problem with most pitch shifters is that they shift everything ~ the pitch and the spectral structure/formants (aka vocal tract resonances). As you shift up or down digitally this results in unnatural sounding pitch as the resonances are shifted relative to the pitch (higher notes have the formants become closer together, lower notes have the formants move further apart).
In most cases this does not reflect how that note would be generating resonances in a real vocal tract, i.e. the information that tells us about the voice type is distorted