diff --git a/scripts/_notch_bank.lua b/scripts/_notch_bank.lua
index d5662c72f6..68c1942c5a 100644
--- a/scripts/_notch_bank.lua
+++ b/scripts/_notch_bank.lua
@@ -7,6 +7,15 @@ ardour {
 	description = [[An Example Filter Plugin]]
 }
 
+-------------------------------------------------------------------
+-- this is a quick/dirty example filter: no de-click, no de-zipper,
+-- no latency reporting,...
+-------------------------------------------------------------------
+
+-- configuration
+local max_stages = 100
+
+-- plugin i/o ports
 function dsp_ioconfig ()
 	return
 	{
@@ -15,29 +24,42 @@ function dsp_ioconfig ()
 	}
 end
 
+-- plugin control ports
 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 = 100.0, default = 8.0, logarithmic = true },
-		{ ["type"] = "input", name = "Stages", min = 1.0, max = 100, default = 8.0, integer = 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 sample_rate = 0
-local chn = 0 -- channel count
-local max_stages = 100
+local chn = 0 -- configured channel count
+local sample_rate = 0 -- configured 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
 	sample_rate = rate
 end
 
+-- dsp_configure is called every time when the channel-count
+-- changes, and at least once at the beginning.
 function dsp_configure (ins, outs)
 	assert (ins:n_audio () == outs:n_audio ())
+
+	-- remember audio-channels
 	chn = ins:n_audio ()
+
+	-- set up filter instances for all channels
 	for c = 1, chn do
 		filters[c] = {}
 		for i = 1, max_stages do
@@ -46,36 +68,52 @@ 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
+-- n_samples are the number of samples to process
 function dsp_run (ins, outs, n_samples)
+	-- make sure input and output count matches...
+	assert (#ins == #outs)
+	-- ...and matches the configured number of channels
 	assert (#ins == chn)
-	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 as array
+	-- ctrl[1] ..  corresponds to the parameters given in in dsp_params()
 
-	local ctrl = CtrlPorts:array() -- get control parameters
+	-- 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]
-		for c = 1, chn do
-			for i = 1, max_stages do
+		-- 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
+				-- 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
+				-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR.DSP.Biquad.Type
 				filters[c][i]:compute (ARDOUR.DSP.BiquadType.Notch, freq * i, qual, 0)
 			end
 		end
 	end
 
-	local limit = math.floor (sample_rate / ( 2 * freq ))
-	local stages = math.floor (ctrl['3'])
-	if stages < 1 then stages = 1 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
 	for c = 1, chn do
+		-- when not processing in-place, copy the data from input to output first
 		if not ins[c]:sameinstance (outs[c]) then
 			ARDOUR.DSP.copy_vector (outs[c], outs[c], n_samples)
 		end
 
+		-- run all stages, in-place on the output buffer
 		for i = 1, stages do
 			filters[c][i]:run (outs[c], n_samples)
 		end