While I was at the beach I took pictures of the process of preparing Fractal Rovings for spinning so that they produce repeatable stripes. In hindsight, Thing Small's towel was perhaps not the best background, however, the pictures do show the process:
I want to keep the sequence so I start the split and mark both ends by tying strings to them.
The roving often gets twisted in the process and can jam so every once in a while I stand up and let it untwist. To do that I let out enough of it to hang without hitting the ground and then bunch up the skein and wrap the end around it with a half hitch so it can hang in the air and freely turn until it's untwisted again.
When I make socks split the long stripe roving as above. I split the short stripe roving into 4. The process is the same as above, except that I mark 4 ends at the start, split into 2 and then split each half into 2 again. I roll into 1 ball making sure all the pieces are going the same direction. Splitting the short stripe into 4 makes each short stripe go about 1 row when I knit socks. (why yes, I did sample and figure this out ahead of time, so you wouldn't have to).
Next I spin the short stripe on one bobbin and the long stripe on another. For socks I spin a singles with about 9 twists per inch and 40 wraps per inch. Then I ply them together - 6 twists per inch for a balanced yarn. With the roving split as described I get about 2 knitted inches of long stripe with 2 repeats of the short stripe pattern against each long stripe.
I'm not making socks with the above roving and I want longer colour runs so I'm just splitting each piece in half. If I wanted the longest colour runs I could just predraft the rovings a bit to loosen them up and then spin them as is. I think I did that with the other skein for this project - if I did I can show you the difference later... Maybe I'll do a 3rd kind of split for the last skein for this project. These skeins were destined to be a Colour Affection shawl in 3 values of the Periwinkle colourway. Other projects may push this one to the back seat for a bit. Stay tuned.
I can play with how I split the rovings to change my stripe pattern. For the shortest stripes I could split the long stripe into 4 pieces like I do the short stripe. I haven't tried it (would sort of defeat the purpose...), but theoretically I could match the short and long stripe lengths by splitting the long stripe in 4 and not splitting the short stripe at all since the long stripes are about 4 times longer than the short ones. Hmm, I have a couple of "oops" rovings I could play with...