added the Sheppard-Rice-Glissando example: this can also be run in ba…

…tch mode

examples/shepard.lua

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+--
+-- adapted from ChucK's shepard.ck (Ge Wang, 2016)
+--
+local min, max, exp = math.min, math.max, math.exp
+
+local function dbtorms(f)
+	f = min(max(f, 0), 485)
+	return exp((2.302585092994 * 0.05) * (f-100))
+end
+
+local SQRT_PI2 = math.sqrt(2*math.pi)
+local function gauss(x, mu, sd)
+	return (1.0 / (sd*SQRT_PI2)) * exp(-(x-mu)^2 / (2*sd^2))
+end
+
+-- built-in mtof() caches all 128 MIDI notes
+local function mtof_raw(note)
+	return 440 * 2^((note - 69)/12)
+end
+
+-- mean for normal intensity curve
+local MU = 66
+-- standard deviation for normal intensity curve
+local SIGMA = 42
+-- normalize to 1.0 at x==MU
+local SCALE = 1 / gauss(MU, MU, SIGMA)
+-- increment per sample (use negative for descending)
+--local INC = tostream(.004 / msec(1))
+local INC = EvdevStream("TrackPoint"):evrel('REL_X'):scale(-0.008, 0.008):div(msec(1)):cache()
+
+-- starting pitches (in MIDI note numbers, octaves apart)
+local pitches = {12, 24, 36, 48, 60, 72, 84, 96, 108}
+
+local function mtoamp(note)
+	-- compute loundess for each tone
+	local intensity = gauss(note, MU, SIGMA)*SCALE
+	-- map intensity to amplitude
+	return dbtorms(intensity*96)
+end
+
+tostream(pitches):map(function(m)
+	local tone = INC:scan(function(last, inc)
+		local next = (last or m)+inc
+		if next > 120 then
+			next = next - 108
+		elseif next < 12 then
+			next = next + 108
+		end
+		return next
+	end):cache()
+	return tone:map(mtof_raw):TriOsc() * tone:map(mtoamp)
+end):fold(function(a, b) return a+b end):ravel():gain(1/#pitches):play()