Do non periodic signals have frequency? Because my pretty general rule f = 1/T says that they have zero frequency. But suppose i analyze a voice signal. We generally associate a term frequency with them. If you ever had used audacity you might have noticed that the graph is quite random and its nearly impossible to find any periodicity in them. Then why don't they have zero frequency? I hope that you understand my post because my English is not so good as i am not a native English speaker.