Prefer using C++ DSP for noise generation in scripts

This significantly reduces the DSP load of the noise
generator (avg. process time is reduced by a factor of 8 or more).

share/scripts/_noisegen.lua

@@ -0,0 +1,111 @@
+ardour {
+	["type"]    = "dsp",
+	name        = "NoiseGen",
+	category    = "Instrument",
+	license     = "MIT",
+	author      = "Ardour Team",
+	description = [[Noise Generator (v-1.02)]]
+}
+
+function dsp_params ()
+	return
+	{
+		{ ["type"] = "input", name = "White/Pink", min = 0, max = 1, default = 0, toggled = true },
+		{ ["type"] = "input", name = "Gain", min = -60, max = 0, default = -18, unit="dB" },
+	}
+end
+
+function dsp_ioconfig ()
+	return { [1] = { audio_in = -1, audio_out = -1}, }
+end
+
+local sr = 0
+
+function dsp_init (rate)
+	sr = rate
+end
+
+local ao = 0
+local draw = 0
+
+function dsp_run (ins, outs, n_samples)
+
+	local a = {} -- init array
+	local ctrl = CtrlPorts:array ()
+	local noise = ctrl[1] or 0
+	local amplitude =  ARDOUR.DSP.dB_to_coefficient (ctrl[2]) or ARDOUR.DSP.dB_to_coefficient (-18)
+
+	local b0 = 0.0
+	local b1 = 0.0
+	local b2 = 0.0
+	local b3 = 0.0
+	local b4 = 0.0
+	local b5 = 0.0
+	local b6 = 0.0
+
+	--Pink noise generation courtesy of Paul Kellet's refined method
+	--http://www.musicdsp.org/files/pink.txt
+	--If 'white' consists of uniform random numbers,
+	--the pink noise will have an almost gaussian distribution.
+	for s = 1, n_samples do
+		if noise == 0 then
+			a[s] = amplitude * 2 * (math.random() - 0.5)
+		end
+		if noise == 1 then
+			white = (amplitude * 0.25) * 2 * (math.random() - 0.5)
+			b0 = 0.99886 * b0 + white * 0.0555179;
+			b1 = 0.99332 * b1 + white * 0.0750759;
+			b2 = 0.96900 * b2 + white * 0.1538520;
+			b3 = 0.86650 * b3 + white * 0.3104856;
+			b4 = 0.55000 * b4 + white * 0.5329522;
+			b5 = -0.7616 * b5 - white * 0.0168980;
+			b6 = white * 0.115926;
+			a[s] = b0 + b1 + b2 + b3 + b4 + b5 + b6 + white * 0.5362;
+		end
+	end
+
+	if (draw > (sr/15)) then
+		self:queue_draw()
+		draw = 0
+	end
+
+	-- passes array a {} into buffer
+	for c = 1,#outs do
+		outs[c]:set_table(a, n_samples)
+	end
+	draw = draw + n_samples
+end
+
+function render_inline (ctx, w, max_h) --inline display
+	local ctrl = CtrlPorts:array()
+	h = 30
+	p = 0
+	inc = 0
+	ycy = 0.5
+	pink = false
+	local amplitude = ARDOUR.DSP.dB_to_coefficient(ctrl[2])
+	if ctrl[1] == 1 then pink = true end
+	if pink then inc = 0.7/w end
+
+	--draw rectangle
+	ctx:rectangle(0, 0, w, h)
+	ctx:set_source_rgba(0, 0, 0, 1.0)
+	ctx:fill()
+	ctx:set_line_width(1.5)
+	ctx:set_source_rgba(0.8, 0.8, 0.8, 1.0)
+
+	l_x = 0
+	l_y = 0
+	for x = 0,w do
+		if pink then ycy = 0.3 else ycy = 0.5 end --slant slightly like an actual pink noise spectrum
+		y = math.log(20^amplitude) * (math.random() - 0.5) - p
+		yc = ycy * h + ((-0.5 * h) * y)
+		ctx:move_to (x, yc + 3)
+		ctx:line_to (l_x, l_y + 3)
+		l_x = x
+		l_y = yc
+		ctx:stroke()
+		p = p + inc
+	end
+	return {w, h + 6}
+end