SOUND EXAMPLE

EXTENDED OVERVIEW

There is not one facet of audio electronics more understated than that of the humble filter. Whether you know it or not, filters are one of the fundamental building blocks of guitar effects. From the simple low-pass filter included with every Rat circuit to the Moog “ladder filter” circuit that once defined electronic music, filters are everywhere.

One of the coolest bits about the humble filter is that many examples aren’t so humble. Partswise, the aforementioned circuits have three and ~50 pieces respectively—the Moog circuit isn’t even the most complicated of the bunch. And there are far more types of filters than one might expect, along with orders of gradual intensity.

Audio filters first arrived on the working guitarist’s pedalboard in the ‘70s when Seamoon released its Funk Machine, packaged in the form of an envelope-controlled effect. Mike Beigel’s Mu-Tron III followed shortly after, utilizing a bipolar-powered state-variable filter straight out of an engineering textbook but with the added twist that it was also envelope controllable.

As it turns out, state-variable filters are an excellent jumping-off point to building one’s own audio filter, and so today we humbly offer up a stripped-down state-variable low-pass filter. Of the three main filter “-pass” types of filters, low-pass is perhaps the most recognizable. The filter rejects frequencies higher than the adjustable cutoff point, resulting in a slick, studio-quality effect.

Of course, the “Filter” control in the Rat is also a low-pass filter, but it’s an extremely simple passive affair and so the attenuation is not as steep and as a result, the sound is not quite as dramatic as that of the state-variable design.

Our Filter kit puts this synth-like control right at your feet, giving you a Resonance control (also known as “feedback”) for a more intense filtering experience, as well as an onboard Gain control to add some grit to the signal. This kit sounds absolutely dynamite when stacked with your favorite dirt box. You’re going to love this one.

CONTROLS

FILTER:  Selects the cutoff frequency of the low-pass filter. At one end, the cutoff frequency is about 9KHz, and the other end drops it down to 280Hz.

GAIN: This is actually a potentiometer in series with the input, which works the same as your volume control on your guitar. If you plan on running the Filter first in your chain, you can leave this knob cranked and use your guitar’s volume in its place. Integrating this pedal on a pedalboard will require a little finer adjustment.

RESONANCE: This introduces feedback into the circuit to make it more “synth-like” in the simplest possible terms. When it is all the way down, you get some tame but still present filtering. As you turn the knob up, the filtering becomes more and more intense, with the maximum sounding very “juicy”. If you’ve dealt with some of the more intricate synth filter designs in the past, you may be asking yourself if cranking this control will cause the filter to oscillate. It will not.