The frequency of sound is the number of oscillations per second of the particles of the medium through which the sound wave is travelling. Frequency is expressed in per second or s^-1 or hertz. Time period on the other hand is the time taken for one oscillation of a particle in the medium through which the sound wave is travelling. Time period is expressed in seconds.
The relation between frequency and period is: frequency = 1/ period or period = 1/ frequency.
Here we have the frequency of the singer's sound given as 440 Hz.
Period = 1/ 440 s
=> 0.0022 s.
The period of the singer's sound was 0.0022 s.