Learn how to search and read the research literature, most of the rest is just dabbling in the shallows.
MTG Barcelona has been doing R&D for Yamaha since the 90s. They have published a lot of work on time-frequency transformation and have certainly implemented harmonizers and time stretchers. Look for papers and thesis by Jordi Bonada, Alex Loscos and certainly others too: https://www.upf.edu/web/mtg/research/publications
Needless to say pitch shifting is nothing new, so going back to research publications from the 90s may help. Publications might be found in early conferences of DAFX, ICMC, IEEE Mohonk, ACM multimedia, JAES, etc etc. Try keywords like "waveform similarity overlap add" WSOLA, "Lent's algorithm".
The musicdsp mailing list has discussed pitch shifting many times over the years. Participants have included engineers with fairly intimate familiarity with algorithms employed by Eventide, z-plane, etc. I would search the archives (you may need to do some digging to find all of the archives dating back to the late 90s).
Maybe look at expired patents from Creative Labs, Eventide and Antares if you feel comfortable exposing yourself to that literature.
MTG Barcelona has been doing R&D for Yamaha since the 90s. They have published a lot of work on time-frequency transformation and have certainly implemented harmonizers and time stretchers. Look for papers and thesis by Jordi Bonada, Alex Loscos and certainly others too: https://www.upf.edu/web/mtg/research/publications
Needless to say pitch shifting is nothing new, so going back to research publications from the 90s may help. Publications might be found in early conferences of DAFX, ICMC, IEEE Mohonk, ACM multimedia, JAES, etc etc. Try keywords like "waveform similarity overlap add" WSOLA, "Lent's algorithm".
The musicdsp mailing list has discussed pitch shifting many times over the years. Participants have included engineers with fairly intimate familiarity with algorithms employed by Eventide, z-plane, etc. I would search the archives (you may need to do some digging to find all of the archives dating back to the late 90s).
Maybe look at expired patents from Creative Labs, Eventide and Antares if you feel comfortable exposing yourself to that literature.