Okay so you will need a full featured audio editor, I just checked Audacity and the required features aren’t there unfortunately. I used Audition but there are a few others that will do the job too.
We know that C2 is 65.406hz (or at least so Google tells me). Using a little maths we can calculate the exact duration needed to make any sample play as a C2.
Sampling rate (Hz) / Note frequency (Hz) = Samples per cycle
These are 44100Hz samples, so…
44100 / 65.406 = 674.250069 samples
If the original sample is cropped or timestretched to 674.250069 samples in length, then it will play as C2 when looped.
So in a nutshell, use an audio editor that has a ‘duration in samples’ view and also a timestretch function that can have duration in samples too. Timestretch the wave to the above value and then once its back on your Octatrack, you’re good to go!