Update a-Amplifier, use Ardour::Amp

This fixes an issue with a-Amp interpolating the parameter in dB,
resulting in a double-exponential fade when the parameter changes.

Now fade is linear in dB, also using Ardour' Amp processor is more
efficient, since interpolation happens in C++.

share/scripts/_amp4.lua

@@ -1,6 +1,6 @@
 ardour {
 	["type"]    = "dsp",
-	name        = "a-Amplifier",
+	name        = "Simple Amp IV",
 	category    = "Amplifier",
 	license     = "MIT",
 	author      = "Ardour Team",
@@ -58,6 +58,7 @@ function dsp_run (ins, outs, n_samples)
 		if siz > n_samples then siz = n_samples end -- process at most "remaining samples"
 		if changed then
 			-- smooth gain changes above 0.02 dB difference
+			-- XXX this interpolates dB, resulting in a double-exponential fade XXX
 			cur_gain = low_pass_filter_param (cur_gain, ctrl[1], 0.02)
 		end
 
@@ -75,45 +76,4 @@ function dsp_run (ins, outs, n_samples)
 		n_samples = n_samples - siz
 		off = off + siz
 	end
-
---[[
-	if changed then
-		self:queue_draw () -- notify display
-	end
---]]
 end
-
--------------------------------------------------------------------------------
---- inline display + text example
-
---[[
-local txt = nil -- cache pango context globally
-
-function render_inline (ctx, w, max_h)
-	local ctrl = CtrlPorts:array () -- get control ports
-
-	if not txt then
-		-- allocate PangoLayout and set font
-		--http://manual.ardour.org/lua-scripting/class_reference/#Cairo:PangoLayout
-		txt = Cairo.PangoLayout (ctx, "Mono 8px")
-	end
-
-	txt:set_text (string.format ("%+.2f dB", ctrl[1]));
-	tw, th = txt:get_pixel_size ()
-
-	local h = th + 4 -- use text-height with 4px padding
-	if (h > max_h) then h = max_h end -- but at most max-height
-
-	-- clear background
-	ctx:rectangle (0, 0, w, h)
-	ctx:set_source_rgba (.2, .2, .2, 1.0)
-	ctx:fill ()
-
-	-- center text
-	ctx:set_source_rgba (.8, .8, .8, 1.0)
-	ctx:move_to (.5 * (w - tw), .5 * (h - th))
-	txt:show_in_cairo_context (ctx)
-
-	return {w, h}
-end
---]]

share/scripts/amp5.lua

@@ -0,0 +1,95 @@
+ardour {
+	["type"]    = "dsp",
+	name        = "a-Amplifier",
+	category    = "Amplifier",
+	license     = "MIT",
+	author      = "Ardour Team",
+	description = [[Versatile +/- 20dB multichannel amplifier]]
+}
+
+function dsp_ioconfig ()
+	return
+	{
+		-- -1, -1 = any number of channels as long as input and output count matches
+		{ audio_in = -1, audio_out = -1},
+	}
+end
+
+
+function dsp_params ()
+	return
+	{
+		{ ["type"] = "input", name = "Gain", min = -20, max = 20, default = 0, unit="dB"},
+	}
+end
+
+local sr = 48000
+local cur_gain = 1
+
+function dsp_init (rate)
+	sr = rate
+end
+
+function dsp_configure (ins, outs)
+	n_out   = outs
+	n_audio = outs:n_audio ()
+	assert (outs:n_midi () == 0)
+end
+
+-- the DSP callback function
+function dsp_runmap (bufs, in_map, out_map, n_samples, offset)
+	-- apply I/O map
+	ARDOUR.DSP.process_map (bufs, n_out, in_map, out_map, n_samples, offset)
+
+	local ctrl = CtrlPorts:array() -- get control port array
+	local target_gain  = ARDOUR.DSP.dB_to_coefficient (ctrl[1]) -- 10 ^ (0.05 * ctrl[1])
+	local current_gain = cur_gain -- start with the same for all channels
+
+	for c = 1, n_audio do
+		local ob = out_map:get (ARDOUR.DataType ("audio"), c - 1); -- get id of mapped output buffer for given cannel
+		if (ob ~= ARDOUR.ChanMapping.Invalid) then
+			cur_gain = ARDOUR.Amp.apply_gain (bufs:get_audio(ob), sr, n_samples, current_gain, target_gain, offset)
+		end
+	end
+
+--[[
+	if current_gain ~= cur_gain then
+		self:queue_draw () -- notify display
+	end
+--]]
+end
+
+-------------------------------------------------------------------------------
+--- inline display + text example
+
+--[[
+local txt = nil -- cache pango context globally
+
+function render_inline (ctx, w, max_h)
+	local ctrl = CtrlPorts:array () -- get control ports
+
+	if not txt then
+		-- allocate PangoLayout and set font
+		--http://manual.ardour.org/lua-scripting/class_reference/#Cairo:PangoLayout
+		txt = Cairo.PangoLayout (ctx, "Mono 8px")
+	end
+
+	txt:set_text (string.format ("%+.2f dB", ctrl[1]));
+	tw, th = txt:get_pixel_size ()
+
+	local h = th + 4 -- use text-height with 4px padding
+	if (h > max_h) then h = max_h end -- but at most max-height
+
+	-- clear background
+	ctx:rectangle (0, 0, w, h)
+	ctx:set_source_rgba (.2, .2, .2, 1.0)
+	ctx:fill ()
+
+	-- center text
+	ctx:set_source_rgba (.8, .8, .8, 1.0)
+	ctx:move_to (.5 * (w - tw), .5 * (h - th))
+	txt:show_in_cairo_context (ctx)
+
+	return {w, h}
+end
+--]]