UKH

Say you wanted to record a conversation on a long trail run, with as good audio quality as reasonably possible. How would you do it? Microphones on both people? What kind of recording device?

It depends on your budget, but I'd start with these...

https://www.wexphotovideo.com/rode-wireless-go-ii-1769142/?cpgnid=180076763...

Tricky....

Though not an audio specialist, I used to record ambient sound to layer onto short videos.

I always had problems with what I called 'physical' sounds (told you, not my field) by which I mean for example, in your case, the sound of any loose wires knocking against your chest as you run. Wind noise will also be a factor.

There are plenty of small, decent quality audio recorders around; I always used Tascam units coupled with Rode mics. And loads of gaffer tape to hold everything in place.

Good luck !

I'm the visual cousin to my professional audio colleagues, so no expert, but you will really struggle to not capture 'physical sounds' (as the previous poster puts it) if there's running involved. My first solution would be a lav mic on each person, but even then you're very likely to record a lot of noise from the mic bumping into person as they move. Clothing choice will probably be just as important as anything else - if you're sticking a mic physically on the person, you need it to move and bump around as little as possible.

I've seen a few people rig up dodgy rigs of GoPros on the end of a boom, attached somehow to a person. Perhaps you could experiment with a similar concept, replacing GoPro with mic? 

I'd be inclined to go for headset mics if you can find away of getting them to stay on. As said above, lavaliers will pick loads of bumping about noise. A handheld would be better, but I doubt you'd want to run with it.

The Rode wireless go that db79 mentioned is great. It comes in a twin pack so you get two tiny wireless mics and they both connect to one receiver, so you can record both people on the same recorder. You could get a set of running headphones that stay on well, and attach a boom with the Rode lavalier (optional extra) on the end of it.

Getting a clear recording needs to be your main focus, but if there's still some noise you can do amazing stuff with noise cancelling systems in post production.

Fantastic kit.