add a lua high/low pass filter with configurable slope

1 files changed, 273 insertions, 0 deletions

diff --git a/scripts/hplp.lua b/scripts/hplp.lua
new file mode 100644
index 0000000000..3b6a34c0fd
--- /dev/null
+++ b/scripts/hplp.lua
@@ -0,0 +1,273 @@
+ardour {
+	["type"]    = "dsp",
+	name        = "High/Low Pass Filter",
+	category    = "Filter",
+	license     = "MIT",
+	author      = "Robin Gareus",
+	email       = "robin@gareus.org",
+	site        = "http://gareus.org",
+	description = [[Example Ardour Lua DSP Plugin]]
+}
+
+function dsp_ioconfig ()
+	return
+	{
+		-- allow any number of I/O as long as port-count matches
+		{ audio_in = -1, audio_out = -1},
+	}
+end
+
+
+function dsp_params ()
+	return
+	{
+		{ ["type"] = "input", name = "Type", min = 0, max = 1, default = 0, enum = true, scalepoints =
+			{
+				["High Pass"]  = 0,
+				["Low Pass"]   = 1,
+			}
+		},
+		{ ["type"] = "input", name = "Steepness", min = 1, max = 4, default = 1, enum = true, scalepoints =
+			{
+				["12dB/oct"] = 1,
+				["24dB/oct"] = 2,
+				["36dB/oct"] = 3,
+				["48dB/oct"] = 4,
+			}
+		},
+		{ ["type"] = "input", name = "Cut off frequency", min =   5, max = 20000, default = 1000, unit="Hz", logarithmic = true },
+		{ ["type"] = "input", name = "Resonance",         min = 0.1, max = 8,     default = .707, logarithmic = true },
+	}
+end
+
+-- translate type parameter to DSP enum
+-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR.DSP.Biquad.Type
+function map_type (t)
+	if     t == 1 then
+		return ARDOUR.DSP.BiquadType.LowPass
+	else
+		return ARDOUR.DSP.BiquadType.HighPass
+	end
+end
+
+-- these globals are *not* shared between DSP and UI
+local filters = {}  -- the biquad filter instances (DSP)
+local filt -- the biquad filter instance (GUI, response)
+local cur = {0, 0, 0, 0} -- current parameters
+local lpf = 0.03 -- parameter low-pass filter time-constant
+
+function dsp_init (rate)
+	self:shmem ():allocate (1) -- shared mem to tell the GUI the samplerate
+	local cfg = self:shmem ():to_int (0):array ()
+	cfg[1] = rate
+	-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP:Biquad
+	for k = 1,4 do
+		filters[k] = ARDOUR.DSP.Biquad (rate) -- initialize filters
+	end
+	lpf = 13000 / rate -- interpolation time constant
+end
+
+-- helper functions for parameter interpolation
+function param_changed (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
+	return true
+end
+
+function low_pass_filter_param (old, new, limit)
+	if math.abs (old - new) < limit  then
+		return new
+	else
+		return old + lpf * (new - old)
+	end
+end
+
+-- apply parameters, re-compute filter coefficients if needed
+function apply_params (ctrl)
+	if not param_changed (ctrl) then
+		return
+	end
+
+	if cur[1] ~= ctrl[1] or cur[2] ~= ctrl[2] then
+		-- reset filter state when type or order changes
+		for k = 1,4 do
+			filters[k]:reset ()
+		end
+		for k = 1,4 do cur[k] = ctrl[k] end
+	else
+		-- low-pass filter ctrl parameter values, smooth transition
+		cur[3] = low_pass_filter_param (cur[3], ctrl[3], 1.0) -- freq/Hz
+		cur[4] = low_pass_filter_param (cur[4], ctrl[4], 0.01) -- quality
+	end
+
+	if cur[2] < 1 then cur[2] = 1 end
+	if cur[2] > 4 then cur[2] = 4 end
+
+	for k = 1,4 do
+		filters[k]:compute (map_type (cur[1]), cur[3], cur[4], 0)
+	end
+end
+
+
+-- the actual DSP callback
+function dsp_run (ins, outs, n_samples)
+	local changed = false
+	local siz = n_samples
+	local off = 0
+
+	-- if a parameter was changed, process at most 64 samples at a time
+	-- and interpolate parameters until the current settings match
+	-- the target values
+	if param_changed (CtrlPorts:array ()) then
+		changed = true
+		siz = 64
+	end
+
+	local o = cur[2]
+
+	while n_samples > 0 do
