sound engines

Low-pass filter

24dB/oct squelchy low-pass filter based on the TB-303 filter circuit

Multimode mixer

Envelope Follower

Envelope Follower with external side chain for organic filter modulation

Circuit Simulation


We use techniques from industrial circuit simulators to accurately model the electric components

Undiluted analog corrosion

ACID is an analogue-modelled low-pass filter. Based on the characteristic diode ladder filter design from the vintage Roland TB-303 synthesizer, ACID brings the squelchy sound of the original unit to the Reason Rack. ACID uses cutting-edge DSP rooted in techniques used in industrial circuit simulators to accurately model its analogue components. Furthermore it extends the original filter with an envelope follower, resulting in a versatile unit capable of many types of effects from gentle overdrive and adding some bite to samples to transforming dull synth sequences into bubbly, acidy riffs.

Download on teh

Read the ACID manual

Audio demos

Sheer Analogue Authenticity

In order to faithfully capture the analogue character of the original filter we have modelled the behaviour of its electric components by bringing techniques from industrial circuit simulators (e.g. SPICE) into the domain of real-time audio processing. A topology-preserving, zero-delay feedback loop resolved by a heavily optimised differential solver ensures that the sheer authenticity of the analogue sound is preserved and raises the bar for sonic realism to a level unseen in the Rack Store.

Everybody Needs an ACID

Introduced in 1982 the Roland TB-303 Bass Line synthesizer was originally made to provide bass-line accompaniment to guitarists/keyboard players. While not a successful product in its time it had a defining role in the development of house music, influencing Chicago house which also formed the basis for ACID, house, techno, and trance. Still today it is one of the most sought after vintage synths ever and is particularly famous for its unique and distinctive filter. It has been used by a multitude of artists including Aphex Twin, 808 State, Future Sound of London, Massive Attack, Orbital, Eat Static, Norman Cook (Fatboy Slim), Air, Astral Projection, Josh Wink, Plastikman, √úberzone, Moby, Hardfloor, Ultramarine, Underworld, BT, The Prodigy, Jimmy Edgar, Union Jack, Front Line Assembly, Pet Shop Boys, Freddy Fresh, Luke Vibert, and the Chemical Brothers.

All product names used are trademarks of their respective owners, and reference to these here in no way constitutes an association or affiliation with Primal Audio. All trademarks are solely used to identify the products whose sound was studied during the development of ACID.