NRPN is Non Registered Program Number.
An NRPN is a series of hex numbers used to stack MIDI control commands to make devices respond to commands not defined by RPN (registered program number).
For example, I cannot get Sonar 4.0.3 to access the alternate banks of my Alesis NanoSynth. Changing patches to other Bank 0 does not make a change in the synth. I know the synth works properly, because I can change banks through all 640 patch combinations from my Hammond XR2 console.
I want to try NRPN with Sonar, to see if that will let it control the banks other than Bank 0 in my synth.