ar.lua

--- ar - ar envelope generator
--    https://github.com/pchuck/monome-crow
--
-- in1: trigger
-- in2: n/a
-- out1: ar envelope 
-- out2: "
-- out3: "
-- out4: "

-- constants
local V_THRESH = 1.0 -- trigger threshold in volts
local V_HYST = 0.1 -- hysteresis voltage
local TRIG = 'rising' -- trigger condition
local IN_GATE = 1 -- gate input
local IN_CV = 2 -- cv input (not used in this version)
local OUTS = { 1, 2, 3, 4 } -- outputs - logical ids of the lfo outputs
local MAX_V = 10 -- maximum envelope output (v)
local MAX_T = 10 -- maximum phase length (s)

-- public (values that can be changed remotely or at run-time, eg via druid:)
--   > public.a = 0.1
--
--                 __ max_level
--    / \    
--   /   \               __ min_level
--   
--   a | r 
--
public.add('a',        0.01, { 0, MAX_T }) -- attack time (s)
public.add('r',         0.5, { 0, MAX_T }) -- release time (s)
public.add('max_level',   7, { 0, MAX_V }) -- max level (v)
public.add('min_level',   0, { 0, MAX_V }) -- min level (v)
public.add('shape', 'log', -- envelope shape
           {'linear', 'sine', 'logarithmic', 'exponential',
            'over', 'under', 'rebound'}) 

-- initialization
function init()
   -- trigger on first input
   input[IN_GATE].mode('change', V_THRESH, V_HYST, TRIG)
   input[IN_GATE].change = function() change() end -- the call-back function
   print('ar initialized')
end

-- improvement over the asllib ar() envelope function
--   allows specification of min level
function ar2(a, r, max_level, min_level, shape)
   -- print(a, r, max_level, min_level, shape)
   return{ to(max_level, a, shape), to(min_level, r, shape) }
end

-- trigger call-back
function change()
   local cv = input[IN_CV].volts
   for _, v in pairs(OUTS) do -- output same env on all outputs
      output[v].action = { ar2(public.a,
                               public.r,
                               public.max_level,
                               public.min_level,
                               public.shape) }
      output[v]() -- (re)trigger the envelope
   end
end