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→Quality Considerations
Harmonizers additionally have the difficulty of detecting the pitch you are playing, which has to occur before it knows by how much to shift the pitch. This analysis requires buffering and analyzing a segment of audio, which can lead to greater latency than a simple chromatic shift. Many chromatic shifts, however, also use pitch tracking to assist in reducing artifacts and smoothing output, which again can lead to lag.
Your guitar signal isn't a periodic waveform like a perfect sine wave, but real-world audio with changing waveforms, even when a single note is sustained without vibrato. Sped-up audio segments must be repeated to consume the same amount of time as their original length. Slowed-down segments must be chopped, so they don't consume more time than the original segment. Additionally, piecing together segments can get ugly- in order to align the phase, pitch must be detected...but what about those noisy transients?
Even when using "nice" intervals like octaves, the shifting process leaves lots of artifacts in the tone. If you have two shifters available, try shifting up an octave then back down to the original note. It will likely sound nothing like the original note. Using less harmonic intervals will fare even worse. '''A good pitch shifter minimizes artifacts, or makes the artifacts somewhat musical, rather than crackly or overly alien-sounding.'''