Trying to control audio cue levels with external OSC

[Ken Pearce]

Hello,

I'm trying to control audio cue levels by moving track faders in Reaper.  Everything works fine right up to the last step, but I can't get cues to respond to the continuous OSC values coming in.  What I've got so far, in QLab 5:

• Moving a Reaper track fader successfully outputs OSC values in decibels, which are sent to QLab on localhost port 5300.  The messages stream continuously in the QLab OSC input log when I move the slider, for example:  

               /track/1/volume/db  -0.879

• In QLab, I have an audio cue named AT1.  I can send a network cue like this and verify that I can successfully change the 0 0 level slider in cue AT1 to -20.

               /cue/AT1/level/0/0  -20

• But when I replace the fixed value of -20 with the incoming OSC value as shown below it doesn't work.  As soon as I move the fader in Reaper, the slider positions in AT1's "Levels" panel all gray out, nothing moves and there's no audio change.

                /cue/AT1/level/0/0  #/track/1/volume/db#

I thought maybe the slider level change was getting swamped with the incoming data stream, so in addition to having the network cue run for long durations I also had it loop and fire off every half second.  Neither of those worked.  I also tried just stuffing the incoming value into the name of a message cue but likewise no success:

                /cue/m1/name  #/track/1/volume/db#

Seems like I must be missing something simple!  I see the well-formatted OSC messages coming in to QLab but somehow I can't get network cues to read or apply them.  I think I've got the OSC formatting right.  

I'd greatly appreciate any help, or advice if there's a simpler and more reliable way of doing this.

Thanks!

-Ken

[micpool]

OSC queries are an internal QLab feature. You can only query parameters that are identified as queryable in the QLab OSC dictionary. 

This obviously excludes any parameters of external programs

[micpool]

Reaper is almost 100 percent user configurable, so it is possible to use Reaper Faders to control QLab sliders, although its debatable if the complications involved are entirely worth it.

I'm not a Reaper expert, but I quickly hacked this method of controlling the master slider of QLab cue "AT1" from the Reaper track 1 fader.

In ~/Library/Application Support/REAPER/OSC find the default file and duplicate it; Name the Duplicate "QLab.ReaperOSC"

open this file in text edit and edit the Track Volume Float value to TRACK_VOLUME f/track/volume/db f/cue/AT@/level/0/0



In Reaper Preferences, set up a control/OSC/web surface like this (refresh the pattern list to see your newly created file)

Screen recording attached

On Tuesday, March 10, 2026 at 11:26:01 AM UTC kenpea...@gmail.com wrote:

[micpool]

Probably worth adding that when setting up any external device or program to control QLab via OSC, unless your external can easily handle passcode generation, you will need to set up a no passcode route in Settings/Network/OSC Access



Mic

[Ken Pearce]

Mic,

Thanks for the detailed response.  Makes sense, I get it with the Reaper OSC file edit & will give it a try.

I didn't know OSC queries were limited to what's defined in the QLab library, so thanks for pointing that out!

Cheers,

Ken

[Ken Pearce]

Mic,

That was easy to implement & works great.  Simple solution, thanks again!

Ken