Why It Works in a Classroom
- Every student can have it. It is free on every platform, with nothing to buy, no ads and no accounts to set up.
- Nothing to plug in. The built-in engine plays every patch; a MIDI keyboard or a DX7-family synth is optional.
- It shows what FM is doing. The Patch Builder draws the algorithm as cables between operators, and the screen above it draws the waveform each operator makes.
- 36,118 DX7 voices to take apart, the famous ones first under Essentials.
- Everything can be undone, so students can experiment freely.
Before the First Class
- Have students install Rithmatic from the App Store or Google Play.
- If you teach from a DX7 manual or book, have them open Settings › Look › Control names and choose DX7. The Patch Builder then uses the DX7's own names (BREAK POINT, KEY VELOCITY SENS, EG 1–4). SIMPLIFIED, the default, uses plain words. Either way, the ⓘ beside each control explains it and gives its other name.
- A computer keyboard plays notes:
A S D F G H J Kare the white keys andW E T Y Uthe black ones.
Finding Your Way Around the Patch Builder
- The canvas is the algorithm: each operator is a card with its LEVEL and its frequency ratio, and the cables show which operators modulate which. Carriers, the operators you hear, sit at the bottom.
- The screen above it shows the sound. Click the sliders icon beside the patch name (“Edit the voice”) and the editing tabs come out: FEEL · ENVELOPE · OPERATOR · SCALING · LFO · PITCH. The operator a tab edits is chosen with the OP menu beside the tabs, or by selecting an operator on the canvas.
- FROM SCRATCH (INIT VOICE with DX7 names) at the top of the tool column starts from the classic DX7 init voice: algorithm 1, OP1 alone as a sine.
Lesson 1: From One Sine Wave
- Press FROM SCRATCH and play. That is OP1 alone: a pure sine, with no harmonics.
- In algorithm 1, OP2 feeds OP1. Raise OP2's LEVEL slowly while holding a note. The sine fills with harmonics: that is frequency modulation. Higher level means a brighter sound.
- Change OP2's ratio from 1 to 2, then 3. Whole-number ratios stay musical; try 1.41 or 3.5 and the sound turns bell-like and inharmonic.
- Ask: what happens to the waveform on the screen at each step?
Lesson 2: Envelopes Shape the Timbre
- Keep the patch from lesson 1. Open the ENVELOPE tab and choose OP2.
- Drag the first handle right for a slow attack. Now the brightness swells in, as in a brass sound, while the volume (OP1's envelope) stays instant.
- Lower the third handle, the sustain level, so the brightness decays while the note is held: the start of a plucked or electric-piano sound.
- The four stages are ATTACK, DECAY 1, DECAY 2 and RELEASE: on a DX7, EG RATE and LEVEL 1–4.
Lesson 3: Keyboard Scaling
A patch that sounds right at middle C is often too harsh at the top of the keyboard and too dull at the bottom. Keyboard level scaling fixes that per operator, and rate scaling makes high notes decay sooner, as on a piano.
- Open the SCALING tab and choose a modulator, OP2.
- The graph is that operator's level on every key; the dotted line is where it would be with no scaling. The vertical line is the BREAK POINT.
- Drag the right side of the graph down. Play high notes: they are now darker. That is R DEPTH with a -LIN curve. Switch the curve to -EXP and the change starts gently and steepens further up.
- Drag the break point line to move the pivot, or type a note into its tile.
- Turn up RATE SCALING on the carrier and compare how long low and high notes ring.
Rithmatic names middle C C4, as most music software does. A DX7's screen calls the same key C3.
Lesson 4: Take a Classic Apart
- On Patches, press CHANGE PATCH › Essentials and pick a famous sound, such as an electric piano.
- Open the Patch Builder: the patch is on the canvas. Which operators are carriers? Which modulators are bright, and why?
- Turn operators off and on one at a time and listen to what each one adds. Look at the SCALING tab for each: most classic patches scale their modulators.
- Rebuild the sound from FROM SCRATCH, then compare.
Handing Work In
- SAVE PATCH keeps a patch in the student's bank. From the bank, EXPORT .SYX saves standard DX7 files that any DX7 editor, Dexed or a real DX7 can open.
- SHARE / IMPORT gives each patch a short code and a QR card. A student can send the code; you import it to hear exactly their patch.
- Record in the header captures a performance as a WAV.
The Two Sets of Names
| Simplified | DX7 | Where |
|---|---|---|
| FROM SCRATCH | INIT VOICE | Tool column |
| FOLLOWS (KEY / FIXED) | OSC MODE (RATIO / FIXED) | OPERATOR |
| DETUNE | OSC DETUNE | OPERATOR |
| TOUCH | KEY VELOCITY SENS | OPERATOR |
| TREMOLO | AMP MOD SENS | OPERATOR |
| ATTACK · DECAY 1 · DECAY 2 · RELEASE | EG 1 · 2 · 3 · 4 | ENVELOPE |
| PIVOT KEY | BREAK POINT | SCALING |
| LOW KEYS · HIGH KEYS | L DEPTH · R DEPTH | SCALING |
| LOW SHAPE · HIGH SHAPE | L CURVE · R CURVE | SCALING |
| FALL · FALL LATE · RISE LATE · RISE | -LIN · -EXP · +EXP · +LIN | SCALING |
| FASTER UP HIGH | RATE SCALING | SCALING |
| VIBRATO · TREMOLO | LFO PM DEPTH · LFO AM DEPTH | LFO |
| VIBRATO RANGE | PITCH MOD SENS | LFO |
Teaching with Rithmatic?
Write in. Rithmatic is made by one person, and requests from classrooms are exactly what shapes it: the SCALING tab and the DX7 names began with a teacher's email.