Discrete Fourier series Transform

Suppose an audio signal sampled at 8kHz. This means that every succesive eighth of a milliseconds one makes a measurement of the intensity of the signal. For the remainder of this text, we will assume we're working on a sample of EIGHT measurements. Here is an exemple of such a sample : 50 mV 206 mV -100 mV -65 mV -50 mV -6 mV 100 mV -135 mV We could represent it by this graph :