Changes to time period and moving surfaces can change frequency.
If you consider the oscillating object that creates a wave then the time period of that oscillation will affect frequency, equation:
If a wave is reflected from a moving surface the frequency is changed. This is the Doppler Effect. Equation:
Where v is speed of moving surface and c is the speed of the wave in the medium.
Now consider the restoring force of a simple harmonic oscillation, i.e. a force that always acts towards the equilibrium. In simple harmonic motion (SHM) something surprising occurs - surprising at first glance. The force is proportional to the negative displacement as seen in this equation:
The proportionality constant is ω².
ω is the angular frequency,
The equation tells us that as displacement increases the force and hence acceleration increases. So the oscillator reaches larger speeds and can cover the increased distance in the same time.