1. A system that extends the high-frequency spectrum of a narrowband audio signal in the time domain comprising: an interface configured to receive a narrowband audio signal; a controller that extends the harmonics of vowels by introducing a non linearity in the received narrowband audio signal in the time domain; and a random noise generator that generates consonants by introducing random-noise in the received narrowband audio signal in the time domain, where the controller comprises a squaring circuit that squares a segment of the narrowband audio signal.