Convert absolute CC data to relative CC data

[Link0126]

I have an Alesis Ion that has plenty of NRPN endless rotary encoders and I want to use these to control VSTIs.

But these knobs sends absolute NRPNs or absolutes CC. I need a relative output to control vsti without the jump that produces between the actual position of controllers in the ION and the preset position of controllers in any vsti. It also causes stops controlling the VSTi parameter when the value reaches 0 on the Ion. I need it to keep sending data onto the VSTi, hence relative.

I don't know anything about scripting, is there anything out there that already exists that will do this, or is there a work around that would be possible for me to understand, since I am not hugely knowledgable about MIDI?

[V'ger]

With Reaper's native MIDI learn, there are options to set as relative.

To use, move a knob on the plugin, then click the Param button in the FX window and - Learn.

[gofer]

But that won't magically do relative control with absolute messages.

If the ION has endless rotaries it will sure be able to output relative messages somehow? Some time ago I investigated for another user about some Alesis controller. Don't remember which it was. IIRC it was indeed only able to do relative control using NRPN, which is pretty weird for a control surface (I don't know of any receiving device or host that would work with those) - but at least it was relative control... I have no idea about how to easily solve the dilemma - other than urging Alesis to do it properly, sorry. I'm afraid you're stuck with absolute control using CC and the soft takeover feature.


That said:
For a single parameter you could just filter out the NRPN messages CC99 and 98 and only listen to the CC6 messages, but that will cancel out any difference between the several rotaries - all coming in as CC6...
Or someone writes something much more sophisticated that's able to convert the CC6 to different CC depending on the NRPN messages that preceed the CC6. Very error prone when moving multiple rotaries at the same time, though.

Still, the choice of NRPN for the rotaries must be the silliest design decision ever for a control surface!