How the GR-300 Works

Here is a simple explanation of the genius behind the GR-300. I gleaned this information from talking to Mike Bacich, studying the GR-300 service manual, and reading the original GR-300 Patent Application.

Roland GR-300 Synthesizer Summary

Inventor: Noboru Suenaga, Fukoka, Japan

Assignee: Roland Corporation, Osaka, Japan

Application Number: 150,074

Filed: May 15, 1980

Patent Number: 4,357,852:

Application drawing of a G-303 without a Mode Switch

Patent application sketch of GR-300.

The World’s Smallest Humbucking Pickup

One Roland guitar synthesizer technology innovation is the world’s smallest humbucking pickup.

Each element in the Roland guitar synth pickup is actually a tiny humbucking pickup. As you can see, the patent illustration (on the left) depicts a classic humbucking pickup, with dual coils wrapped around opposite magnetic poles. This configuration cancels out noise while amplifying the essential guitar signal. By using tiny humbuckers, Roland was able to apply the incredible amounts of gain needed to take the tiny microvolt output from the pickups to a 25 volt, peak-to-peak signal used to directly drive the Voltage-Controlled Oscillators in the GR-300.

Interior photo of the pickup with the potted wax removed.

Adaptive Filter

Before the GR-300 can create a synthesizer waveform, the guitar input signal must be filtered to eliminate any overtones and to emphasize the fundamental tone, (or root pitch of the note). After passing through a simple low-pass filter and compression circuit, the guitar input arrives at a two-stage band-pass filter. This adaptive filter changes its frequency response curve depending on what note is played.

When notes are played from the open string to around the sixth fret, the filter takes the shape of "F1", corresponding to the fundamental of the open string. This filter attenuates 1st overtones or harmonics by 24 dB. As higher notes are played on the guitar, the filter response curve shifts to shape "F2a" and "F2b."

Square Wave to Sawtooth Wave to GR-300 Wave

	Other guitar synthesizers used different methods to try to detect the peaks of a waveform. The idea is that the time between waveform peaks will determine the pitch of the note played on the guitar. Roland took a different approach, and is probably the only company that tried zero crossing techniques to detect the pitch of a guitar signal. While it is possible to have several zero crossings in the guitar cycle (resulting in octave jumping), the adaptive filter is so efficient that this rarely happens. Here is an explanation of the diagram on the left:
Raw input guitar waveform Square wave created by processing the input waveform through filtering and zero crossing circuit. 1 uS pulses created by the leading edge of the square wave Sawtooth waveform created by 1 uS pulses. Distinct GR-300 waveform after "chopper-gate" clips the top of sawtooth waveform.
The raw guitar waveform is filtered and processed through a zero crossing detector to produce a square wave. The edges of the square wave are then used to create 1 microsecond pulses. As a pulse is received by the waveform generating circuit, a steadily rising voltage is generated by a capacitor. When the next pulse is received, the waveform resets to a value of zero, and the cycle starts all over again. Roland calls this a time-to-voltage circuit. Oscillators are tuned by varying the current to the capacitor, which controls the rate the waveform rises. This design leaves one problem: the lower the pitch of the note, the louder the note is. Notice in the example above the widest oscillator pulse (or lowest in pitch) is also the tallest (or loudest). To keep all the GR-300 notes at the same volume, the circuit uses a "chopper-gate" to basically chop off the tops of the sawtooth waveform. The result is the very distinctive GR-300 waveform, unique among analog synthesizers.

Final Signal Processing

The rest of the signal processing in the GR-300 is very much in the classic analog synthesizer design. The sawtooth oscillator outputs feed into a 24 dB per octave voltage controlled lowpass filter. At the same time, signals from the hex pickup are used to drive an envelope generator. The output of the envelope generator provides the control signals for the voltage controlled amplifier. The output from the envelope generator can also be used to modulate the voltage controlled filter, (either in regular or in inverted mode).

The final bit of genius in the GR-300 is a circuit Mark Smart describes as a "squelcher" circuit. This is a circuit designed to suppress false notes created by second harmonics. It is perhaps too complicated to summarize here, but if you would like to know more about the gory details of how the GR-300 works, there is no better resource than the GR-300 Service Manual, available from Roland. The Service Manual goes into great detail with additional diagrams and notes. My friend Mike Bacich first pointed out to me that the GR-300 technology could easily be expanded to incorporate more features, such as multiple waveform outputs, square wave, triangle, etc. Mark Smart has gone so far as to start to develop an expanded GR-300 that could be used as a controller for a more powerful analog synthesizer.

On the other hand, Roland has done a pretty good job of bringing the philosophy of the GR-300 technology back with the VG-88. Like the GR-300, the VG-88 does not really "track" in the same way that the pitch-to-MIDI devices like the GR-33, GM-70, etc. track. And the latest version of the VG-88 software, 2.0, introduces a Wave Synth algorithm which does a very good job of simulating the sound and quality of the GR-300. I do not know if Noboru Suenaga, the person credited with inventing the GR-300 is still in the business, but I want to thank him for his invention, and for all the inspiration his guitar synthesizer has given musicians around the world.


