knobs, SHIMMER's SHIFT 1 and AMOUNT, BOOST, PERSIST, HOLD MODE, HOLD, MIDI CLOCK, bypass) taken and set, another machine's CC taken and ignored, a CC outside the chart passed on; NO, and the synths again.

• The machines (on a computer, DECAY 64): RT60 against DECAY's (ROOM 1.76 s for 2.0, HALL 2.76 for 3.2, PLATE 2.70 for 3.2, SPRING 2.35 for 2.8, SWELL 2.29, SWIRL 3.11, NEBULA 5.67 for 7.1, SHIMMER 2.91, all within about 25% short; at DECAY 0 ROOM 0.24 s, HALL 0.59, NEBULA 1.08, SPRING 0.91); every machine at DECAY 127 on a burst decays (no runaway), SHIMMER with REGEN and IN+REG at full AMOUNT too; plucks come out within a few dB of the dry at MIX 64. FREEZE on every machine holds the level within 1-4 dB over 6.5 s (NEBULA's and VOWEL's 100 ms windows beat by up to 7 dB: a 20 s NEBULA freeze stays at -20 dB, +-1.5); INFINITE with noise pouring in stays bounded (the guard). SHIMMER on a 440 Hz sine: +1 octave puts 880 Hz at -16 dB, -1 octave 220 Hz at -21 dB, a fifth 660 Hz at -18 dB. TAPE's heads land at the last head's time / heads (3, 4, 6, uneven); NONLINEAR's six shapes give their envelopes (rising, level and cut, bell, upside-down bell); REFLECTIONS' LOCATION X moves the reflections and the dry left and right, Y from front (quieter reflections) to back; VOWEL's AAHH peaks around 1150/800 Hz, OOOO around 450/325 Hz; the PRE-DELAY and its synced divisions; LOW END's shelf, CAB's band, WIDTH, DRY, MIX's law; machine changes with SPILLOVER off and on without clicks; PERSIST's trails and a clean cut without them; T2's swell; the CPU guard's trip.

Limits

• Presets, preset names, banks, and program changes: the project keeps one, and p-locks change it on the pattern's steps.
• Twelve machines' worth of parameters at once: one shared set of knobs, set to the machine's starting values when you choose it.
• Assignable PARAM knobs: each machine's two are fixed.
• An expression pedal input, external footswitches, footswitch LEDs.
• An analog dry path and true bypass: the dry is converted, as everything on the Digitone is.
• Full-size machines: VOWEL's two formants a side and REFLECTIONS' 20 image sources are the most cut down.

Licence

GPL-2.0-or-later, as the rest of elekloader.