In 1981, Roland released the TB-303 Bassline — a small silver box designed to replace a bass player during practice sessions. It flopped commercially and was discontinued within three years. Then, in the late eighties, Chicago producers discovered that when you push its Cutoff and Resonance knobs to the extreme, the machine produces a sound nobody had heard before — liquid, acidic, alive. Acid house was born, and countless techno and house classics of the following decades were built on that unmistakable squelch. Today an original TB-303 costs more on the second-hand market than many brand-new synthesizers, and even modern hardware clones are a serious investment.

That’s exactly why we built the SR-303 — a fully functional acid bassline synthesizer that runs directly in your browser. No installation, no registration, no payment. If you’ve ever wondered whether the 303 workflow is for you, you can find out in five minutes.

How does it work? The SR-303 follows the original 303 sequencer logic, which is also its secret: you don’t just program notes, you program articulation. Each of the 16 steps carries a note, octave up/down, Accent (the note hits harder and the filter opens deeper) and Slide (the note glides into the next one without retriggering — a legato glide). The interplay of slides and accents is what makes an acid line feel alive instead of static. Try it: put a slide on two neighbouring steps with different pitches, add an accent on the first step of the bar, and listen to the line start to “talk”.

The synthesis is built on the Web Audio API with attention to the details that define the sound: a saw or square oscillator, a resonant filter with envelope modulation, saturation for analog warmth, a sub-oscillator for low-end weight, and a stereo delay for space. There are four built-in preset patterns for an instant start, a RANDOM generator for inspiration, and four memory slots to save your own patterns.

And here’s the most important part — your work doesn’t stay locked in the browser. Once you’ve made a line you like, you have two options. EXPORT MIDI downloads the sequence as a standard MIDI file — with velocity data for the accents and overlapping legato notes for the slides — ready to open in your favourite software (Ableton, FL Studio, Logic, Cubase…) and play through any synth or plugin you own. And if you’re happy with the SR-303’s own sound, EXPORT WAV gives you a studio-clean audio loop (4 cycles, stereo 16-bit/44.1kHz) — rendered offline, ready to drop straight into your production or DJ set.

So before you decide to buy hardware — try it. Learn how the 303 sequencer thinks, build a few lines, export them and work with them in your studio. If you end up wanting the real machine on your desk, at least you’ll know exactly what you’re buying. And if not — you already have a free 303 in your pocket, available from any device.

SR-303 is part of the free music tools series on AICreativa.mk, alongside the SR Rhythm Sequencer.