Wave Sequencer

Wavestation-style wave sequencing for the Workshop Computer, edited from a Music Thing 8mu over USB MIDI host.

A sequence of up to 32 steps, where every step plays a wave from a bank of 64 single-cycle waves for a set time, at a set pitch and level, crossfading into the next step.

Three ways to use it

The card works on its own; the 8mu and the web editor are both optional.

The card picks its mode once, at power-up, so after plugging a computer in, power-cycle the module. Telling the two apart needs Computer Rev 1.1 hardware; older boards are always a USB device.

The 8mu

There are 32 steps, in four banks of eight, and the eight faders edit one bank at a time. The sequence starts 8 steps long (bank A), and its length can be anything from 1 to 32.

The four buttons are acted on when you let go, so how long you held one decides what it does:

Steps past the end of the sequence are skipped, as a step with TIME fully down is, and keep their settings, so shortening and lengthening the sequence loses nothing. On power-up, steps 9-32 start as copies of steps 1-8.

Per-step FM and SCAN multiply the panel's FM amount (X, switch middle) and wave scan amount (Y, switch middle) for each step. They crossfade from step to step along with the wave, pitch and level, so a long crossfade glides between them. A step at 0% gets no FM (or scan) at all, whatever the knob says.

GLIDE. Fully down, a step jumps straight to its pitch. Above that, its pitch slides from wherever the previous step's pitch was, starting as the step begins to be heard (the start of the crossfade into it), and taking up to the whole length of the step at the top. CV Out 1 glides with it.

GATE. Sets how long Pulse Out 1 stays high for each step, as a fraction of the step (never shorter than 5 ms, so short settings make triggers). Fully down gives no pulse at all for that step, so the page doubles as a rhythm pattern. At the top the gate stays high into the next step, a tie. The default is half the step.

Pickup. After a page change the faders don't do anything until they reach the value already stored for their step (or pass it), then take it over. So switching page never makes the sound jump.

LEDs. The 8mu's LEDs show the stored values on the current page, the playing step is lit fully, and steps past the end of the sequence are dark. On the Computer, LEDs 1-4 show which button's page is selected: lit steadily for its first page, blinking slowly for its second.

Motion. Tilting the 8mu forward and back scans every step's wave together, up to 16 waves either way. Tilting it left and right detunes Audio Out 2 by up to 50 cents. Lying flat, neither does anything. Both are gently smoothed (a lag of about 40 ms), as the 8mu sends its tilt in coarse steps that would otherwise make the scan and detune zipper.

Without an 8mu the card plays a default sequence, still under the panel controls.

Web editor

Open web/index.html in Chrome or Edge. It's a single file and needs no network. Safari and iOS can't do WebMIDI with SysEx.

Plug the computer into the Computer's USB socket with a data cable, power-cycle the module, and press Connect card & 8mu. The page reads the sequence from the card (the card is the source of truth), then sends every edit as it's made.

From the top (each section has a − button by its heading that folds it away, and + to bring it back; the browser remembers which are folded):

