[sdiy] QTC and delurk

[Veronica Merryfield]

Edward

Thank you for your note.

My intention is to build an instrument specially for this project as a test 
bed. There are no frets. For a fretted instrument, there are better ways to 
drive a synth, this is all about fretless.

Plan A has always been to find a way to sense pressure under each string to 
detect position. This would allow a pitch detection and tracking system to 
have a good hint at where it should be looking for the pitch to be. As a 
secondary function, the actual pressure can be used as a modulation control.

Plan B is to make the fingerboard resistive and use the strings as wipers. 
The resistance measurement allows a pitch detection and tracking system to 
have a good hint at where it should be looking for the pitch to be - this 
greatly speeds up and increase accuracy of the detection.

I first thought peizo would work but the pressure frequency relationship 
yeilds results way below what peizo could sense so I started investigating 
plan B. QTC revives plan A if I can my hands on any.

The system still has to rely on pitch detection since a player can bend 
string sideways to change pitch as well as slide up and down the 
fingerboard. It would take a very fine matrix either side of a sensor 
element to capture all this and then there would still be quantization 
issues. Pitch detection's major problem for bass is the long time it takes 
to lock on to pitch. Whilst there are some techniques to speed this up by 
using harmonics and harmonic relationships of string vibrations (harmonic 
shapening), this works best when there is a finite number of possibilities 
to choose from, i.e. fret positions. This systems fails for a fretless 
instruement. However, a system that has some form of hint scheme that can 
steer a pitch detector holds much hope - it's very much like giving a PLL an 
input frequency that is close to where it needs to lock.

If anyone can help on getting QTC, it would be much appreciated.

Veronica

----- Original Message ----- 
From: Edward King
To: Veronica Merryfield
Cc: Synth-DIY
Sent: Sunday, May 13, 2007 7:43 AM
Subject: Re: [sdiy] QTC and delurk


Veronica,

sorry I havent contributed to your problem any since my last post, but I
have a client who have been running me ragged for a few weeks!

The first thing that springs to mind is that there isnt a way of adding qtc
to an instruments fretboard without modifying it in some way (or suffering
string interference). This I guess would mean shaving the fretboard, then
laying the qtc and finally the overlay. gluing veneer directly to the qtc
would be one suggestion (and I think that would be okay), but it leaves the
question of the frets. Given that the qtc material is some 1.something
millimetres thick + the thickness of whatever material your contacts are
attached to, you woul dhave to pick an instrument with adequate fretboard
material. This of course alters the playability of the instrument in
question and you would be right if you baulked at the idea.

If you're as experienced at working with instruments on the construction
level as your previous posts suggest, then rebuiling a neck shouldnt be
beyond your capabilities and this may be whats required given that contacts
would need to be placed underneath the qtc material on every fret (or even
the other way round) or continuously (in the case of a fretless) with the
math taking care of the voltage - pressure - pitch functions. Given that the
qtc material is _almost_ linear in terms of its output, I would suggest a
lookup table with _best fit_ algorithm as Ive gotten very good results with
that for my individual aftertouch, hammer impact velocity and vibrato
systems.

The response times of the qtc material are very good, but of course this
depends on what you're using to monitor it. The data I collected from a
standard 8bit ADC on a PIC microcontroller was perfectly sufficient to
effect a less than 1ms event-process-response mechanism.

Regards

Edward



That is to say that the
----- Original Message ----- 
From: "Veronica Merryfield" <veronica.merryfield at shaw.ca>
To: "synthesizer diy electronics" <synth-diy at dropmix.xs4all.nl>
Sent: Sunday, May 06, 2007 7:20 AM
Subject: Re: [sdiy] QTC and delurk


> >Welcome!
> Thank you
>
>>Are there going to be strings, or will you be pressing directly on the 
>>fingerboard.?
> With strings. I want to be able to play it as a regular bass and inject 
> the
> string pickup signal as sound source into the signal processing chain.
> However, that wouldn't stop one playing the fingerboard :) I figure on
> experimenting with various thicknesses of fingerboard vaneer to make the
> sensors give me a reasonable range of pressure sensing. I'm thinking that
> there might need to be a pressure sensing calibration function too. Hmmm
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy

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