M-Audio 88 manual Rpn/Nrpn

Oxygen 88 User Guide  35

RPN/NRPN

Overview

RPN stands for "Registered Parameter Number" and NRPN stands for "Non-Registered Parameter Number". Non- registered parameter numbers (NRPN) are device-specific messages that enable you to control specific synthesizer or sound module parameters via MIDI, that are not accessible via standard MIDI CCs. The MIDI specification defines open parameter numbers to allow manufacturers to specify their own NRPN controllers.

The more common of these are registered by the MIDI Manufacturer Association and are now part of the MIDI specification, hence the term RPN (See Appendix A). Each NRPN/RPN has an associated 2-byte number.The two bytes allow for 128 values each. An RPN or NRPN message is made up of two parts: The MSB and the LSB message. Both of these messages together constitute an RPN or NRPN command. This allows for 16,384 values in total. MIDI controllers 98 and 99 represent the NRPN LSB and MSB respectively, while 100 and 101 represent the RPN LSB and MSB messages.

To transmit an NRPN/RPN message, these LSB and MSB controller messages are sent along with their user- specified values. A further controller message and value needs to be sent to specify the (coarse or fine) value adjustment. This is specified by controller number 6 (data entry) for coarse adjustments or number 38 for fine adjustments.

A list of NRPNs is usually given in the user manual of any device that receives NRPN messages. It is always necessary that the NRPN MSB and LSB be sent together. Both will be specified in the device manual, but typically only in Hexadecimal format. If this is the case, you may refer to Appendix C for help translating the value to decimal.

Combining Two MIDI CC Numbers for 16,384 possible RPNs/NRPNs

A single MIDI CC provides 128 values or possible selections - not enough to provide a sufficient number of unique RPN/NRPNs for all manufacturers of MIDI equipment. In order to make a large enough number of RPN and NRPN messages available for use by the many manufacturers of MIDI devices, two specific MIDI CC numbers (NRPN=98+99; RPN=100+101) are combined for RPN/NRPN selection. When combining two MIDI CC numbers this way, the 128 possibilities of the first MIDI CC multiply with the 128 possibilities of the second MIDI CC, resulting in 16384 unique possibilities - plenty of options for all manufacturers of MIDI equipment.

You can think of this as a matrix of 128x128 options, each representing a unique identifier a manufacturer of MIDI equipment may choose to use for selection of a specific parameter in their device. See the illustration below.

127

99

88

77

66

55

44

33

22

11 CC99 0

00 11 22 33 44 55 66 77 88 99 127

CC98