Sound, frequency and wavelength

Sound is a pressure variation travelling through a medium. Frequency in hertz describes repetitions per second: lower frequencies sound lower in pitch. Amplitude describes the size of the variation, not pitch.

Wavelength is λ = c / f. At about 343 m/s, a 100 Hz tone has a wavelength of 3.43 m. Room dimensions therefore matter strongly at low frequencies. The assumed speed is approximate, for air near 20 °C.