SPDZ protocol: how expensive is it to generate the multiplicative triples?
The answer to your question can be found in a SPDZ follow up paper; it is described as contribution (2) in the intro (top of page 2).

There is a new version of SPDZ called MASCOT that uses OT instead of somewhat homomorphic encryption, and is supposed to be about 200 times faster. So, I would recommend looking at that as well.