Re: Fretless MIDI guitar

[Richard Zvonar <zvonar@zvonar.com>]

At 8:33 AM -0800 1/2/03, S V G wrote:
>My understanding of the Godin/RMC system is that it outputs the 
>acoustic signal (pitch information) for each string on separate 
>channels.

RMC also makes the Freakout Box, which provides individual audio 
outputs per string. This presents interesting possibilities for 
surround sound and for string-specific effects processing.

>From there it is up to the pitch to MIDI converter to unravel all 
>this information...if you play a note within 50 cents (half a 
>semitone)
>either side of middle C with a fretless guitar, the pitch to MIDI 
>device will output the note "C" plus the appropriate pitch bend 
>information (or not).  Another note played within 50 cents either 
>side of C# will trigger a new note as "C#".  The only time this 
>doesn't hold true is when you pluck a note and then slide your 
>finger up or down the string.  The note has already been
>activated and chosen and then the pitch bend information is sent to 
>modify that note up or down an octave or more.

This system has both advantages and disadvantages. It assumes that 
pitch bends will always start within a semitone of the nominal pitch, 
but it's quite common for some players to bend down from a whole tone 
or a minor third above.

The system I mention as being available on the Peavey Cyberbass (each 
string outputs a single MIDI note plus pitch bend within a two octave 
range) has some interesting possibilities for fretless and even 
fretted MIDI guitars. For instance, it allows playing with flexible 
intonation. Microtonal players (whose pitch discrimination can be 
uncanny) would be able to play guitar synth in Just  or other 
intonations without the synth having microtonal features. Even though 
many synths have tuning capabilities, it requires switching presets 
in order to change from one to another. With a MIDI pitch bend based 
system the intonation would be left entirely to the player.

There are certain technical issues related to pitch bend resolution. 
Unfortunately most MIDI equipment seems to be designed with 7-bit 
pitch bend and this permits only 128 discrete values. This means that 
bends are limited to 63 or 64 steps up OR down. With a semitone bend 
the individual steps are about 1.5 cents; a while tone is about 3.1 
cents. Both are OK, but if you stretch 128 values over a two octave 
range you get pitch increments of nearly 19 cents! The technical 
solution to this is to use the full two-byte, 14-bit resolution 
allowed by MIDI, resulting in 16,384 steps and pitch resolution of 
about 0.15 cents. I don't think there are many sound modules that can 
match that. The Cyberbass Voice Module and the Oberheim Matrix synths 
can handle it.


>C3

BTW - Middle C is "C4" no matter what Yamaha says.

>This is a long winded way of saying that the Godin fretless synth 
>access guitar will probably work well with either the Roland GR 
>series or the Axon/Yamaha guitar synths.

Not long-winded. Necessarily clear and detailed!

>I can personally vouch for the Godin/RMC combination, the sound of 
>my nylon Multiac is extremely satisfying to my ears as a classical 
>guitarist.

Any comments on the difference between Multiac and ACS-SA?
-- 

______________________________________________________________
Richard Zvonar, PhD
(818) 788-2202
http://www.zvonar.com
http://RZCybernetics.com