ChaosApe: Light Theremin-64

what it is

Play a theremin through a C64

Your phone's ambient-light sensor becomes pitch across six octaves. Wave your hand over the screen and it sings, through a 3-voice C64 SID synth engine. No light sensor? It drops straight into touch mode. Chunky terminal UI, live oscilloscope, tap any word to change it.

Tap-to-start: light = theremin, touch = notes, tap any [WORD] to change it.

Theremin-64 synth screen with oscilloscope

3-voice SID synth, live oscilloscope, LUX / FREQ / NOTE readout.

features

Light + touch play

Wave your hand over the light sensor like a real theremin, or touch to play, 1-3 fingers for chords. A SIDTAR string mode too.

3-voice SID engine

Clean-room C64 6581/8580 emulation: sine, tri, saw, pulse, noise, sub-osc, ring mod, PWM and a global overdrive.

Real .SID player

Load actual C64 .sid tunes and play them on the built-in 6510 + SID engine. Bundled with original Rev. J. Money SID jams.

Scales & keys

Ten scales (blues, pentatonic, Phrygian, harmonic minor...) plus a 12-key root selector. Pentatonic = no wrong notes.

MIDI & drums

Play .mid files through the synth, plus a SID-style step-sequencer drum machine. Import your own tunes in a tap.

Zero ads. Ever.

No ads, no pop-ups, no subscriptions, no tracking. Buy it once for $9.99 and it's yours. That's the whole deal.

help / reference

Every button, explained

The whole panel, top to bottom. Tap any [WORD] on the screen to change it, most controls cycle through their options with each tap.

Play modes tap MODE to cycle

LIGHT

The ambient-light sensor sets pitch, like a real theremin. Hold the screen to play, or turn DRONE on to play hands-free by waving. Reads room light, a window, or a flashlight.

TOUCH

Your finger sets pitch: left-right = pitch, up-down = vibrato. 1 to 3 fingers for chords. Auto-selected if your phone has no light sensor.

SIDTAR

Guitar mode. Each finger is a string (e B G D A E), sliding left-right snaps to frets, and light works a whammy bar for dive-bomb vibrato.

MIDI-IN

Plug in a MIDI keyboard or DAW and it plays the voices directly. Shows up automatically when MIDI is connected. A footpedal can be assigned (see PED).

Playing controls

DRONE

Bottom-right corner, LIGHT mode. ON = hands-free, wave to play with no touch. OFF = hold the screen to make sound. Turn it on for true theremin hand-waving.

SCALE

Snaps your pitch to a scale so you stay in tune: OFF (smooth glide, no snap), CHROM (all 12 notes), MAJOR, MINOR, MAJPENT, MINPENT, BLUES, DORIAN, PHRYG (Phrygian), HARMMIN (harmonic minor). Pentatonic = you cannot hit a wrong note.

KEY

The root note the scale is built on, C through B. Pick E for E-blues, A for A-minor, and so on.

OCT

Octave shift for the whole instrument: -1, 0, +1, +2. Drop it for deep bass, raise it for leads.

DET

Detune. Spreads the three voices slightly apart for a thick, chorused, analog feel. OFF gives pure tones.

Voices & tone

V1 / V2 / V3

Three independent oscillators. Tap each to pick its wave: OFF, SINE, TRI, SAW, PULSE, NOISE. Turn on two or three for chords and fat layers, or one for a clean lead.

SUB

Sub-oscillator. Adds a sine one octave below for weight and bass. On by default.

RING

Ring modulation. Multiplies the voices for metallic, bell-like, clangy tones.

PWM

Auto pulse-width modulation. Slowly sweeps the PULSE wave's shape for a moving, shimmering tone. Affects the PULSE wave only.

DIST

Global overdrive, top-left: OFF, LO, MID, HI. Adds grit and crunch; HI clips hard and square for aggressive tones.

SID player & drums

[SID]

Opens the Commodore 64 tune player. Loads real .sid files and plays them on the built-in 6510 CPU + SID chip emulation. Comes with original Rev. J. Money SID jams, and you can open your own .sid files.

[DRUM]

A SID-style step sequencer: 4 tracks (KICK, SNARE, HAT, PERC) across 16 steps. Tap cells to build a beat, then PLAY/STOP, set BPM, or CLEAR. "SYNTH >" returns to the instrument.

SYNC / CONCERTO

Optional. Two or more phones on the same WiFi or hotspot auto-lock their beats together for a jam. Stays entirely on your local network, nothing goes to a server.

MIDI pedal PED, MIDI-IN mode

SUST

Sustain, holds notes while the pedal is down.

WHAM

Whammy, press to dive the pitch down up to a full octave.

OCT+

Jumps up an octave while the pedal is held.

DIST

Pushes the overdrive harder the more you press.

VIB

Adds vibrato depth with the pedal.

Pro tips

Play with a flashlight. A second phone's torch moved closer and farther sweeps a huge, smooth range, far more control than waving a hand.
Set SCALE to a pentatonic and you literally cannot play a wrong note. Perfect for jamming or handing the phone to a kid.
Headphones or a Bluetooth speaker reveal the sub-bass the tiny phone speaker can't push.
Everything on screen is a button. If you see a [WORD], tap it.

see it play

Yes, it really makes music

Here's Fur Elise, three voices, played by waving light over the phone.

Full Fur Elise, three voices (sine, triangle, saw), sub on.

closed beta

Now in testing

Theremin-64 is in invite-only testing on Google Play before its public launch. Testers play early, free, and help shape the final release.

Join the test

Tap Join the Beta Test and accept, signed in with the Google account you were invited with. Not invited yet? Email me your Gmail.

Install it, free

Install straight from Google Play on that same account. No code to enter, nothing to buy, invited testers install at no charge.

Play & tell me

Mess with it and send honest feedback. Updates arrive automatically as I ship fixes.

About that payment screen

Theremin-64 will be $9.99 when it launches to everyone. As a beta tester, you get it free. There's no promo code to redeem and nothing to purchase.

Because it's a paid app, Google Play may still flash a price or ask about a payment method while you install. That's just how Play handles paid apps during testing. You will not be charged. Continue on through and it installs.

If it ever actually tries to bill you, stop and email me, it just means your Gmail isn't on my tester list yet, and I'll add it so it's free.

How to be a great tester

Leave feedback on the Play listing first. On the Theremin-64 store page, scroll to Rate this app, tap the stars and add a couple sentences. As a tester it stays private, and it shows Google the app is being actively tested, which is what lets me launch it.
Actually play with it. Try light mode and touch mode, in bright light and in the dark, on the speaker and on headphones. Push it and see what breaks.
Report bugs clearly. Tell me what happened, your phone model and Android version, and how to make it happen again. A screenshot or screen recording is gold.
Say what you really think. What's fun? What's confusing? Blunt beats polite, I can't fix what I don't hear about.
Stay opted in. For this launch Google needs at least 12 testers opted in continuously for 14 days, so please don't leave the program during that window.
Reach me anytime. For anything with a screenshot or a back-and-forth, email myemail937@gmail.com.

private by design

No accounts

No sign-up, no login, no profile. Open it and play.

No tracking, no ads

No analytics, no ad networks, no data collection. Nothing about you is gathered or sold.

Stays on your phone

The only network use is the optional CONCERTO mode, two phones on the same WiFi syncing their beat directly to each other. Nothing goes to any server.