• Readouts. Step, pitch (as a note name), speed, crossfade, direction and whether the card is clocked, live from the card's knobs, CV and switch. While the X or Y knob on the module is waiting to pick up its setting, that setting's box has a dotted orange outline; it goes once the knob reaches the value.
• Bank, length and shift. Bank buttons, −/+ for the length, and −/+ to shift every step in the sequence one place left or right (all its settings with it, the end step wrapping round). Just above the sequence, so they stay put as the length changes.
• Sequence. All 32 steps, eight to a row. In a row with steps in the sequence, each step's width is its duration, its trace is its wave at its level, and the shaded end is its crossfade into the next; steps past the end shrink to small grey boxes, so on load there's one row of eight and three rows of boxes. The bank the faders edit has an orange box round its row. A playhead follows the card. Click a step to select it (and its row's bank).
• Copy, paste & randomise. Select steps on the sequence: click one, Shift+click a range, Ctrl/⌘+click to add or remove single steps, double-click for a whole row, Alt+click for a whole column (the same fader in every bank), or use the buttons. Copy (Ctrl/⌘+C) takes every setting of the selected steps; Paste (Ctrl/⌘+V) puts them back: one copied step fills every selected step, several fill the same number of selected steps in order, or else keep their pattern from the first selected step. Shift+paste pastes only the page the faders show. Randomise changes the wave; the wave, pitch and level; or everything (time, FM, scan, glide and gate too), of the selected steps, a row, a column or the whole sequence. Pitch stays within the spread chosen (±2, ±7 or ±12 semitones), level stays audible, and a randomised step is never skipped. Undo (Ctrl/⌘+Z) takes back pastes, randomising and shifts. The keys are listed on the page.
• Now playing. The wave being heard, including part-way through a crossfade.
• Faders. Eight pages, like the 8mu's two pages per button: tabs A, A2, B, B2... choose the page. They show the selected bank's eight steps. Drag, use the arrow keys, or double-click to reset.
• Wave bank. All 64 waves. Click one to give it to the selected step, or to every selected step.
• 8mu on the computer. Its faders, buttons and tilt drive the page, with the same pickup, banks and last-step setting as the card (the 8mu card on the right lists them). The page lights the 8mu's LEDs as the card would. A dashed line on a fader shows where the 8mu's fader is while it waits to pick up.
• Both editors at once. With the CVSeq editor open too (each Computer plugged into the computer), one 8mu drives whichever editor you last clicked in, or opened. The header shows 8mu: here or 8mu: elsewhere; clicking it, or anywhere on the page, takes the 8mu. The other page ignores the 8mu and leaves its LEDs alone, but follows where the faders are, so they pick up as usual when it comes back. Use two windows side by side rather than tabs: Chrome slows a tab that's been in the background for a few minutes.
• Inputs & outputs and 8mu. Cards on the right: every jack and what it does, and the 8mu's buttons (page, bank, last step), pickup, LEDs and tilt.
• Presets. Seven built in, plus your own, kept in the browser (localStorage), with their length. Save, update, rename, delete, and export or import as a JSON file. Loading a preset sends it to the card. Presets from before 32 steps still load, playing 8 steps with steps 9-32 as copies of 1-8.
• Direction buttons (forward, ping-pong, random) set the card's direction, and follow it when the switch is tapped. The page also shows what the X and Y knobs are doing and whether one is waiting to pick up.
• Restart and Reset (to the default sequence) act on the card too.

Without a card the page still edits, previews and keeps presets, with a simulated playhead at 1x speed.

The card and page talk SysEx; the protocol is documented in sysex.h. The card and the editor must be the same version: this one (protocol 4, 32 steps) won't talk to older firmware.

Panel

The switch's up and middle positions choose what the X and Y knobs do:

All knobs have a small dead zone at each end, so the full range is reached even if a knob doesn't quite read its very ends, and speed has one in the middle, so exactly 1x is easy to find.

Each of the four settings keeps its value. After the switch moves, a knob does nothing until it's turned to (or past) its new setting's value, then takes over, so nothing jumps. LED 6 (bottom right) blinks fast while a knob is waiting. At power-up the knobs take over straight away for the position the switch is in; the others start at speed 1x, crossfade 25%, and FM and wave scan off (so Audio In 1 and 2 do nothing until turned up).

Directions. Forward loops 1 to 8. Ping-pong plays forwards then backwards, without repeating the end steps. Random picks any other step that isn't skipped, never the same step twice in a row. After a tap, the top LEDs show the new direction for a second: one LED for forward, two for ping-pong, three for random. The web editor can set it too.

Clock divide and multiply. While a clock is plugged into Pulse In 1, the speed knob (X, switch up) stops scaling time and picks a ratio instead, in eleven equal zones round the knob: ÷8, ÷6, ÷4, ÷3, ÷2, ×1 (the middle), ×2, ×3, ×4, ×6, ×8. Dividing, a beat waits for that many clocks; multiplying, each clock is split into that many evenly spaced beats, measured from the clock and started again by every clock, so they never drift from it (and never run on past a clock that slows). CV In 2 moves the ratio two steps a volt, about an octave. The web editor shows the ratio in the Speed readout and step times in beats and clocks.

The waves

Eight families of eight, ordered so that neighbouring waves morph smoothly:

1. Additive build, sine to saw
2. Saw to square
3. Pulse width, 50% to 4%
4. Hard-sync saw
5. FM, ratio 1 then ratio 3, rising index
6. Vowel formants
7. Wavefolded sine
8. Stepped sines, then random spectra

They are generated at power-up and band-limited at three levels, chosen by pitch, to keep aliasing down on high notes.

Building

mkdir build && cd build
cmake .. && make

Needs the Pico SDK. EightMU.h and ComputerCard.h are copied from Demonstrations+HelloWorlds/PicoSDK/ComputerCard.

Not yet

• Sequences aren't saved on the card, so they're lost at power-off. Keep them as presets in the web editor and send them again after power-up.