Hi everyone including Mike and Pat,
Attached is an example of how to map midi note numbers to the frequencies of any arbitrary tuning, for use with any pd synth.
The tuning file is stored externally and is easy to specify as plain ASCII text -- 128 of numbers with one pitch per line where the pitch is such that a standard middle C is 60.000 and a standard A440 is 69.000.
There is no synthesiser here as this is a bare bones example of microtuning
up to those with an interest to patch this into their pd synths.
The example tuning file used is simply Gioseffo Zarlino's 2/7 Comma Meantone of 1558, for those curious.