complete lua DSP filter with parameter interpolation & comments
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163
scripts/filt.lua
163
scripts/filt.lua
@ -6,14 +6,13 @@ ardour {
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author = "Robin Gareus",
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email = "robin@gareus.org",
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site = "http://gareus.org",
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description = [[
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An Example DSP Plugin for processing audio, to
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be used with Ardour's Lua scripting facility.]]
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description = [[Example Ardour Lua DSP Plugin]]
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}
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function dsp_ioconfig ()
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return
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{
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-- allow any number of I/O as long as port-count matches
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{ audio_in = -1, audio_out = -1},
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}
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end
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@ -37,59 +36,111 @@ function dsp_params ()
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}
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end
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-- these globals are *not* shared between DSP and UI
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local filt -- the filter instance
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local cur = {0, 0, 0, 0} -- current settings
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function dsp_init (rate)
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self:shmem ():allocate (1) -- shared mem to tell UI about samplerate
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local cfg = self:shmem ():to_int (0):array ()
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cfg[1] = rate
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filt = ARDOUR.DSP.Biquad (rate) -- initialize filter
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-- translate type parameter to DSP enum
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-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR.DSP.Biquad.Type
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function map_type (t)
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if t == 1 then
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return ARDOUR.DSP.BiquadType.LowShelf
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elseif t == 2 then
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return ARDOUR.DSP.BiquadType.HighShelf
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elseif t == 3 then
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return ARDOUR.DSP.BiquadType.LowPass
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elseif t == 4 then
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return ARDOUR.DSP.BiquadType.HighPass
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else
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return ARDOUR.DSP.BiquadType.Peaking
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end
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end
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-- these globals are *not* shared between DSP and UI
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local filt -- the biquad filter instance
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local cur = {0, 0, 0, 0} -- current parameters
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local lpf = 0.03 -- parameter low-pass filter time-constant
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-- apply parameters, re-compute filter coefficients if needed
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function apply_params (ctrl)
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function dsp_init (rate)
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self:shmem ():allocate (1) -- shared mem to tell the GUI the samplerate
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local cfg = self:shmem ():to_int (0):array ()
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cfg[1] = rate
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-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP:Biquad
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filt = ARDOUR.DSP.Biquad (rate) -- initialize filter
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lpf = 13000 / rate -- interpolation time constant
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end
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-- helper functions for parameter interpolation
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function param_changed (ctrl)
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if ctrl[1] == cur[1] and ctrl[2] == cur[2] and ctrl[3] == cur[3] and ctrl[4] == cur[4] then
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return false
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end
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return true
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end
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local ft
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if ctrl[1] == 1 then
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ft = ARDOUR.DSP.BiQuadType.LowShelf
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elseif ctrl[1] == 2 then
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ft = ARDOUR.DSP.BiQuadType.HighShelf
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elseif ctrl[1] == 3 then
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ft = ARDOUR.DSP.BiQuadType.LowPass
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elseif ctrl[1] == 4 then
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ft = ARDOUR.DSP.BiQuadType.HighPass
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function low_pass_filter_param (old, new, limit)
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if math.abs (old - new) < limit then
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return new
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else
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ft = ARDOUR.DSP.BiQuadType.Peaking
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return old + lpf * (new - old)
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end
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end
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-- apply parameters, re-compute filter coefficients if needed
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function apply_params (ctrl)
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if not param_changed (ctrl) then
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return
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end
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-- TODO low-pass filter ctrl values, smooth transition
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filt:compute (ft, ctrl[3], ctrl[4], ctrl[2])
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cur[1] = ctrl[1]
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cur[2] = ctrl[2]
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cur[3] = ctrl[3]
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cur[4] = ctrl[4]
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return true
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if cur[1] ~= ctrl[1] then
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-- reset filter state when type changes
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filt:reset ()
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for k = 1,4 do cur[k] = ctrl[k] end
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else
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-- low-pass filter ctrl parameter values, smooth transition
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cur[2] = low_pass_filter_param (cur[2], ctrl[2], 0.1) -- gain/dB
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cur[3] = low_pass_filter_param (cur[3], ctrl[3], 1.0) -- freq/Hz
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cur[4] = low_pass_filter_param (cur[4], ctrl[4], 0.01) -- quality
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end
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filt:compute (map_type (cur[1]), cur[3], cur[4], cur[2])
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end
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-- the actual DSP callback
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function dsp_run (ins, outs, n_samples)
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if apply_params (CtrlPorts:array ()) then
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self:queue_draw ()
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local changed = false
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local siz = n_samples
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local off = 0
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-- if a parameter was changed, process at most 64 samples at a time
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-- and interpolate parameters until the current settings match
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-- the target values
