Bi-Filter

Rackmount Dual Analog Filter Processor
Multi-mode filters and an all-analog signal path pumps up your sound with the world's fattest, sweetest filter power. Two separate filter sections can be used in serial or parallel with different tonal sweeps, which react individually or interactively. Phase control allows for further contouring. Individual outputs for each filter plus a mixed output. In addition an external CV in or Expression Pedal in for controlling the filters with external devices, footswitch pedal input and two CV outputs enable audio triggering from each filter.

"The Bi-Filter has the flexibility and power to take your tracks to analog heaven." -- Mitch Gallagher, EQ Magazine

"The Bi-Filter's tone lives up to Electro-Harmonix's goal of exquisiteness. Its fluid, organic sound was punchy while producing floorboard rumbling lows and sweeping highs." -- Doug Eisengrein, Electronic Musician


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Quick Specs
True bypass using a mechanical relay
All analog processing
Dual 2-pole resonant filters
Each filter completely independent from the other
Switchable filter type for each filter: lowpass, bandpass or highpass
Accurate envelope follower section using a precision full-wave rectifier circuit with optional log control
Dual attack and decay adjustability for the envelopes each filter
LFO with switchable triangle or square wave shape
LFO duty cycle adjustable from 0 to 100% or from up sawtooth to down sawtooth
Switchable FX Loop section allows user to apply effects to the signal before the filters while retaining the instrument's original dynamics
FX Loop section also allows the envelope of one instrument to sweep the filters acting on another instrument
Independent outputs of each filter
Mixer section allows user to mix the filter outputs with the dry signal as well as invert each filter
CV/expression pedal inputs for each filter, controlling the center frequency of the respective filter
CV outs output each filter's envelope section
18VAC-1000 power supply included
From the Blog
Posted 6/18/2009
Can you crack the code of Riddle & Enigma?

First clue: Mike Beigel landing EHX color in the remote ice fields of Cape Crozier, Antarctica.

Years earlier, back in 1972, Mike also explored new sonic landscapes as inventor/engineer of the world's first stand-alone envelope filter, the Mu-Tron III. The sound was quickly captured by Stevie Wonder, and made famous by his 1973 funk classic, "Higher Ground."

Here's a vintage 1973 performance:

Despite Stevie's personal endorsement (see right) and other noteworthy users like Bootsy Collins and Jerry Garcia, the maker of the Mu-Tron III (Musitronics) closed shop in 1978. Years later, Mike Beigel decided to bring the original Mu-Tron III mojo over to EHX. Mike picks up the story:

"In '94 I met [EHX founder] Mike Matthews at a NAMM show. We talked about effects pedals, and later he asked me if I'd be interested in re-creating the Mu-Tron III for Electro-Harmonix. The new box which is called the Q-Tron, uses the same opto-electronic design of the Mu-Tron III, with new features and improved specs."

Mike and Mike went on to design the EHX Q-Tron, Q-Tron Plus, Micro Q-Tron, Stereo Polyphase, Bi-Filter -- and now, Riddle & Enigma: mysteriously musical envelope filters for guitar and bass.

What about Antarctica? In that same year (1994) Mike Beigel was also hired to design and build a system to track penguins between their nests on the beaches of Antarctica and their aquatic feeding territories. Mike later traveled to Antarctica to install and troubleshoot his system, and remembered to pack his EHX t-shirt. Mike adds: "And yes, I did work on some EHX designs during my spare time in Antarctica!"

While there, Mike also managed to capture amazing photos of the locals:

Riddle & Enigma: welcome to the family.

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