A polyphonic subtractive synth that runs entirely in your browser. Pick a preset or build your own sound with two oscillators, an ADSR envelope, a resonant filter, an LFO, drive and delay, then play it with your computer keyboard, the mouse, touch or a MIDI keyboard and record the result as a WAV file.
Last updated:
Click a key or press Z, X, C… to play
C3 – C6
Keyboard: Z–M lower octave, Q–U upper, hold Space for sustain, ←/→ octave.
Press Record, play something, then press Stop.
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How to use the Online Synthesizer
Click a key on the on-screen keyboard (browsers need one click before they make sound), or type on your computer keyboard: Z to M is the lower octave, Q to U the next one.
Choose a preset from the list, or press Generate random patch for a surprise.
Shape the sound: set the oscillator waveforms, move the filter cutoff and resonance, change Attack and Release, and route the LFO to pitch, filter or volume.
Connect a MIDI keyboard with the Connect MIDI button to play with velocity, sustain pedal, pitch bend and mod wheel.
Press Record, play, then Stop. Play it back or press Download WAV to save the audio.
Save preset stores your patch in this browser so you can pick it again later.
How subtractive synthesis works
This synth follows the classic signal path found on most analog and virtual-analog synthesizers: oscillators → filter → amplifier, with an envelope and an LFO that move things over time.
Oscillators make the raw tone. A sine wave has no overtones and sounds pure; a triangle has a few soft odd harmonics; a square has strong odd harmonics (hollow, woody, chiptune); a sawtooth contains every harmonic and sounds bright and buzzy, which makes it the favorite starting point for leads, brass and strings.
Detune is measured in cents (1/100 of a semitone). Setting the two oscillators a few cents apart makes them drift in and out of phase, the thick "chorus" sound of supersaws and string pads.
The filter removes part of the spectrum. A low-pass filter lets frequencies below the cutoff through; raising resonance adds a peak at the cutoff that gives the typical "squelchy" synth sound. Env amount sweeps the cutoff up (or down) by that many octaves with the same envelope as the volume.
The ADSR envelope shapes the volume of each note: Attack, Decay, Sustain level and Release.
The LFO (low-frequency oscillator) is a slow wave below about 20 Hz. On pitch it gives vibrato, on the filter a "wobble", on volume a tremolo.
Recipes for common sounds
Sound
Oscillators
Filter
Envelope
Bass
Saw or square, octave −1
Low-pass 300–700 Hz, resonance 4–8, env +2 to +3 oct
Fast attack, short decay, sustain 30–60%, short release
Attack 0.5–1.5 s, release 2–3 s; slow LFO on the filter, delay on
Pluck
Triangle + saw
Low-pass 500–900 Hz, env +3 to +4 oct
Attack 0, decay 0.3 s, sustain 0
Organ
Sine + sine one octave up
Wide open
Instant attack, full sustain, very short release; LFO tremolo 6 Hz
Note frequencies
The synth uses twelve-tone equal temperament tuned to A4 = 440 Hz. The frequency of MIDI note n is f = 440 × 2(n − 69) / 12, so each octave doubles the frequency and each semitone multiplies it by about 1.0595. Oscillator octave settings multiply the frequency by 2 per step, and a detune of c cents multiplies it by 2c / 1200.
Frequently asked questions
What kind of synthesizer is this?
It is a subtractive synthesizer, the classic analog-style design: oscillators produce harmonically rich waveforms, a resonant filter removes part of the spectrum, and envelopes and an LFO move the volume, cutoff and pitch over time. It is built on the Web Audio API, so it runs locally in your browser without plug-ins.
How do I play it with my computer keyboard?
The bottom letter row Z X C V B N M plays the white keys of the lower octave (S D G H J are the black keys) and the top row Q W E R T Y U plays the next octave up (2 3 5 6 7 are the black keys). Hold Space for sustain and use the Octave buttons to move the range.
Can I use a MIDI keyboard?
Yes, in browsers with Web MIDI (Chrome, Edge, Opera and Firefox). Plug in the keyboard, press Connect MIDI and allow access. Note velocity, the sustain pedal (CC64), the pitch bend wheel (plus or minus 2 semitones) and the mod wheel (extra vibrato) are supported. Safari does not support Web MIDI.
What do Attack, Decay, Sustain and Release mean?
Attack is how long a note takes to reach full volume, Decay is how long it then takes to fall to the Sustain level, Sustain is the level held while the key stays down, and Release is how long the note takes to fade after you let go. Short attack and release give plucks and stabs; long ones give pads.
How do I record and save my playing?
Press Record, play, then press Stop recording. The exact audio output, including filter sweeps and delay, is captured in real time. Press Play to listen and Download WAV to save a 16-bit stereo WAV file. Silence before the first note is trimmed automatically.
Why is there a delay between pressing a key and hearing the note?
Most of the latency comes from the audio output of the device. Wired headphones or speakers are faster than Bluetooth, which can add 100 to 300 ms. Closing other audio apps and using a desktop browser also helps.
Are my presets uploaded anywhere?
No. Sound is generated on your device, and saved presets and your last patch are stored only in this browser's local storage.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.