The pitch corrections stuff works by using Fourier Transforms to determine what frequencies of a sound have the most energy at any given moment, which can be us

The pitch corrections stuff works by using Fourier Transforms to determine what frequencies of a sound have the most energy at any given moment, which can be used to determine pitch. Then, to transform the pitch, they (most likely) use an algorithm/process called Granular Resynthesis (not to be confused with Granular Synthesis, which is related but used for a very different purpose).