+		if changed then apply_params (CtrlPorts:array ()) end
+		if siz > n_samples then siz = n_samples end
+
+		-- process all channels
+		for c = 1,#ins do
+			-- check if output and input buffers for this channel are identical
+			-- http://manual.ardour.org/lua-scripting/class_reference/#C:FloatArray
+			if ins[c]:sameinstance (outs[c]) then
+				for k = 1,o do
+					filters[k]:run (ins[c]:offset (off), siz) -- in-place processing
+				end
+			else
+				-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP
+				ARDOUR.DSP.copy_vector (outs[c]:offset (off), ins[c]:offset (off), siz)
+				for k = 1,o do
+					filters[o]:run (outs[c]:offset (off), siz)
+				end
+			end
+		end
+
+		n_samples = n_samples - siz
+		off = off + siz
+	end
+
+	if changed then
+		-- notify display
+		self:queue_draw ()
+	end
+end
+
+
+-------------------------------------------------------------------------------
+--- inline display
+
+function round (n)
+	return math.floor (n + .5)
+end
+
+function freq_at_x (x, w)
+	-- x-axis pixel for given freq, power-scale
+	return 20 * 1000 ^ (x / w)
+end
+
+function x_at_freq (f, w)
+	-- frequency at given x-axis pixel
+	return w * math.log (f / 20.0) / math.log (1000.0)
+end
+
+function db_to_y (db, h)
+	-- y-axis gain mapping
+	if db < -48 then db = -48 end
+	if db >  12 then db =  12 end
+	return -.5 + round (0.2 * h) - h * db / 60
+end
+
+function grid_db (ctx, w, h, db)
+	-- draw horizontal grid line
+	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)
+	-- draw vertical grid line
+	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
+		-- the GUI is separate from the DSP, but the GUI needs to know
+		-- the sample-rate that the DSP is using.
+		local shmem = self:shmem () -- get shared memory region
+		local cfg = shmem:to_int (0):array () -- "cast" into lua-table
+		-- instantiate filter (to calculate the transfer function's response)
+		filt = ARDOUR.DSP.Biquad (cfg[1])
+	end
+
+	-- set filter coefficients if they have changed
+	if param_changed (CtrlPorts:array ()) then
+		local ctrl = CtrlPorts:array ()
+		for k = 1,4 do cur[k] = ctrl[k] end
+		if cur[2] < 1 then cur[2] = 1 end
+		if cur[2] > 4 then cur[2] = 4 end
+		filt:compute (map_type (cur[1]), cur[3], cur[4], 0)
+	end
+
+	-- calc height of inline display
+	local h = math.ceil (w * 10 / 16) -- use 16:10 aspect
+	if (h > max_h) then h = max_h end -- but at most max-height
+
+	-- ctx is a http://cairographics.org/ context
+	-- http://manual.ardour.org/lua-scripting/class_reference/#Cairo:Context
+
+	-- clear background
+	ctx:rectangle (0, 0, w, h)
+	ctx:set_source_rgba (.2, .2, .2, 1.0)
+	ctx:fill ()
+
+	-- set line width: 1px
+	-- Note: a cairo pixel at [1,1]  spans [0.5->1.5 , 0.5->1.5]
+	-- hence the offset -0.5 in various move_to(), line_to() calls
+	ctx:set_line_width (1.0)
+
+	-- draw grid
+	local dash3 = C.DoubleVector ()
+	local dash2 = C.DoubleVector ()
+	dash2:add ({1, 2})
+	dash3:add ({1, 3})
+	ctx:set_dash (dash2, 2) -- dotted line
+	ctx:set_source_rgba (.5, .5, .5, .8)
+	grid_db (ctx, w, h, 0)
+	ctx:set_dash (dash3, 2) -- dotted line
+	ctx:set_source_rgba (.5, .5, .5, .5)
+	grid_db (ctx, w, h, -12)
+	grid_db (ctx, w, h, -24)
+	grid_db (ctx, w, h, -36)
+	grid_freq (ctx, w, h, 100)
+	grid_freq (ctx, w, h, 1000)
+	grid_freq (ctx, w, h, 10000)
+	ctx:unset_dash ()
+
+	local o = cur[2]
+	-- draw transfer function line
+	ctx:set_source_rgba (.8, .8, .8, 1.0)
+	ctx:move_to (-.5, db_to_y (o * filt:dB_at_freq (freq_at_x (0, w)), h))
+	for x = 1,w do
+		local db = o * 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 + round (db_to_y (0, h)))
+	ctx:line_to (0, -.5 + round (db_to_y (0, h)))
+	ctx:close_path ()
+	ctx:set_source_rgba (.5, .5, .5, .5)
+	ctx:fill ()
+
+	return {w, h}
+end