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Introduction to the GM-70:
The Roland GM-70 was the first stand alone Guitar-to-MIDI converter built by Roland. Many longtime GM-70 users insist that the GM-70 is still the best Guitar-to-MIDI converter ever built. Like other modules produced by Roland during this time, the GM-70 sports a fluorescent blue display, calling to mind high-end Lexicon units of the same period. The GM-70 is flexible and easy to use as well. This much can be said about the GM-70: no other Guitar-to-MIDI converter ever built offers as many features as the GM-70, but no other converter is as slow as the GM-70!
The GM-70 uses peak-to-peak analysis to detect pitch. This same approach is used in almost all other Roland guitar synths, except the GR-300. But Roland continued to refine this approach, and the GM-70 works much better than the preceding GR-700 or SPV-355, which used peak-to-peak analysis.
The GM-70 and GK-1:
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The GM-70 was packaged with the GK-1. This provided a complete system for any guitar player to add MIDI to his guitar rig. This was also the first time a player did not have to buy a proprietary Roland guitar to access Roland technology. The GM-70 is also missing the locking ring on the rear 24-pin connector found on the GR-100/300/700. This ring was not necessary, since the GK-1 cable used a different style of connector to securely attach to the GM-70.
GM-70 and MIDI Control:
Simply put, no MIDI converter ever built offers as many control options as the GM-70. With the GM-70 you can control up to nine possible MIDI parameters! That is four destinations for the four continuous controllers, plus two possible destinations for the mode switch. In addition, the GM-70 has inputs for two more foot switches plus a Roland EV-5 foot pedal input! And the GM-70 has a few other nice touches. The switches can be in latching or unlatching mode.
CV #3, the MIDI whammy bar found only on the Ibanez IMG2010 can be used "center" mode or "absolute" mode. In "center" mode, the whammy bar transmits values of 64 to 0 as the bar is pushed down, and values of 64 to 128 as the bar is pulled up. In "absolute" mode the whammy bar transmits values of 0 to 128, whether the bar is pushed down or pulled up. It still amazes me that the Roland GM-70 has such excellent support for the MIDI whammy bar found on the IMG-2010, but Roland never built its own guitar with a MIDI whammy bar.
One final observation: when carefully calibrating my rig, I noticed that both the GM-70 and MC-1 have a pretty coarse control resolution. Rather than seeing numbers smoothly scroll from 0 to 64, or 0 to 128, I would only see even numbers. I would have to say this indicates a lack of resolution in the GM-70 and MC-1 circuitry.
GM-70 Block Diagram:
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The Roland GM-70 compared to the Ibanez MC1:
As mentioned above, the GM-70 offers the more MIDI control than any other Guitar-to-MIDI converter. The GM-70 also lets the user pick any MIDI control destination from 0 to 95, but the MC-1 limits your options to 0 to 32. However, given the modulation flexibly of modern synths, this is not much of an issue.
The GM-70 uses the master volume control on the guitar to control both the VCAs in the GM-70, and to generate MIDI volume controller 7. MC-1 does not transmit MIDI volume controller 7 with its master volume knob. By modern standards, this seems like a problem. If you are using a IMG2010, you can assign CV #4 to controller 7 (MIDI volume). This solution will really work only with the IMG-2010, since only the IMG-2010 has CV #4 always active.
Both the MC-1 and GM-70 have rear panel analog inputs that pass through a VCA. The VCA (output) level is controlled by the master volume on the guitar controller. The difference between the two units is this: the MC-1 has two mono inputs that are summed together and passed to the mono output jack. The GM-70 has one stereo input that is passed to the stereo output. In both modules, the balance control on the guitar controls the balance from the rear panel analog inputs and the clean guitar signal generated by the pickups on the guitar. Plugging a cable into the guitar output jack removes the guitar signal from the outputs.
Finally, the MC-1 uses control knobs 1 and 2 to fine tune MIDI dynamic range and threshold, while the GM-70 has five selectable response curves. If you are not a MIDI control freak, it is hard to ignore the fact that the MC-1 is simply faster than the GM-70.
Unique features of the Ibanez MC1:
Unique features of the Roland GM-70:
Video Demos of the GM-70:
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| In this video the IMG2010 is hooked up to a GM-70, VG-88 and SBC+ 24-to-13 pin bus converter. This allows the IMG2010 to play the Roland VG-88 and use the virtual whammy bar. | |
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| In this video the IMG-2010 is hooked up to a Roland GM-70 for pitch-to-MIDI conversion. The GM-70 then drives a Roland XV-5080 sound module. | |
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| The stock "V-Guitar" patch on the VG-88 has been modified to respond to whammy bar MIDI messages from the GM-70. At the end of the clip, front panel controls are switched on for pitch and modulation. | |
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| From the original SBC+ tutorial CD-ROM created in August 2004. The tutorial covers using the GM-70 control assignments. | |
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| From the original SBC+ tutorial CD-ROM created in August 2004. After programming the GM-70, a G-303 plays a Roland XP-30 connected to the GM-70. | |
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| In this video a GK-1 is hooked up to a Roland GM-70 for pitch-to-MIDI conversion. The GM-70 then drives a Roland XV-5080 sound module. First you hear extreme synth sounds, then next patch is an expressive Soprano Sax, then finally velocity switch acoustic guitar. When playing the Ovation softly you hear harmonics, medium is standard guitar, and hard playing results in a finger slide! |
Rear Panel Connections:
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GM-70 MIDI Speed Tests:
Below are the results of MIDI speed and tracking tests I did with various guitar synthesizers. As you can see, the GM-70 was the slowest of all the processors. The complete results are on the MIDI speed test page.
GM-70: 40.39 milliseconds.
MC-1: 33.62 milliseconds.
GR-700: 29.87 milliseconds.
MKS-30 with GI-20 (GR-700) : 27.24 milliseconds.
Korg Z3: 20.15 milliseconds.
GI-10: 21.99 milliseconds.
GI-20: 19.77 milliseconds.
VG-88 (Polyphonic Pitch Transpose): 7.34 milliseconds.
VG-88 (GR-300 Simulator): 5.38 milliseconds.
GR-300: 3.32 milliseconds.
