Fred always comments that his mother's and sister's voices sound alike on the telephone. Both voices are equally high-pitched and loud. Yet, he is able to tell the voices apart by a subtle difference in their voice quality. This difference is most likely due to the feature of sound known as _____.

The timbre is associated with the waveform and allows us to distinguish sounds of the same frequency produced by different instruments or similar voices from different people. The tone is characterized by the composition of frequencies that constitute the sound wave emitted by the instrument, or by the voice. The tone is also called sound quality. For this reason, when Fred says he can differentiate his mother's voice from his sister's because of the difference in voice quality, Fred is referring to the Timbre.