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| -rw-r--r-- | examples/shepard.lua | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/examples/shepard.lua b/examples/shepard.lua new file mode 100644 index 0000000..06958d0 --- /dev/null +++ b/examples/shepard.lua @@ -0,0 +1,52 @@ +-- +-- 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() |