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ardour {
["type"] = "dsp",
name = "Biquad Filter",
category = "Filter",
license = "MIT",
author = "Robin Gareus",
email = "robin@gareus.org",
site = "http://gareus.org",
description = [[
An Example DSP Plugin for processing audio, to
be used with Ardour's Lua scripting facility.]]
}
function dsp_ioconfig ()
return
{
{ audio_in = -1, audio_out = -1},
}
end
function dsp_params ()
return
{
{ ["type"] = "input", name = "Type", min = 0, max = 4, default = 0, enum = true, scalepoints =
{
["Peaking"] = 0,
["Low Shelf"] = 1,
["High Shelf"] = 2,
["Low Pass"] = 3,
["High Pass"] = 4,
}
},
{ ["type"] = "input", name = "Gain", min = -20, max = 20, default = 0, unit="dB" },
{ ["type"] = "input", name = "Freq", min = 20, max = 20000, default = 1000, unit="Hz", logarithmic = true },
{ ["type"] = "input", name = "Q", min = 0.1, max = 8, default = .707, logarithmic = true },
}
end
-- these globals are *not* shared between DSP and UI
local filt -- the filter instance
local cur = {0, 0, 0, 0} -- current settings
function dsp_init (rate)
self:shmem ():allocate (1) -- shared mem to tell UI about samplerate
local cfg = self:shmem ():to_int (0):array ()
cfg[1] = rate
filt = ARDOUR.DSP.Biquad (rate) -- initialize filter
end
-- apply parameters, re-compute filter coefficients if needed
function apply_params (ctrl)
if ctrl[1] == cur[1] and ctrl[2] == cur[2] and ctrl[3] == cur[3] and ctrl[4] == cur[4] then
return false
end
local ft
if ctrl[1] == 1 then
ft = ARDOUR.DSP.BiQuadType.LowShelf
elseif ctrl[1] == 2 then
ft = ARDOUR.DSP.BiQuadType.HighShelf
elseif ctrl[1] == 3 then
ft = ARDOUR.DSP.BiQuadType.LowPass
elseif ctrl[1] == 4 then
ft = ARDOUR.DSP.BiQuadType.HighPass
else
ft = ARDOUR.DSP.BiQuadType.Peaking
end
-- TODO low-pass filter ctrl values, smooth transition
filt:compute (ft, ctrl[3], ctrl[4], ctrl[2])
cur[1] = ctrl[1]
cur[2] = ctrl[2]
cur[3] = ctrl[3]
cur[4] = ctrl[4]
return true
end
-- the actual DSP callback
function dsp_run (ins, outs, n_samples)
if apply_params (CtrlPorts:array ()) then
self:queue_draw ()
end
for c = 1,#ins do
if ins[c]:sameinstance (outs[c]) then
filt:run (ins[c], n_samples) -- in-place
else
ARDOUR.DSP.copy_vector (outs[c], ins[c], n_samples)
filt:run (outs[c], n_samples)
end
end
end
-------------------------------------------------------------------------------
--- inline display
function round (n)
return math.floor (n + .5)
end
function freq_at_x (x, w)
return 20 * 1000 ^ (x / w)
end
function x_at_freq (f, w)
return w * math.log (f / 20.0) / math.log (1000.0)
end
function db_to_y (db, h)
if db < -20 then db = -20 end
if db > 20 then db = 20 end
return -.5 + 0.5 * h * (1 - db / 20)
end
function grid_db (ctx, w, h, db)
local y = -.5 + round (db_to_y (db, h))
ctx:move_to (0, y)
ctx:line_to (w, y)
ctx:stroke ()
end
function grid_freq (ctx, w, h, f)
local x = -.5 + round (x_at_freq (f, w))
ctx:move_to (x, 0)
ctx:line_to (x, h)
ctx:stroke ()
end
function render_inline (ctx, w, max_h)
if not filt then
-- instantiate filter (to calculate the transfer function)
local shmem = self:shmem () -- get shared memory region
local cfg = shmem:to_int (0):array () -- "cast" into lua-table
filt = ARDOUR.DSP.Biquad (cfg[1])
end
apply_params (CtrlPorts:array ())
-- calc height of inline display
local h = math.ceil (w * 10 / 16) -- 16:10 aspect
h = 2 * round (h / 2) -- even number of vertical px
if (h > max_h) then
h = max_h
end
-- clear background
ctx:rectangle (0, 0, w, h)
ctx:set_source_rgba (.2, .2, .2, 1.0)
ctx:fill ()
ctx:set_line_width (1.0)
-- draw grid
local dash3 = C.DoubleVector ()
dash3:add ({1, 3})
ctx:set_dash (dash3, 2)
ctx:set_source_rgba (.5, .5, .5, .5)
grid_db (ctx, w, h, 0)
grid_db (ctx, w, h, 6)
grid_db (ctx, w, h, 12)
grid_db (ctx, w, h, 18)
grid_db (ctx, w, h, -6)
grid_db (ctx, w, h, -12)
grid_db (ctx, w, h, -18)
grid_freq (ctx, w, h, 100)
grid_freq (ctx, w, h, 1000)
grid_freq (ctx, w, h, 10000)
ctx:unset_dash ()
-- draw transfer function
ctx:set_source_rgba (.8, .8, .8, 1.0)
ctx:move_to (-.5, db_to_y (filt:dB_at_freq (freq_at_x (0, w)), h))
for x = 1,w do
local db = filt:dB_at_freq (freq_at_x (x, w))
ctx:line_to (-.5 + x, db_to_y (db, h))
end
ctx:stroke_preserve ()
-- fill area to zero under the curve
ctx:line_to (w, -.5 + h * .5)
ctx:line_to (0, -.5 + h * .5)
ctx:close_path ()
ctx:set_source_rgba (.5, .5, .5, .5)
ctx:fill ()
return {w, h}
end
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