This is a picture of a clean, unprocessed D note, open string. The guitar was a G-707, bridge pickup. This was from the 1/4” output on the guitar.	This is the same note processed by a "clamped diode" circuit. Notice how the top and bottom have been clipped off. This is a classic, clean square wave.	The top trace is a VG-88 simulation of a GR-300, the bottom trace is the real thing. Aside from a slight harmonic bump in the VG-88, they are very similar.	This is waveform number 477 "GR-300 Saw 2" from the Roland SRX-07 Ultimate Keys Expansion card. This is an excellent sample of the GR-300.	This is a trace of the basic waveform from a Roland GR-33B bass synthesizer. No surprises here, the waveform is basically identical to the GR-300.

GR-300 Block Diagram:

Click on the above diagram to open a much larger picture in a new window.

GR-300 and GR-300 Alternatives

	Pat Metheny plays the G-303 and GR-300
	Brief video clip from the early nineties. Classic Pat Metheny shredding with the Roland G-303 and GR-300.
	G-303 and GR-300
	This video is a quick introduction to the sounds and features of the G-303 and GR-300. Hear samples of each of the humbucking pickups, hex fuzz, synth sounds and various other features like LFO Touch pads and Filter Modulation. The video clip was recorded with the GR-300 output going through a Yamaha 01V to add delay and reverb.
	G-707 and GR-300
	While Pat Metheny always plays a Roland G-303 controller, the distinctive sound of Pat’s guitar synthesizer can be generated with any Roland vintage G-series controller and a GR-300 synthesizer. This is a sample of a G-707 driving a GR-300, recorded through a Yamaha 01V mixer with delay and reverb added.
	GR-300 Patch on Roland Vintage Synth Card
	Guitar Synth: SR-JV80-04 Vintage Synth 144: Pats GR-300 or Roland SRX-07 Ultimate Keys. Guitar Controller: MIDI Keyboard Size: 400K Notes: Scott Summers developed this convincing GR-300 patch by sampling his own GR-300. Quite simply, it sounds great. I played these parts on a keyboard, and added delay and reverb with Digital Performer. My inspiration was "Offramp."
	VG-88 and GR-300 "Pat Metheny" Lead Tones
	Guitar Synth: GR-300 and VG-88 Guitar Controller: Ibanez X-ING IMG2010 Size: 283K Notes: First you will hear the GR-300 on the left, then the VG-88 on the right, then both together. Both the VG-88 and the GR-300 were recorded with the SBC+ at the same time through a Yamaha 01V console, with reverb and delay added by the 01V.

GR-300 Waveforms on Roland Expansion Cards

When Roland introduced the SR-JV80-04 Vintage Synth card, they included many waveforms from classic analog synthesizers, plus two distinctive sawtooth waveforms sampled from the Roland GR-300. Roland programmer and vintage GR player Scott Summers created an outstanding patch called "Pats GR-300" that does an amazing job of capturing the sound of a Pat Metheny solo.

When Roland created the new Roland SRX-07 Ultimate Keys they included all the original waveforms from the SR-JV80-04 Vintage Synth card, but reprogrammed the Pat Metheny lead as "The Real Pat." I think the original "Pats GR-300" is closer to Pat’s sound. Owners of the Roland SRX-07 Ultimate Keys card can use the included CD-ROM to re-load the original patch into their synthesizer module. I added delay and reverb from Digital Performer to try to capture the sound of Pat’s soaring solo on the title track "Offramp." It should be noted that the patch "Pats GR-300" is monophonic, and it makes very effective use of portamento and programmed pitch slides to simulate Pat’s solo phrasing.

If you want to play the demo heard above on your own synth, you can download the Standard MIDI File using the link below.

"GR-300_DEMO.smf"

Virtual GR-300 on the Roland VG-88

With Version 2.0 software, the VG-88 has a new algorithm, Wave Synth, which works very much like the original GR-300. Working side-by-side with my GR-300, I created the VG-88 patch heard above that is very close to the original GR-300 sound, and tracks equally well. The SBC+ was used so I could play the GR-300 and VG-88 at the same time. Save the file linked below, "GR300.SYX", and open it with the program VEditor. In addition patch number 1-1, "Pat G300," you will find patch number 1-2, "Slo G100," a square wave type GR-100 patch. Also, check out patch 1-4, "L/R-AG+." This is the patch I used to create simultaneous stereo acoustic and distortion guitar tones with the VG-88 in the demo files.

"GR300.syx"

Thanks again to Mark Smart, Mike Bacich and Harry Bissell for their corrections, comments and suggestions.