another lua DSP example

scripts/_smash.lua

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+ardour { ["type"] = "dsp", name = "Sound Smasher", category = "Dynamics", license = "MIT", author = "Ardour Lua Task Force", description = [[Another simple DSP example]]
+
+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
+
+
+-- the DSP callback function to process audio audio
+-- "ins" and "outs" are http://manual.ardour.org/lua-scripting/class_reference/#C:FloatArray
+function dsp_run (ins, outs, n_samples)
+	for c = 1, #outs do -- for each output channel (count from 1 to number of output channels)
+
+		if not ins[c]:sameinstance (outs[c]) then -- if processing is not in-place..
+			ARDOUR.DSP.copy_vector (outs[c], ins[c], n_samples) -- ..copy data from input to output.
+		end
+
+		-- direct audio data access, in-place processing of output buffer
+		local buf = outs[c]:array() -- get channel's 'c' data as lua array reference
+
+		-- process all audio samples
+		for s = 1, n_samples do
+			buf[s] = math.atan (1.5707 * buf[s]) -- some non-linear gain.
+
+			-- NOTE: doing the maths per sample in lua is not super-efficient
+			-- (vs C/C++ vectorized functions -- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP)
+			-- but it is very convenient, especially for prototypes and quick solutions.
+		end
+
+	end
+end