We present an analytical formalism for the description of Blazhko RR Lyrae light curves in which employ a treatment for the amplitude and frequency modulations in a manner similar to the theory of electronic signal transmitting. We assume monoperiodic RR Lyrae light curves as carrier waves and modulate their amplitude (AM), frequency (FM), phase (PM), and as a general case we discuss simultaneous AM and FM. The main advantages of this handling are the following: (i) The mathematical formalism naturally explains numerous light curve characteristics found in Blazhko RR Lyrae stars such as mean brightness variations, complicated envelope curves, non-sinusoidal frequency variations. (ii) Our description also explains properties of the Fourier spectra such as apparent higher-order multiplets, amplitude distribution of the side peaks, the appearance of the modulation frequency itself and its harmonics. In addition, comparing to the traditional method, our light curve solutions reduce the number of necessary parameters. This formalism can be applied to any type of modulated light curves, not just for Blazhko RR Lyrae stars.