I've been "building" an "instrument". Thanks to some samples from Ivan Reese.

To recreate the above you need:

1. To install LÖVE for your platform (really just Android or iOS since we're talking multitouch in this post.)
2. Download a special build of MiniIDE containing Ivan's samples.
3. Paste in the following 70-line script and hit 'Run':

   g = love.graphics
   draw, line, circ, pt, color = g.draw, g.line, g.circle, g.points, g.setColor
   abs,min,max = math.abs, math.min, math.max
   audio = love.audio.newSource
   if od == nil then
       od,ou,omp,omr,okp,okr = love.draw, love.update, love.mousepressed,
   love.mousereleased, love.keypressed, love.keyreleased
   end
   W,H = g.getDimensions()
   -- visuals
   cs, N = {}, 100
   function sq(x) return x*x end
   function dist2(x1,y1, x2,y2)
     return sq(x2-x1) + sq(y2-y1)
   end
   
   -- audio
   ts = {}
   
   function love.draw() -- od()
     for _,c in pairs(cs) do
       circ(c[1],c[2])
     end
   end
   
   function circ(cx,cy)
     for x=cx-N,cx+N do
       for y=cy-N,cy+N do
         local dist = dist2(cx,cy, x,y)
         if dist < N*N then
           color(abs(x-cx)/N, abs(y-cy)/N, 0.5) --, dist/N/N)
           pt(x,y) end end end
   end
   
   function love.update(dt) ou(dt)
     local touches = love.touch.getTouches()
     for _,id in ipairs(touches) do
       if cs[id] then
       cs[id][1], cs[id][2] = love.touch.getPosition(id)
       ts[id]:setPitch(pitch(cs[id][2]))
       end
     end
   end
   
   function pitch(y)
     if y <= H/2 then
       return 2 - y*2/H  -- vary pitch from 2 to 1
     else
       return 1.5 - y/H  -- vary pitch from 1 to 0.5
     end
   end
   
   function love.keypressed(key, ...) okp(key, ...)
     escape()
   end
   
   function love.touchpressed(id, x,y, ...)
     cs[id] = {x,y}
     ts[id] = audio('ivanish/MaternalBowedGuitar.mp3', 'static')
     ts[id]:setLooping(true)
     ts[id]:play()
   end
   
   function love.touchreleased(id, ...)
     cs[id] = nil
     if ts[id] then ts[id]:stop() end
     ts[id] = nil
   end
   
   function escape()
     error('StopScript')
   end
   

One of those 70 lines contains 'ivanish', and I've been playing with that line by varying the sample. (Unfortunately there isn't a way to browse the list, so you have to look inside the love/zip file.)

This post is part of my Freewheeling Apps Devlog.

Comments gratefully appreciated. Please send them to me by any method of your choice and I'll include them here.