From Google 
“Oscillator sync is a feature in some synthesizers with two or more VCOs, DCOs, or “virtual” oscillators. As one oscillator finishes a cycle, it resets the period of another oscillator, forcing the latter to have the same base frequency.”
Here also more info regarding this “technique”
Hope it helps 
there might be better groove boxes
there might be better synths
but for me A4 is the best combination of a groove box and a synth
Change the Pulse phase/PWM to explore this further.
What an inspiring and enjoyable set. Those A4s are well and truly rinsed. 
Big boy arrived today. The demo I bought was defective and when I tried to return it, they sent me a new one. Sweet!
To think, just a month ago I was thinking of parting with this synth, and now I have two! Although I don’t know if I will keep the MK1, unless I give up trying to get Transfer to work and keep it for the unfinished projects on there… and double the voices.
Check the MKI 4 outputs mod.
Cheaper solution if you know how to solder…
Set the 2 ocs with same level.
Activate Sync, and tune up osc 1 or 2 depending on Sync mode.
(change osc 2 tune for Sync 1>2 iirc)
I had fun with Sync on 4 track with lfo on osc 2 pitch…
Gary is supreme on the A4, he just jumps on it films and makes inspirational sounds. He also has some tutorials on the A4 on his YouTube page. Really friendly and helpful person too.
Cheers for that - soldering puts the fear in me - will stick with one a4 mk1 for now and maybe add another voice with a cheap td3 which sounds pretty good - then maybe a cheap sampler Volca or something and run them both through the a4 inputs - use the usb (which sounds ‘like tape’) and have six tracks to kick around
Sync can get wild on the A4, it’s one of my favourite things to explore. Not figured out a use for the ‘Metal’ mode yet (seems like a dirtier 1>2 to me…) but as already said here, modulating pitch, pw, or the sync amount itself can be really interesting…
Oh boy, how much I’d love to see that patch! 
I didn’t get it too. Sync 1>2 is easier to understand…
i’ve been messing around with Metal sync and have found some of the areas where it becomes interesting. it sounds great at certain settings, sort of like a superfast crossfader-sync, zipping quickly between the ‘live’ osc (osc2, volume 100) and its controller (osc1, silent)…
Awesome work.
Yesterday my Boss RC500 looper arrived. I combine it with my a4 mk2 and my mixer. This looper is very simple to use, also I can use my dj mixer almost without using brain capacity. So all focus on the A4.
It has always been a hassle to do song transition on my a4
an OT next to it overloads my brain with possibilities and stops me from making music
It took me an hour to understand how to make good quantized loops,
but now it works like a dream!
RC 500 slave or master ?
I have one. Had some crashes slaved, but I was sending CCs and midi notes from OT.
BTW you can play its pretty good sounding drums with A4 CV/FX tracks, midi send on.
gonna have an A4 video coming sometime soon, brought it with me to visit my fam / film in the US. but I lost one of the knobs on the way over. Maybe when i took it out at airport security. crying commences now
