Russ Long, a Nashville-based producer/engineer, owns The Carport recording studio. He is a regular contributor to Pro Audio Review.
As someone who has drooled over Electro Harmonix gear since the early 1980s, I was ecstatic to see the company enter into the world of high-end studio gear. The NY-2A (PAR 7/04) and the Bi-Filter are the initial rackmount releases. The Bi-Filter is a classy, retro looking box featuring a brushed aluminum faceplate with blue and teal section panels.
Contact: Electro-Harmonix at 718-937-8300, Web Site.
Features
The Bi-Filter is a completely analog, dual-envelope and LFO-controlled filter processor with a list price of $990. The 2RU mono box has dual VCF filters that have the ability to operate in either series or parallel.
The rear panel includes eleven 1/4-inch jacks for input and output and a power jack which accepts power from the external power supply. The Audio Input jack provides the primary input to the Bi-Filter and has a maximum input signal of 6.3 VRMS (+18 dBV). The Effects Send jack provides a buffered, preamplified output of the Audio Input and the Effects Return jack provides a return from an external effects loop.
The Filter 1 and Filter 2 Outputs provide a direct output from Filter 1 and 2 respectively. The Main Output is the box's primary output and is the output of the mixer section.
The Envelope 1 CV Output provides a control voltage of envelope Follower 1 which modifies Filter 1 and the Envelope 2 CV Output provides a control voltage of envelope Follower 2 which modifies Filter 2. Both CV outputs have a range of 0-14 volts DC. The Filter 1 CV Input and Filter 2 CV Input accept a DC control voltage that controls the sweep of Filter 1 and Filter 2 respectively through their entire range. Both CV inputs have a voltage range of 0 - 5 volts. The bypass footswitch jack accepts a two-channel remote footswitch which allows the box to be remotely placed in bypass mode.
The front panel is divided into four sections. The Driver section provides the control signal sources to sweep the filters. The Filter 1 and Filter 2 sections control the Filter parameters, both filters have identical controls. The Output Mixer section provides the ability to mix both filter outputs with the input signal.
The Driver section has sliders for controlling Envelope Drive, Sweep Oscillator Rate and Sweep Oscillator Shape. The Log/Lin switch provides different dynamic response to the input signal, the Audio Boost switch allows the audio signal to be amplified according to the setting of the Envelope Drive slider and the Shape switch switches the LFO waveform to either Triangle, Square or Off. The red Over LED indicates envelope saturation.
The Filter controls include six sliders and two switches. The two Envelope Response sliders control Attack and Decay. The Envelope Amount slider controls the amount and direction that the filter is swept by the envelope follower. The Oscillator Amount slider controls the amount and direction of filter sweep by the Sweep Oscillator (LFO). The Filter Frequency slider sets the filter frequency within its operating range. Finally, the Q slider controls the filter's resonance. The Range switch changes the sweep of the filter. The Filter Mode switch selects the type of filter characteristic. It can be set to LP (low-pass mode), BP (band-pass mode) or HP (high-pass mode).
The Output Mixer section has three sliders that control the blend of Filter 1, Filter 2 and the Dry signal. In addition, the Invert 1 and Invert 2 switches invert the signal going into Filter 1 and 2 respectably. The Filter Path switch determines if the filters are running in series or parallel.
In Use
The Bi-Filter's manual includes eight basic settings which I found to be a good starting place for most sound sources. After dialing in the basic sound, it is simply a matter of finessing it into shape.
I initially put the box to work on a programmed drum machine track during a recent mix session. The mono track was uninspiring from both a sonic and performance perspective. I set the Bi-Filter up as a slow sweeping LFO and it transformed the sterile track into a phat, thick, analog track completely reviving the entire mix. On electric guitar, the box worked perfectly to create an over the top funky wah sound reminiscent of a classic Parliament track. I also had good results using it on bass guitar to create a dynamically triggered, enveloped bass sound with a massive bottom end.
In addition to bass, drums and electric guitar, I found the box to work extremely well with acoustic guitar and keyboards. My only complaint with the box is that it is not stereo. The mono box works well in most circumstances but when dealing with stereo keyboards or with a stereo drum kit, I found myself wishing that I had a stereo box to work with. The ability to have real time control of every parameter makes the box the perfect tool for the performer, remixer or DJ.
Summary
After spending several months using the Bi-Filter, I found it to be the most flexible and articulate filter that I have encountered. While it isn't the kind of device that will work on every song, when it does work, it works like a charm. The box is capable of earth shaking bottom and shimmering, transparent highs and is well worth its $990 price tag.
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