I'd like to use in camera slomo but I need a solution to record audio
It's possible to use an external recorder like zoom H4n or Sony PCM 10?
There is the possibility to go with start and rec camera button?
I'm a newbe with EX1r and I need some advice
There are video/audio recording devices that will detect the start-stop signal that is output from the EX1R's SDI port, but these are probably more money than you're willing to spend just to have video/audio sync. FOr slo-mo I would simply buy something like you've already mentioned and just push the 2 record buttons at the same time. In post you can slide the extra audio around in your NLE to get what you want.