1. Global Transpose
There's a Global Transpose control on the front panel of the module that will transpose any loaded loop up or down by the chosen number of semitones. Since REX loops are made up of audio slices, this is performing some real-time pitch shifting but keeping the tempo exactly the same. Use it to change the key of any melodic loop or to change the character of beats, which aren't melodic as such. This control transposes all loops loaded into this instance of Dr Octo REX.
2. Focus in on a Loop
Click on the Show Programmer arrow to expand the lower section and get at the good stuff. Here you will see a control to alter the transposition setting and the volume of an individual loop as opposed to all loops currently loaded. So you can use this for example to load two instances of the same loop and tune each one differently to create variations when building your track. You can also click on the small keyboard area here to quickly choose which key to transpose the loop to.
3. Edit Individual Slices
In the slice area you will see a display showing the different slices in the loop, and a melodic loop will tend to have fewer, longer slices with beats having more and shorter slices. You can click on any slice to select it and then from the row of dials underneath, quickly change a range of parameters including pitch, pan, level, reverse, filter frequency and so on. This is a quick and easy way to tweak and fine tune a loop without having to do any MIDI editing: the changes are happening live inside the module. The last dial is called Output and you can use this to send any slice to any of the module's 8 outputs, and so process them differently through separate effects and mixer channels if you like.
4. Use Loop and Slice Envelopes
By switching to Slice Edit mode in this section you can select any parameter by clicking on its name and then use the pen tool to draw in envelopes over time. This is great fun: try for example drawing in a pitch or volume curve over the duration of the loop to quickly turn an acoustic guitar sound into something weird and synthetic. Or, use it to automate reverse on/off for different slices to get an equally creative result.
5. Stick to the Classics
The sections to the right of the module are more straightforward but you can still use these do tweak the sound of the module as a whole. Change filter settings and envelopes as well as LFO and amp envelope controls to shape and sculpt the sound. Combined with changes you may have already made in other areas of Dr Octo REX you will soon be creating amazing sounds from even the most basic of REX loops.