Reverse engineering GK3 for specific MIDI output application, help needed please

Started by raccio14, April 12, 2016, 05:19:09 PM

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raccio14

I'm a 5th year Electrical Engineering student at Georgia Tech, working on my senior design project.  Roughly, the idea of the project is to use the data from a hexaphonic pickup to create a program to automatically output a tab of what a guitarist is playing, ideally as close to real time as possible.   

Given that the hexaphonic pickup is capable of providing analog sound signals from each string separately, the idea is as follows:   
The data from each string will be read separately as frequency and duration data for each note.   By knowing the frequency of the note, and the string that it was played on, the position of the guitarist's fingers can be extrapolated.   If need be, additional capacitive sensors will be placed along the neck of the guitar for confirmation of hand position to assist with error correction. 

Currently the team has decided upon trying to use a Roland GK-3 pickup and making our own circuit to interpret the output.   My problems are as follows:

Is there a good way to convert the analog sound information from the GK3 into MIDI information that can be fed to the computer?   If we can use MIDI information, frequency data will be readily available and should assist in the programming.   

Additionally, how is the GK3 unit powered?   I've found the circuit schematic on the forums, but it seems incomplete: https://www.vguitarforums.com/smf/index.php?topic=4729.0

I've explored a bunch of the breakout boxes on Bill Bax's website, and it seems that he and other members here have access to schematics for the GK3 and related accessories.   Currently, I think that the best way to do this would probably to use a breakout circuit to split the 13-pin cable to 6 buffered outputs, similar to some of the breakout boxes that you have.   Each of these signals will need to be fed to separate MIDI converters (or one multiplexed, if possible), so that frequency, envelope, and string number data can be fed to the computer for the program to analyse.   
Ideally, this would all be simulated on a circuit level, and a custom PCB will be printed for our conversion unit with USB or MIDI output. 

If you have any suggestions on the best way to make this happen, I'd greatly appreciate it.   Any circuit schematics, specifications, or other tips/tricks you have involving the GK-3 and related accessories are definitely needed. 

Really the things I'm trying to figure out now are:

1.  How power the GK3 and start reading analog signal data out of the 13 pin DIN, like with a scope.
2.  Buffering that data and turning a copy of it into MIDI (schematics from the GI-10 would probably be helpful for this)

Thanks!


HAMERMAN409

A GK-3 is normally used in conjunction with a device (GR-55, GR-33, GR-30, VG-99) that would feed it power.

To do what you want with minimal hardware you probably want to connect the GK-3 to a 13 pin DIN connector using a Roland 13 pin hex cable. You would then have to provide +7V and -7V power to the DIN connector to power the GK-3. You could feed each of the six string output signals into 6 different channels of a sound card. You may need to add some gain to each of the six signals. When processing keep in mind that any given string signal may (and probably will) have some signal from the adjacent string on it.

gumtown

You might want to have a look at the Fishman Triple play, it is a hex pickup, hex2midi converter, and wireless to USB receiver dongle.
It already does much of what you are wanting to achieve.

Otherwise, the GK 13 pin system uses the shield (outer shell) for a common ground,
pins 1~6 are the strings 1~6,
pin 12 requires +7 volts,
pin 13 requires -7 volts
(0 volts is common to ground).
You might be able to build something using an Arduino,
it does 10 bit A/D, but midi notes only require 7 bit, the Teensy 3.2 should be plenty powerful enough.
If you want to power a GK-3 from single source supply (a battery cell), then one of these will provide the split rail supply
http://www.ebay.com/itm/3W-DC-Boost-Converter-3-3V-10V-to-12V-Step-up-Power-Module-replace-LM78XX-79XX/301906594702?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D36213%26meid%3D0e20a2a8f8d9422192307abf9e7f3ce4%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D201413161834
by adding a 6.8 k ohm resistor from the + output back into the circuit, it will give you +7 and -7 volts


I have (long time ago) done pitch to midi conversion with a micro, use the analog input to measure amplitude and trigger threshold, and also boost the input signal to square wave and use digital inputs to measure duty cycle (i.e. the note pitch).
That should give you half cycle note detection (minus string attack transient peaks).
Free "GR-55 FloorBoard" editor software from https://sourceforge.net/projects/grfloorboard/

GraemeJ

Quote from: raccio14 on April 12, 2016, 05:19:09 PM
Is there a good way to convert the analog sound information from the GK3 into MIDI information that can be fed to the computer?   If we can use MIDI information, frequency data will be readily available and should assist in the programming.

If this is purely an engineering exercise, then have fun.  Otherwise, it seems to me, you are trying to re-invent the wheel.

The raison d'être for the hex pickup is to provide midi information.  The analogue signals are converted to midi within a dedicated synthesiser (roland GR 33, for example) or by a separate unit (Roland GI 20, for example) whose output can be use to control any midi sound engine.

There already exists software that will convert midi to tab (https://midi-to-tab.com , for example).

gumtown

An interesting project/concept, would be to do the opposite and build a device which can transcribe midi file guitar parts to a hex analog signal which can be passed into a GR/VG unit, as a replacement for the guitar and GK pickup.
Free "GR-55 FloorBoard" editor software from https://sourceforge.net/projects/grfloorboard/

admin

QuoteAn interesting project/concept, would be to do the opposite and build a device which can transcribe midi file guitar parts to a hex analog signal which can be passed into a GR/VG unit, as a replacement for the guitar and GK pickup.

A few of us were doing just that back in 1997 , play any 6 tracks of audio (could be from MIDI triggered soft synth)  out a multi channel PC/Mac audio interface feeding the RMC Fanout box which feeds the GK Input on a VG-8.
http://www.rmcpickup.com/fanoutbox.html


but back to the topic

I understand the goal is a learning exercise
read the MIDI Guitar FAQ by  guru Andras Szalay ( inventor of Shadow GTM-6, Axon AX100, Fishman Tripleplay)   
http://www.panda-audio.com/midiguitar.php

and read patents
http://www.google.com/patents/US5033353

https://www.google.com/patents/US7732703?dq=midi+guitar&hl=en&sa=X&ved=0ahUKEwjay7qx64vMAhVCKWMKHcWcCNUQ6AEIOzAE
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admin

Also there is a global abundant mis understanding of what the GK-3 does what format signals are contained in the GK 13 pin cable

Read
How a "13pin MIDI Cable" destroyed the Roland V-Guitar DSP Modeling brand
https://www.vguitarforums.com/smf/index.php?topic=14088.0


if you examine the details of the GK-3, it becomes apparent MIDI data messages have never existed in ANY 13 pin interface from Roland or Any other manufacturer at anytime.
Essentially the GK-3 is a multichannel analog Buffer/Line driver !

https://www.vguitarforums.com/smf/index.php?topic=7893.msg56178#msg56178

Only Roland Japan Corporate Global site tries to clear up the confusion

Roland COSM Reference Library
https://www.vguitarforums.com/smf/index.php?topic=88.0


http://roland.com/V-Guitar/about.html



Tony Raven