While speaking to a friend, which of the following parameters holds...

The frequency of a sound wave depends only on the source producing it and remains constant even if the medium changes. It is a fundamental characteristic of the speaker's vocal cords. Therefore, while speaking to a friend, the frequency of the sound produced holds a unique value.

Wave velocity depends on the properties of the medium.

Wavelength depends on both the frequency and the medium.

Amplitude depends on the energy or loudness of the sound, which can vary continuously.