Release notch-bank filter

scripts/notch_bank.lua

@@ -1,15 +1,15 @@
 ardour {
 	["type"]    = "dsp",
-	name        = "Notch Bank",
+	name        = "a-Notch Bank",
-	category    = "Example",
+	category    = "Filter",
 	license     = "MIT",
 	author      = "Ardour Lua Task Force",
-	description = [[An Example Filter Plugin]]
+	description = [[Notch Filter Bank; useful to remove noise with a harmonic spectum (e.g, mains hum, GSM signals, charge-pump noise, etc).
+Note: this plugin is not suitable to be automated, it is intended for static noise only.]]
 }
 
--------------------------------------------------------------------
+------------------------------------------------------------------
--- this is a quick/dirty example filter: no de-click, no de-zipper,
+-- this is a quick/dirty example filter: no de-click, no de-zipper
--- no latency reporting,...
 -------------------------------------------------------------------
 
 -- configuration
@@ -28,23 +28,22 @@ end
 function dsp_params ()
 	return
 	{
-		{ ["type"] = "input", name = "Base Freq", min = 10, max = 1000, default = 100, unit="Hz", logarithmic = true },
+		{ ["type"] = "input", name = "Base Freq", min = 10, max = 2000, default = 100, unit="Hz", logarithmic = true },
 		{ ["type"] = "input", name = "Quality", min = 1.0, max = 100.0, default = 8.0, logarithmic = true },
 		{ ["type"] = "input", name = "Stages", min = 1.0, max = max_stages, default = 8.0, integer = true },
 	}
 end
 
-
 -- plugin instance state
 local filters = {} -- the biquad filter instances
 local chn = 0 -- configured channel count
 local sample_rate = 0 -- configured sample-rate
+local limit = 0 -- max number of stages (given freq & sample-rate)
 
 -- cached control ports (keep track of changed)
 local freq = 0
 local qual = 0
 
-
 -- dsp_init is called once when instantiating the plugin
 function dsp_init (rate)
 	-- remember the sample-rate
@@ -56,6 +55,10 @@ end
 function dsp_configure (ins, outs)
 	assert (ins:n_audio () == outs:n_audio ())
 
+	-- explicit cleanup
+	filters = {}
+	collectgarbage ()
+
 	-- remember audio-channels
 	chn = ins:n_audio ()
 
@@ -68,7 +71,6 @@ function dsp_configure (ins, outs)
 	end
 end
 
-
 -- the actual process function, called every cycle
 -- ins, outs are audio-data arrays
 --   http://manual.ardour.org/lua-scripting/class_reference/#C:FloatArray
@@ -79,31 +81,33 @@ function dsp_run (ins, outs, n_samples)
 	-- ...and matches the configured number of channels
 	assert (#ins == chn)
 
-	local ctrl = CtrlPorts:array() -- get control parameters as array
+	local ctrl = CtrlPorts:array () -- get control parameters as array
-	-- ctrl[1] ..  corresponds to the parameters given in in dsp_params()
+	-- ctrl[] .. correspond to the parameters given in in dsp_params()
 
 	-- test if the plugin-parameters have changed
 	if freq ~= ctrl[1] or qual ~= ctrl[2] then
 		-- remember current settings
 		freq = ctrl[1]
 		qual = ctrl[2]
+		-- calc max number of states to configure/process
+		limit = math.floor (sample_rate / (2 * freq)) -- at most up to SR / 2
+		if limit > max_stages then limit = max_stages end
+
 		-- re-compute the filter coefficients for all filters
 		for c = 1, chn do -- for each channel
-			for i = 1, max_stages do -- and for each filter stage
+			for i = 1, limit do -- and for each filter stage
-				-- the parameters are    type,  frequency,  quality(bandwidth),  gain
 				-- see http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP:Biquad
-				-- for a list of available types, see
+				-- and for a list of available types, see
 				-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR.DSP.Biquad.Type
+				-- the parameters are  type, frequency, quality(bandwidth), gain
 				filters[c][i]:compute (ARDOUR.DSP.BiquadType.Notch, freq * i, qual * i, 0)
 			end
 		end
 	end
 
 	-- limit the number of process stages
-	local limit = math.floor (sample_rate / ( 2 * freq )) -- at most up to SR / 2
 	local stages = math.floor (ctrl['3']) -- current user-set parameter
 	if stages < 1 then stages = 1 end -- at least one stage...
-	if stages > max_stages then stages = max_stages end
 	if stages > limit then stages = limit end
 
 	-- process all channels