ACID-O
A growling, analog-dirty acid bassline synth — built by Mad House Audio
ACID-O is a TB-303-style acid bass synthesizer engineered to sound like real analog hardware misbehaving in exactly the right ways — croaky, unstable resonance instead of a clean digital whistle, and a genre-aware brain that writes musical basslines instead of random noise.
Having trouble installing?
Installing ACID-O
You might see a security warning from macOS or Windows the first time you install ACID-O. This is completely normal and expected — it happens because ACID-O is independently developed software, and both operating systems automatically flag any app that hasn't paid for their official developer certification program. It doesn't mean anything is wrong with your download.
Follow the steps below for your operating system and you'll be up and running in under a minute.
macOS
After downloading, you may see a message saying "ACID-O can't be opened because Apple cannot check it for malicious software."
Locate the downloaded file (usually in your Downloads folder)
Right-click (or Control-click) on it
Select Open from the menu
A new dialog appears — click Open again to confirm
That's it — this only needs to be done once. After this, ACID-O will open normally every time.
Didn't see that menu, or missed it? Go to System Settings → Privacy & Security, scroll down, and look for a message about ACID-O being blocked, with an Open Anyway button next to it.
Windows
After downloading, you may see a blue screen from Windows Defender SmartScreen saying "Windows protected your PC."
Click More info (small text link under the main message)
Click Run anyway
The installer will then run normally. You only need to do this once, during installation.
Using Chrome or Edge and see a download warning first? Click Keep (or More info → Keep anyway) to finish the download before opening the installer.
Is this actually safe?
Yes. These warnings exist because both Apple and Microsoft charge developers for a certification/notarization process, and as a new, independent plugin company, we haven't gone through that yet. The warning is about unfamiliarity, not a detected problem — it's the same message you'd see installing software from any small or independent developer.
If you'd rather verify things yourself before proceeding, feel free to scan the downloaded file with your antivirus of choice — we're happy to have you double-check.
Still stuck?
Email us at [support@madhouseaudio.com] with a screenshot of what you're seeing and we'll get you sorted quickly.
The Sound Engine
Dual parallel filters (Filter A / Filter B) — nonlinear diode-ladder-style filters. Route each oscillator independently into Filter A, Filter B, or bypass both entirely for a dry signal straight to the mix.
Real analog character, not a clean digital clone — cutoff response has natural inertia instead of snapping to modulation with robotic precision, resonance strength shifts with cutoff frequency the way real circuits behave, and a slow, subtle drift keeps the resonant peak from sitting on a dead-static pitch. Saturation is applied at the actual output stage, not just buried in the feedback path, so the grit is genuinely audible, not just theoretical.
Two main oscillators + a dedicated sub — Saw/Square/Sine/Triangle waveforms, each with independent Level, Detune, Phase, Pan, and a Latency control for Haas-effect stereo widening.
Master section — Tune, Decay, Slide Time (that signature 303 portamento glide), Accent, and Volume.
Built-in limiter with threshold control and input/output/gain-reduction metering, so you can push the filter hard without worrying about your master bus.
Modulation
2 LFOs + 2 Envelopes, freely drag-and-drop routable onto virtually any knob in the plugin.
Custom breakpoint editor — draw your own LFO shapes with up to 16 points, not just stock waveforms.
Tempo-synced or free-running, with retrig options and host-locked phase.
Visual routing feedback — colored arcs directly on each knob show you exactly what's modulating it and by how much, at a glance.
The Sequencer
64 steps across 4 pages, with per-step control over note, octave, gate, accent, slide, and tie — every classic acid articulation.
Swing, adjustable clock rate, and full BPM sync or free-running operation.
Scale-aware note display with a sharps/flats toggle, so the sequencer always shows you musically sensible note names.
The Randomizer — Actually Musical
This is where ACID-O earns its "genre-aware brain":
Five genre profiles — Acid House, Tech House, Afro House, Techno, and Deep House — each with its own character baked into cutoff ranges, resonance, envelope timing, and rhythmic feel.
Key- and scale-aware melody generation. Lock the randomizer to a specific key and scale, or let it pick a fresh one on every randomize — either way, melodies use weighted stepwise motion and motif reuse to sound like an intentional bassline, not scattered notes.
Musically-constrained harmony — when a second oscillator is detuned for a fuller sound, it only ever lands on a unison, octave, or perfect fifth (and only when that fifth is actually in the current scale), so layered oscillators never clash.
Respects your work — lock any panel to protect it from randomization, and the randomizer only touches oscillators and modulation targets that are actually switched on.
Interface
Live animated waveform displays on every oscillator and the master bus — real audio-reactive visual feedback, not a decorative animation, showing you exactly what's sounding and how loud, in real time.
Distressed yellow-and-black hardware aesthetic with skeuomorphic knobs and sliders styled after well-worn analog gear.
Adjustable UI scale from 50% to 200% for any screen size.
Built-in onboarding walkthrough for first-time users.
Compatibility
Formats: VST3, AU, Standalone
macOS: 11 (Big Sur) or later, Apple Silicon & Intel
Windows: 10 or later, 64-bit
Works in any VST3/AU-compatible DAW — Ableton Live, FL Studio, Logic Pro, Cubase, Reaper, Studio One, Bitwig, and more.
Soinc madness, engineered.
