What characteristic makes a tone complex rather than pure?

A tone is considered complex rather than pure when it is composed of multiple sine waves rather than a single frequency. A pure tone is represented by a single sine wave, which means it produces a clean, distinct sound. In contrast, complex tones arise from the combination of several sine waves of varying frequencies and amplitudes, resulting in a richer, more textured sound that we typically hear in musical instruments or voices.

This characteristic of having multiple sine waves leads to the formation of overtones and harmonics, which contribute to the unique timbre of different sounds. For example, a piano and a flute playing the same note will sound different due to their unique complex tones created by the distinct sets of sine waves they produce.

The other options focus on different aspects of sound that do not specifically relate to the purity of a tone. Lower frequency might alter the pitch but does not determine whether a tone is complex. High amplitude refers to the volume of the sound rather than the complexity of its waveform. Lastly, uniform synchronization would imply a particular organization of sound waves but does not inherently define complexity in terms of multiple components contributing to the tone.