# why nonperiodic signals still has the concept of frequency?

I'm new to EE from CS background, just a question on nonperiodic signals. I don't understand why nonperiodic signals still has the concept of frequency/frequency domain? The definition is :

Period refers to the amount of time, in seconds, a signal needs to complete 1 cycle. Frequency refers to the number of periods in 1 s

Since nonperiodic signal doesn't have cycle(does't form a pattern), therefore it shouldn't have the concept of Frequency neither?

• How familiar are you with the concept of the Fourier or Laplace transforms? Oct 4, 2019 at 2:50
• A non-periodic signal (or any signal really) is made up of a combination of periodic signals (sinusoids) of varying amplitudes, frequencies, and phase shifts. Any signal you can imagine can be produced by superimposing the right combination of sinusoids of the appropriate amplitude, frequencies, and phase shifts. Oct 4, 2019 at 2:55
• @Hearth not at all. Oct 4, 2019 at 3:46
• frequency is just the periodicity of the best-correlating basis function Oct 4, 2019 at 4:29
• 'not at all' ? But you were talking about Frequency domain. Whats the representation of a signal in Frequency domain called ? Oct 4, 2019 at 6:16