I am new to IPlug and trying to make a basic plug-in. I am wondering how I could duplicate the input sound so that I can pitch it up or down, separately from the main sound. Both will play simultaneously. I am unsure of how to go about doing this.
Welcome! This is quite a vague and open ended question that suggests to me that you may be trying to run before you can walk. You are describing mixing a pitch-shifted version of the signal with the dry signal.
There are several ways to achieve pitch shifting with different trade-offs and complexity. Here is a good site describing different methods: http://www.katjaas.nl/pitchshift/pitchshift.html
You could use a 3rd party library to do the pitch shifting. There are several commercial and free options. IPlug2 includes the WDL repo, which has a pitch shifting engine that is used in Reaper
Great, I will check these out. Thank you!