If the sound pressure wave repeats in a regular or periodic pattern, we can look at the wavelength of a single iteration of that pattern and from there derive the frequency of that wave. For example, if a sound traveling in a medium at 343 meters per second (the speed of sound in air at room temperature) contains a wave that repeats every half-meter, that sound has a frequency of 686 hertz, or cycles per second. The figure below shows a plot of a cello note sounding at 440 Hz; as a result, the periodic pattern of the waveform (demarcated with vertical lines) repeats every 2.27 ms: