I don't know if it's a uniform pitch shift for me, but high doses of 25i tend to distort/muddle the sense of pitch and melody in music for me far more dramatically than almost any other psychedelic I've taken (perhaps the most dramatically, if I thought about it more). This basically exemplifies my general problem with 25i: the dose sweetspot is just too hard for me to hit. When I hit it, everything sounds awesome, very distorted yes, but in a way that really enhances the music/gives it this otherworldly feel and presence, and I experience other positives commonly associated with the drug (laughs, introspection, lack of bodyload, etc). Get the dose too high - which I do more often than not, sadly - and everything gets freaky, uncomfortable, and concerning the sensory, often times just nastily unpleasant. The "otherworldly" distortion of my sweetspot 25i dose ramps up into hypergear and everything sounds incoherent, jumbled, discordant and often malicious sounding - the voices of the songs have often resembled alien, distorted evil whispers snaking their way into my ears. With this change in sound comes a horrible persisting nausea and sensory overload. I will tell you this, I have had plenty of difficult trips that were too intense, on many psychedelics, and I will that there is one thing that is totally unique to 25i overdoses: I will always turn the music off. Every other OD/bad experience with a psychedelic, and the music is always the ONLY positive aspect I can cling to, since it sounds cool as fuck. Not so with 25i.
I'm aware that this might be an idiosyncratic or relatively rare reaction to 25i. If anyone has experienced anything similar, though, I'd be fascinated to know. Interestingly, a lot of people have compared 25i to DOI - but with the addendum that 25i is a gentler version of DOI. Interestingly, I did note the similarities, but I thought just the opposite, that DOI was a gentler (but longer) version of 25i.