Abbreviation for Non-Registered Parameter Numbers. NRPN’s are a type of MIDI Continuous Controller message that are not standardized by the MMA. Non-registered numbers can therefore be used by manufacturers in any way they see fit so long as it is documented. It’s almost like System Exclusive data except NRPN’s are easier to get to from other controllers. This allows a manufacturer to set up a device so a very specific type of message – perhaps something pertinent to a function found only on that machine – can be sent to it from any general controller capable of sending a wide range of continuous controller messages. Because these messages are defined loosely they can span across two controller numbers (using a MSB – LSB paradigm), which can give a substantially greater range of potential values.