if you are old enough to remember what was happening when a casette player (or even previously viynl LP) playback speed was changing, then you could understand that when the frequency of a sound changes, its pitch will also be changing accordingly. The effect can be simulated by adjusting the playback sampling rate of audio clips in OCTAVE/MATLAB.
From another perspective, if you relocate the spectrum of an audio signal (aka modulate it) into another portion, that might again change the pitch as well as distorting the harmonicity and timber. Yet when demodulated back into its original band, you will retain it perfectly back.
If you relocate it into ultrasound region, then of course you cannot hear it without demodulation back into hearable baseband.