For many waves it is important to remember these points:

• the frequency of the wave is set by whatever is driving the oscillation in the medium. Examples are a speaker that sets up a sound wave, or the hand that shakes the end of a stretched string.
  
  
• the speed of the wave is a property of the medium.
  
  
• the wavelength of the wave is then determined by the frequency and speed:

  λ = v/f