The main determinant of pitch is sound periodicity. A sound is periodic when it is composed of consecutive repetitions of a single short segment (the 'period'). The following figure (fig. 3.1 "Auditory Neuroscience") shows examples of periodic sounds:
Only a small number of repetitions of a period are required to generate the perception of pitch. The following sounds are all composed of the same period, which repeats itself a different number of times in each example. Each such sound is repeated a few times.
A single repeat results in no pitch sensation at all - there is nothing periodic:
With eight repeats, a clear pitch is heard:
Find out yourself what is the minimal number of repeats that is necessary in order to hear pitch!