What is Synthio?

Synthio is a free online synthesizer you can play directly in your browser — no downloads, no plugins required. It uses the Web Audio API to generate sound in real time.

Play it with your computer keyboard, click the keys with your mouse, connect a MIDI controller, or tap the keys on a touchscreen. You can also slide between notes by holding and dragging across the keyboard.

Keyboard Shortcuts — Octave 1

The first octave maps to the middle and top rows of your keyboard.

Keyboard Shortcuts — Octave 2

The second octave continues across the keyboard.

Pitch Bend

Pitch bend slides the pitch of all playing notes up or down by up to ±2 semitones and springs back to centre when released. There are three ways to use it:

• 🎡
  Bend Wheel — the dark vertical strip to the left of the keyboard. Drag or touch it upward to bend pitch up, downward to bend pitch down. Release and it springs back to centre automatically.
• ⌨️
  Arrow Keys — hold ↑ to bend pitch up, hold ↓ to bend pitch down. Release the key to spring back.
• 🎹
  MIDI Pitch Wheel — if a MIDI controller is connected, its hardware pitch wheel is read in real time with full 14-bit resolution.

Controls Explained

• 🎵
  Preset — selects the instrument sound. Synth uses the oscillator engine with full control over all settings. Grand Piano, Rhodes, Wurlitzer, and Organ use real sampled recordings (loaded from the web on first use). When a sampled instrument is selected, Waveform and Detune are disabled as they only apply to the synth engine.
• 🔊
  Volume — master output level. Affects all playing notes instantly.
• 🎛️
  Waveform — (Synth mode only) changes the character of the oscillator. Sine is smooth, Square is buzzy, Sawtooth is bright and rich, Triangle is mellow.
• 🎹
  Octave — shifts all keys up or down an octave. Use the − / + buttons in the controls panel, or press the − / = keys on your keyboard.
• ⚡
  Attack — how long it takes for a note to reach full volume after you press a key.
• 📉
  Decay — how quickly the volume drops after the attack peak.
• 🔉
  Sustain — the volume level held while you keep a key pressed.
• 🌊
  Release — how long the note fades out after you release the key.
• 🎚️
  Cutoff — the lowpass filter frequency. Lower values make the sound warmer and more muffled.
• 📡
  Res — resonance of the filter. Higher values add a sharp peak at the cutoff frequency.
• 🔀
  Detune — (Synth mode only) a slightly detuned second oscillator layered on top, adding thickness and warmth.
• ✂️
  Low Cut — removes low frequencies below the set value. Useful for cleaning up bass rumble.
• 🏛️
  Reverb — adds a room or hall effect. Higher values make the sound feel more spacious.

MIDI Setup

• 💻
  Desktop (Chrome / Edge) — plug in your MIDI controller via USB and click the Connect MIDI button. It is detected automatically.
• 🎡
  Pitch Wheel — the hardware pitch wheel on your MIDI controller works automatically once connected.
• 🎛️
  Knobs (CC 14–17) — if your controller sends CC 14, 15, 16 or 17, these are mapped to Cutoff, Resonance, Detune and Low Cut respectively.
• 🤖
  Android — in Chrome go to chrome://flags, enable the Web MIDI API flag, relaunch, then connect via USB OTG adapter.
• 🍎
  iPhone / iPad — use a Lightning or USB-C to USB adapter. Safari on iOS supports Web MIDI natively.
• 📶
  Bluetooth MIDI — works on iOS with compatible controllers. Android support varies by device.

Mobile Tips

• 🔄
  Rotate your device to landscape for the best experience — the full 25-key keyboard fits on screen.
• 👆
  Tap keys directly to play. Multiple fingers work at the same time (polyphonic). Slide your finger across keys to glide between notes.
• ⚙️
  In landscape mode, tap the Settings button in the top-right of the keyboard panel to adjust all controls.
• ⛶
  Tap the fullscreen button to hide the browser UI. On Android, Add to Home Screen for true fullscreen.

Ready to play?

Jump back to the piano and start making music.