Why do I need to apply a window function to samples when building a power spectrum of an audio signal?

Question

I have found for several times the following guidelines for getting the power spectrum of an audio signal:

• collect N samples, where N is a power of 2

Answer 1

If you're not applying any windowing function, you're actually aplying a rectangular windowing function. Different windowing functions have different characteristics, it depends on what you want exactly.