Maybe that was why his voice almost never changed pitch.

Change of the breath air pressure also changes the pitch.

Clearly, the musician must do something to change the pitch, right?

As they moved along, the sound of the roaring water seemed to change pitch.

She changes the pitch of her voice, taking it up a notch.

By and large, the surgery does not change the pitch of the patient's voice, though some report slight changes.

More science: the location of the staples changes the pitch.

You can also change the pitch when you play it.

It seemed to have changed not only pitch but timbre as well.

The sound was not exactly continuous, but seemed to change pitch slightly, going in and out almost like breathing.