lucaduke:
My question is: basically i have to sample a digital signal every 0,48us.
Well, you probably can. You can speed arduino up to 20MHz and maybe a little more, but . The problem is, you will not be able to store or even process your data - atmega328 has too tiny a RAM and you will get to the very edge of performance by just reading it.
But what you can do is to wire your signal to the asynchronous counter and maybe measure the duty cycle of your DATA. This way you'll need much more manageable speeds, so MAYBE you will get what you need. But I don't see any way to sync it to your CK.
By the way, what is your final goal? A sound recorder?