GR-300 Filter Pedal

-24 dB Per Octave Filter

One of the best features of the Roland GR-300 is the excellent -24 dB per octave filter. This filter gives the GR-300 much of its character, and it sounds about as good as any analog filter I have ever heard. In addition to the dramatic sweep of a -24 dB per octave filter, the GR-300 is also capable of high levels of self-resonance.

It is also very easy to expand on the range and power of the filter on the GR-300. On the rear of the GR-300 is a filter pedal input. You can plug any volume pedal into this jack, and easily sweep the filter. Some pedals work better than others, depending on your musical requirements.

How the GR-300 Filter Pedal Works

The filter pedal input works by measuring the amount of resistance in the filter pedal. The greater the resistance, the greater the range of the sweep of the filter. A typical volume pedal has a 10K potentiometer. A typical CV pedal uses a 50K potentiometer, and there are some pedals with 100K potentiometers. As you can tell by listening to the samples below, the higher the value of the potentiometer in the pedal, the greater the filter effects.

Also, the filter pedal input works in conjunction with the filter knob on the guitar. The filter knob setting on the guitar sets a "base line" that the filter sweeps from. With the knob on the guitar set to "zero," the filter pedal will sweep from a very dark sound to a brighter tone. With the filter knob on the guitar set to "5," the filter pedal will start with an open sound, and then sweep to an even brighter sound than is possible with the guitar alone.

This is an important point: you can actually extend the range of the filter on the GR-300 by adding a filter pedal. If you want really bright, screaming synth tones, or dangerously loud resonance levels, adding a filter pedal gives more range to the GR-300. Check out the GR-300 Remote Control page to see one example of using potentiometers and CV pedals with the GR-300.


Typical volume pedal	Roland EV-5 pedal	Yamaha/Korg CV pedal	GR-300 Remote Control	GR-300 Rear Panel Inputs

If you are using a volume pedal, you will plug a standard guitar cable from the GR-300 filter pedal jack to the output of the volume pedal. The GR-300 will then measure the amount of resistance from the wiper to the ground terminal. Similarly, with a Roland EV-5 Pedal, you will plug a standard guitar cable from the GR-300 filter pedal jack to the EV-5. Again, the GR-300 will then measure the amount of resistance from the wiper to the ground terminal. You will notice in the example above that the labels for "input" and "output" are switched for Korg/Yamaha CV pedal. Thus, a Yamaha pedal will not work unless re-wired to reverse connections. With a Korg EXP-2, you do not have to re-wire the pedal, since it also doubles as a volume pedal. For a EXP-2, plug a standard guitar cable from the GR-300 filter pedal jack to the output of the EXP-2 volume pedal jack.

The diagrams above are typical, but individual manufacturers may wire their products differently. If you system is not working correctly, use a multimeter to check the wiring for yourself.

Audio Samples

I recorded the audio samples below with a 10K, 50K and 100K potentiometer. Also, I did the filter sweeps with no resonance, with 50% resonance, and with 100% resonance (the resonance on the guitar at maximum). Also, the sweeps were done with the initial guitar filter setting of 0, 5 (or 50%) and 10 (maximum filter). You can hear in all these examples how the external filter pedal expands the range of the filter.

The audio samples were encoded to MP3 files at a 192 kbps settings to capture more of the high-frequency response. Also, in a few cases there is some distortion in the recording. This comes from overdriving the inputs to my mixer, usually from excessive resonance. If you are not interested in listening to the 27 samples recorded below, check out these three samples: 10K, 50K and 100K filter sweeps, all with the resonance at 100%. I think this is the easiest way to hear the difference between different control voltage pedals.

10K

Maximum Resonance

50K

Maximum Resonance

100K

Maximum Resonance

Notice how the 10K pedal does not move the filter frequency very much. The 100K really opens the filter up, but it does so too quickly. There does not seem to be any effect once the filter is open, so about half of the travel of the pedal is useless. The 50K pedal seems to be the "just right" value. It does not get quite as bright as the 100K, but overall the range is useful and effective.

Filter Sweeps with a 10K (Volume) Pedal

	No resonance	50% resonance	100% resonance
No filter	no filter no resonance	no filter 050% resonance	no filter 100% resonance
50% filter	50% filter no resonance	50% filter 50% resonance	50% filter 100% resonance
100% filter	100% filter no resonance	100% filter 50% resonance	100% filter 100% resonance

Filter Sweeps with a 50K (Control Voltage) Pedal

	No resonance	50% resonance	100% resonance
No filter	no filter no resonance	no filter 050% resonance	no filter 100% resonance
50% filter	50% filter no resonance	50% filter 50% resonance	50% filter 100% resonance
100% filter	100% filter no resonance	100% filter 50% resonance	100% filter 100% resonance

Filter Sweeps with a 100K (High Range) Pedal

	No resonance	50% resonance	100% resonance
No filter	no filter no resonance	no filter 050% resonance	no filter 100% resonance
50% filter	50% filter no resonance	50% filter 50% resonance	50% filter 100% resonance
100% filter	100% filter no resonance	100% filter 50% resonance	100% filter 100% resonance

Filter Pedal Recommendations

	Korg EXP-2 Volume/Control Voltage Pedal
	The Korg EXP-2 is a great pedal. The internal potentiometer is 50K, ideal for sweeping the GR-300. You can also use the EXP-2 as a volume pedal. The EXP-2 has three jacks: volume pedal in, volume pedal out, and CV pedal. Connect a cable to the volume pedal out jack, and you are ready to go!

	MPM VP26-U Volume Pedal
	This is my favorite pedal for flexibility. The pedal has a switch that allows it to works as either a Roland EV-5 type pedal (with a 10K potentiometer), or a Korg/Yamaha pedal (with a 50K potentiometer). However, you need to do a little soldering with the VP26-U, since the Korg/Yamaha pedals require that the tip/ring connection needs to be reversed. If you are handy, you could install a toggle switch, and use it as Korg pedal, Roland EV-5 pedal or Roland GR-300 pedal.

	Behringer Foot Controller FCV100
	This is a really, really great pedal. Built like a tank, and very reasonably priced. And, this pedal has the crucial 50K potentiometer. However, just like the MPM VP26-U pedal listed above, the tip/ring wiring is opposite of what the GR-300 needs. This pedal is not easy to re-wire on the inside, so I used an existing TRS cable and reversed the tip and sleeve connections. The pedal can also be used as a stereo pedal for keyboards and other line-level devices. This pedal does not work as a guitar pedal.