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if param_changed (CtrlPorts:array ()) then
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changed = true
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siz = 64
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end
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for c = 1,#ins do
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if ins[c]:sameinstance (outs[c]) then
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filt:run (ins[c], n_samples) -- in-place
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else
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ARDOUR.DSP.copy_vector (outs[c], ins[c], n_samples)
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filt:run (outs[c], n_samples)
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while n_samples > 0 do
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if changed then apply_params (CtrlPorts:array ()) end
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if siz > n_samples then siz = n_samples end
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-- process all channels
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for c = 1,#ins do
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-- check if output and input buffers for this channel are identical
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-- http://manual.ardour.org/lua-scripting/class_reference/#C:FloatArray
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if ins[c]:sameinstance (outs[c]) then
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filt:run (ins[c]:offset (off), siz) -- in-place processing
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else
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-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP
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ARDOUR.DSP.copy_vector (outs[c]:offset (off), ins[c]:offset (off), siz)
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filt:run (outs[c]:offset (off), siz)
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end
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end
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n_samples = n_samples - siz
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off = off + siz
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end
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if changed then
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-- notify display
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self:queue_draw ()
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end
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end
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@ -102,20 +153,24 @@ function round (n)
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end
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function freq_at_x (x, w)
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-- x-axis pixel for given freq, power-scale
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return 20 * 1000 ^ (x / w)
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end
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function x_at_freq (f, w)
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-- frequency at given x-axis pixel
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return w * math.log (f / 20.0) / math.log (1000.0)
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end
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function db_to_y (db, h)
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-- y-axis gain mapping
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if db < -20 then db = -20 end
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if db > 20 then db = 20 end
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return -.5 + 0.5 * h * (1 - db / 20)
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end
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function grid_db (ctx, w, h, db)
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-- draw horizontal grid line
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local y = -.5 + round (db_to_y (db, h))
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ctx:move_to (0, y)
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ctx:line_to (w, y)
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@ -123,6 +178,7 @@ function grid_db (ctx, w, h, db)
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end
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function grid_freq (ctx, w, h, f)
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-- draw vertical grid line
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local x = -.5 + round (x_at_freq (f, w))
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ctx:move_to (x, 0)
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ctx:line_to (x, h)
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@ -131,32 +187,43 @@ end
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function render_inline (ctx, w, max_h)
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if not filt then
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-- instantiate filter (to calculate the transfer function)
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-- the GUI is separate from the DSP, but the GUI needs to know
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-- the sample-rate that the DSP is using.
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local shmem = self:shmem () -- get shared memory region
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local cfg = shmem:to_int (0):array () -- "cast" into lua-table
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-- instantiate filter (to calculate the transfer function's response)
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filt = ARDOUR.DSP.Biquad (cfg[1])
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end
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apply_params (CtrlPorts:array ())
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-- set filter coefficients if they have changed
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if param_changed (CtrlPorts:array ()) then
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local ctrl = CtrlPorts:array ()
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for k = 1,4 do cur[k] = ctrl[k] end
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filt:compute (map_type (cur[1]), cur[3], cur[4], cur[2])
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end
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-- calc height of inline display
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local h = math.ceil (w * 10 / 16) -- 16:10 aspect
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h = 2 * round (h / 2) -- even number of vertical px
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if (h > max_h) then
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h = max_h
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end
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local h = math.ceil (w * 10 / 16) -- use 16:10 aspect
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h = 2 * round (h / 2) -- with an even number of vertical pixels
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if (h > max_h) then h = max_h end -- but at most max-height
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-- ctx is a http://cairographics.org/ context
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-- http://manual.ardour.org/lua-scripting/class_reference/#Cairo:Context
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-- clear background
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ctx:rectangle (0, 0, w, h)
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ctx:set_source_rgba (.2, .2, .2, 1.0)
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ctx:fill ()
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-- set line width: 1px
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-- Note: a cairo pixel at [1,1] spans [0.5->1.5 , 0.5->1.5]
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-- hence the offset -0.5 in various move_to(), line_to() calls
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ctx:set_line_width (1.0)
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-- draw grid
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local dash3 = C.DoubleVector ()
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dash3:add ({1, 3})
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ctx:set_dash (dash3, 2)
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ctx:set_dash (dash3, 2) -- dotted line
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ctx:set_source_rgba (.5, .5, .5, .5)
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grid_db (ctx, w, h, 0)
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grid_db (ctx, w, h, 6)
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@ -170,7 +237,7 @@ function render_inline (ctx, w, max_h)
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grid_freq (ctx, w, h, 10000)
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ctx:unset_dash ()
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-- draw transfer function
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-- draw transfer function line
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ctx:set_source_rgba (.8, .8, .8, 1.0)
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ctx:move_to (-.5, db_to_y (filt:dB_at_freq (freq_at_x (0, w)), h))
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for x = 1,w do
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