I used to sing in a '50's/'60's show and occasionally I would sing something that needed to be doubled.  That was a popular effect back then.  For those who don't know, that takes recording a part on one track and then recording it again - as close as possible to the first track - and then combining them.  The timing and pitch of the two tracks will vary and the result will be fuller.

There really was no way to do that in a live performance.  I had tried and didn't like chorus effects.  I wound up using an effect by TC Electronics called Voicetone D1 which worked quite well. 

Where I'm going with this is that I just tried it with my fiddle and - wow - what a sound.  I can sound like 2, or even 4, fiddles.  I'm using a mic with a low-Z  XLR connector but it could be used with a pickup and a DI.   Mine is about 5 years old so I don't even know if these are made anymore.