Trap Door Electronics Active Acid Analog Low Pass Filter

This is the sound of of the original Prophet 5 filter in a pedal. Active Acid, capable of transforming your instrument like few pedals can, is a powerful four-pole low-pass analog filter with an incredible amount of control available to you, the user. Equally excellent for acid house/techno, psych, and otherworldly ambient, it features envelope control of the cutoff with sidechain capability, LFO with 8 wave shapes and tap tempo, fully self-oscillating resonance that can shake your guts and shatter your teeth, external expression control, and a pre-filter overdrive to give it all some gnarl. Importantly, and often insanely, multiple things can control the filter at once. For example, the envelope follower and the LFO can both be manipulating the cutoff differently simultaneously, all while you use an external expression pedal too. That’s a lot of possibilities! Basically infinite really. 

Its heart is the beloved SSM filter found in the original Prophet-5 synth, and more than anything, Active Acid is simply a gorgeous-sounding filter pedal. With all the additional controls, it is effectively a synthesizer with your instrument as the oscillator. And yet! It’s intuitive and easy to use. 

Controls
Volume: Output level
Drive: Overdrive / Gain before the filter
Freq: Determines the cutoff frequency. Ranges from 0hz - 13.5khz
Res: Filter resonance 
Follow: Envelope filter intensity / sensitivity 
Depth: LFO intensity 
Rate: LFO speed. Ranges from .05hz - 25hz
LFO Waveshape selection: ramp down, ramp up, Square, Triangle, Sine, Scoop, Sample and Hold, Random

Switches
Envelope follower - on / off
Envelope source - internal / sidechain
Envelope response - sharp fast / smooth mellow

Other features
On board tap tempo
Expression input
Side-chain for plugging in an external trigger