add a notch-bank filter

scripts/_notch_bank.lua

@@ -0,0 +1,63 @@
+ardour {
+	["type"]    = "dsp",
+	name        = "Notch Bank",
+	category    = "Example",
+	license     = "MIT",
+	author      = "Ardour Lua Task Force",
+	description = [[An Example Filter Plugin]]
+}
+
+function dsp_ioconfig ()
+	return
+	{
+		{ audio_in = 1, audio_out = 1},
+	}
+end
+
+function dsp_params ()
+	return
+	{
+		{ ["type"] = "input", name = "Base Freq", min = 10, max = 1000, default = 100, unit="Hz", logarithmic = true },
+		{ ["type"] = "input", name = "Quality", min = 1.0, max = 16.0, default = 8.0 },
+		{ ["type"] = "input", name = "Stages", min = 1.0, max = 20, default = 6.0, integer = true },
+	}
+end
+
+local filters = {} -- the biquad filter instances
+local freq = 0
+local bw = 0
+
+function dsp_init (rate)
+	for i = 1,20 do
+		filters[i] = ARDOUR.DSP.Biquad (rate)
+	end
+end
+
+function dsp_run (ins, outs, n_samples)
+	assert (#outs == 1)
+	assert (n_samples < 8192)
+
+	-- this is quick/dirty: no declick, no de-zipper, no latency reporting,...
+	-- and no documentation :)
+
+	local ctrl = CtrlPorts:array() -- get control parameters
+	if freq ~= ctrl[1] or bw ~= ctrl[2] then
+		freq = ctrl[1]
+		bw = ctrl[2]
+		for i = 1,20 do
+			filters[i]:compute (ARDOUR.DSP.BiquadType.Notch, freq * i, bw, 0)
+		end
+	end
+
+	if not ins[1]:sameinstance (outs[1]) then
+		ARDOUR.DSP.copy_vector (outs[1], outs[1], n_samples)
+	end
+
+	local stages = math.floor (ctrl['3'])
+	if stages < 1 then stages = 1; end
+	if stages > 20 then stages = 20; end
+
+	for i = 1, stages do
+		filters[i]:run (outs[1], n_samples)
+	end
+end