electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
 Forum index » DIY Hardware and Software » Musical Interfaces
Expressiv MIDI guitar implementation
Post new topic   Reply to topic
Page 1 of 1 [1 Post]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
sile



Joined: Nov 06, 2017
Posts: 1
Location: shenzhen

PostPosted: Mon Nov 06, 2017 2:31 am    Post subject: Expressiv MIDI guitar implementation Reply with quote  Mark this post and the followings unread

Confusing, so I express some simplify views for Rorguitars. Have a little bit nervous. Confused
Rorguitars claim to have the best MIDI* guitar system on the market. Their website says:

Our guitars do not have MIDI pickups. There is NO pitch detection to send the MIDI signals. Our instruments use an electronic system that senses the frets you press on the fretboard and sends the corresponding notes. [Thanks to Steve G for pointing this out.]
It's not possible to get polyphonic guitar to MIDI conversion based on electrical string/fret contact scanning alone (segmented frets pose wear problems, and it doesn't look like they use them in their product), so some additional sensing must be involved. Multipress keyboards are possible but they can use diodes to prevent crossfeed between rows and columns. This isn't possible on the point of contact between string and fret.

Apparently developed at University of Limerick, Ireland, there is no further info on the web. Probably they don't want to disclose it.

What techniques could be employed to determine the highest fret pressed on each string in such an instrument while handling the short circuits produced by multiple string presses on multiple frets? (Each string press contacts the fret above and below the point of pressure.)

To illustrate:

Posted Image, might have been reduced in size. Click Image to view fullscreen.
Frets and strings form a matrix which can be scanned.

Single notes and notes apart more than two frets pose no problem, but ambiguity arises with close spaced chords, here a simple doublestop.

Both the G and D string read frets 2,3 and 4, as the conducting path in blue crosses strings.

Determining the shortest path (in green) provides the additional information required to discern chord shapes.

Out of the possibilities

Capacitance
Resistance
Reflectometry
for string sensing, lets pick the last option - not least for the purposes of being specific. Also the first two might be influenced by hand contact.

It is not necessary to detect exact lengths, being able to compare whether one fret is closer than the other is sufficient.

So the question is whether it's feasible, given the required rise times, to implement this in a suitable form factor.

Edit:

I found an interesting patent from 1984 (US4630520) by Turtle Beach cofounder Carmine Bonanno.

Wonder why it never took off.

It's the combination approach I had in mind, only with resistance sensing, as suggested by Transistor.

Frets and strings are scanned separately by multiplexers. As reliability issue he stressed the fret/string contact resistance, requiring low current, therefore high input impedance.

I wonder however if an (initial) sufficiently high wetting current (snubber capacitor?) might help alleviate noisy junctions.

MIDI (/ˈmɪdi/; short for Musical Instrument Digital Interface) is a technical standard that describes a protocol, digital interface and connectors and allows a wide variety of electronic musical instruments, computers and other related devices to connect and communicate with one another.
MIDI carries event messages that specify notation, pitch and velocity, control signals for parameters such as volume, vibrato, audio panning, cues, and clock signals that set and synchronize tempo between multiple devices.

Generating MIDI signals from non-keyboard instruments such as, in this case, a guitar poses some interesting electronic design challenges. While keyboard instruments are relatively straight-forward to digitise string and wind instruments have many more nuances that are difficult to detect and measure and, therefore, difficult to convert to MIDI.
Thanks

[Blue Hell: removed the diode spam link, the rest of the text seemed more or less interesting though]
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic
Page 1 of 1 [1 Post]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software » Musical Interfaces
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use