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Acid Diode Ladder Filter

Transistor Filter

Primal Audio I/S

  • • Industrial circuit simulated 303 filter

Audio examples

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.

ACID is included in our FILTER CLASSICS bundle.

Product details

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.

Warning: ACID is very demanding CPU-wise! We’ve used every possible trick to reduce the CPU usage, however, great sound doesn’t come for free.


  • LOW-PASS FILTER: 24dB/oct squelchy low-pass filter based on the TB-303 diode ladder filter circuit
  • ENVELOPE FOLLOWER: Envelope Follower with external side chain for organic filter modulation
  • INDUSTRIAL CIRCUIT SIMULATION: We use techniques from industrial circuit simulators to accurately model the electric components

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.



Released: 2016-02-01
Version: 1.0.0