# What is the absolute phase and the relative phase, of a signal?

I need to know what is the absolute phase and the relative phase, of a signal? and why these phases are important in the signal processing?

• if you don't have defined a moment in time that is absolutely $t=0$ then there is no "absolute phase", only relative phase. – robert bristow-johnson Apr 1 '16 at 0:01

$$y(t) = a\cdot \cos\left(b\cdot t + \phi_{t_0}\right), \quad \text{ where }\phi_{t_0} \text{is the phase at time } t = t_0.$$
• Isn't $\phi_{t_0}$ the phase at $t=0$ ?!? – Peter K. Apr 1 '16 at 11:58