16mm optical is mono. Always.
The way the tracks work, a light is shone through the film and hits a photocell that turns the variations in the amount of light hitting it into variable electrical signals. This is then turned into a sound wave (oversimplifying here, but this is the gist).
It doesn't matter how many tracks you see when you look at it, because they're all doing the same thing, and it's just about varying the light levels that hit the sensor. There are no discrete tracks that are read separately, it's all mushed into one, thus it's always mono.
Stereo existed in Mag audio, but that was more for output to video or blowup to 35. I used to have a steenbeck with stereo heads (which was a real pain, since my stuff was in mono. It worked, but there was a lot of unnecessary noise from the unused second track.
Edited by Perry Paolantonio, 22 March 2017 - 07:39 AM.