Thanks for that. in & accum make sense. out only seems to allow integer increments, and it’s not clear how that translates to the range in the controlspec for something like the freq range

cs_LPF_F = controlspec.new(10,20000,‘exp’,0,1200,‘hz’)
params:add{type=“control”,id=“lpf freq”,controlspec=cs_LPF_F,
action=function(x) engine.lpf_freq(x) end}