Low samplerate file playback in Reaper questions

[divedive]

Sometimes I work on projects where I need to render speech files to low sample rates - sometimes as low as 8kHz. In order to make speech more intelligible, I need to then edit/master files at that sample rate, boosting consonants, etc.

I don't fully understand how Reaper's playback engine works, other than you can mix many formats. As I understand, it resamples different formats to my project sample rate on the fly, right? So if my playback sample rate is 48 kHz and I'm working on an 12kHz file, for exampe, Reaper will resample the 12k file up to 48k output buffer?

And, since we're upsampling, that would probably sound 'very' close to as it will when the final platform plays it back at the correct sample rate?

Also - is it possible to downsample a file or lots of files in place on a track? IE I edit a bunch of speech at the recorded sample rate (48kHz source files in 48kHz playback) then I duplicate the track and resample all those files down to 12kHz and then master them right there in the same 48kHz session? How would you do this? A resampling plugin?

Thanks!