pitch

Meaning: Pitch is the perceived highness or lowness of a sound, set mainly by the wave's frequency: higher frequency, higher pitch. Amplitude sets intensity and perceived loudness instead. The source fixes the frequency, so when sound passes from air into water the speed and wavelength change but the frequency, and so the pitch, does not. Human hearing spans roughly 20 Hz to 20,000 Hz, and doubling the frequency raises the pitch one octave.

Equation: f = v/λ, where f is frequency (Hz), v is the speed of sound in the medium (m/s), and λ is wavelength (m).

On the MCAT: Doppler passages ask for the pitch an observer hears: an approaching source gives a higher observed frequency and pitch, a receding source a lower one. For instruments, a string sounds higher when shorter, under more tension or lighter per unit length. An open pipe has fundamental f = v/2L and a closed pipe f = v/4L, with L the pipe length (m), so shortening either pipe raises the pitch.

Common confusion: Louder does not mean higher. Turning up the volume raises amplitude, intensity (W/m²) and sound intensity level (dB) but leaves the frequency unchanged, so the pitch stays the same.