_barry_maximizer.lua

ardour { ["type"] = "dsp", name = "Beelzebub Maximizer", category = "Dynamics", license = "MIT", author = "Ardour Team", description = [[Barry's Satan Maximizer]] }
-- this is based on swh's https://github.com/swh/ladspa/blob/master/satan_maximiser_1408.xml

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

function dsp_params ()
	return
	{
		{ ["type"] = "input", name = "Decay time (samples)", min = 2, max = 30, default = 30},
		{ ["type"] = "input", name = "Knee Point", min = -90, max = 0, default = 0, logarithmic = true},
	}
end

local env = 0
local pos = 0

function dsp_configure (ins, outs)
	self:shmem ():allocate (ins:n_audio () * 16)
	self:shmem ():clear ()
end

function dsp_run (ins, outs, n_samples)
	local ctrl = CtrlPorts:array ()
	local knee = ARDOUR.DSP.dB_to_coefficient(ctrl[2]);
	local env_time = ctrl[1];
	local delay = math.floor (.5 + env_time * 0.5);
	local env_tr = 1.0 / env_time;

	-- get data for all channels
	local i = {}
	local o = {}
	local b = {}
	for c = 1,#ins do
		local m = (c - 1) * 16
		i[c] = ins[c]:array()
		o[c] = outs[c]:array()
		b[c] = self:shmem ():to_float (m):array ()
	end

	-- process all audio samples
	for s = 1, n_samples do
		-- get max level from all channels
		for c = 1,#ins do
			local f = math.abs (i[c][s])
			if f > env then
				env = f
			else
				env = f * env_tr + env * (1 - env_tr)
			end
		end

		local env_sc
		if env <= knee then
			env_sc = 1 / knee
		else
			env_sc = 1 / env;
		end

		-- apply gain
		local idx = (16 + pos - delay) & 15
		for c = 1,#ins do
			b[c][1 + pos] = i[c][s];
			o[c][s] = b[c][1 + idx] * env_sc;
		end
		pos = (pos + 1) & 15
	end
end