Asinger raises his pitch one octave. what quality of the sound wave has changed? the frequency has increased. the wavelength has increased. the amplitude has increased. the speed has increased.

The correct answer is "the frequency has increased".

Explanation:

Frequency is the number of  vibrations in one second. Pitch depends on the frequency. High frequency produces high pitched note. Low frequency produces low pitched note.

In the given problem, a singer raises his pitch one octave. Here, the quality of the sound wave will change. On raising the pitch the frequency will increase.

Therefore, the correct option is " the frequency has increased".