Ways of accessing members of "control side" struct in SignalProcessor's process/vice versa?

[mrufrufin]

I'm a bit of a noob to Rust so apologies in advance...

I can't seem to find a way to access things in the struct declared in external!{} (such as pub struct XFade {} in the xfade example as the self passed into processed seems to be of type&mut SignalProcessor) from process. The reason I'd want to do this is to change some parameters on the control-rate side of the things with various methods (something like a float method or a list method) and have them effect what is going on the signal processing side of things. I've been digging through the rest of the code and still am not sure how to approach this. Is there a way to do this? Thanks!