A mechanism that MIDI provides for extending the number of parameters that can be controlled via the MIDI Controller message type. A parameter to be edited can be selected by sending a registered parameter or non-registered parameter message, and then the parameter's value is altered by sending a data entry message. Registered parameter numbers (RPNs) are assigned standard meanings in the MIDI standard; for example, RPN 0 is used to set the sensitivity (range) of a synth's pitch wheel, and RPN 1 is used for fine tuning. On the contrary, non-registered parameter numbers (NRPNs) do not have standard meanings assigned; manufacturers are free to use these as they see fit. To date, only a handful of RPNs have been assigned.