Jeri, volume and pitch aren't exactly related, but volume does affect what you hear. And some people have difficultly distinguishing pitch and volume, or being able to tell the difference in pitch between two notes if the volume is different. In the wave form, pitch = frequency and volume = amplitude.

At louder levels, you (i.e. most people) can hear higher and lower frequencies better. At softer levels, you usually only hear the middle of your frequency range. "Your" frequency range is the range of frequencies you can hear, which depends on your ears and your age. Young kids can often hear as low as 15Hz and up to 20,000, most adults hear between 40-15,000 and may have individual strengths and weaknesses or damage at various frequencies.

Ear plugs, fingers in the ears and other kinds of hearing protection usually filter out more high frequencies than the rest of the spectrum, partially because higher frequencies cause damage more easily, and partially because the plug blocks smaller wave forms from entering the ear. So in addition to cutting amplitude (volume), they can affect frequency range.

Every voice and instrument not only has a frequency range, but a signature within that range. An individual's frequency signature could, in theory, be affected by the volume. And when a singer sings a note, they don't just hit the exact frequency that relates to that note -- it's a mish-mash of frequencies based on their individual signature. I'm not sure if that could come through as a difference in pitch though -- if it does, it would be VERY slight.

The Doppler Effect, is the perceived frequency (f ´) is related to the actual frequency (f0) and the relative speeds of the source (vs), observer (vo), and the speed (v) of waves in the medium by
f´ = fo(v+vo/v+vs)
(The pluses should be plus or minus signs.) In other words, it's a shift in frequency and wavelength caused by direction and movement. A similar phenomena, but not volume related.