Depends. Maybe Martin just doesn't find it a particular accent. And perhaps it isn't as there are quite a few people who have the same accent and all in all even Roman dialect is understandable up to a degree. It's not like napoletano. But the way he uses his voice.. yeah.. you can tell he's Roman.
that's like taking a cab and ask the driver to go in circles for 2 weeks straight non-stop... Not suggesting that I hv done it but just in case someone wants to know what it feels like ....