Patent ID: 8200499

Claim:
A system that extends the high-frequency spectrum of a narrowband audio signal in the time domain: an interface configured to receive a narrowband audio signal; a squaring circuit that squares a segment of the narrowband audio signal to extend harmonics of vowels by introducing a non linearity in the received narrowband audio signal in the time domain; a random noise generator that generates consonants by introducing random-noise in the received narrowband audio signal in the time domain; a plurality of filters that pass a portion of the frequencies on the non-linearity and the random noise; a first amplifier that adjusts an envelope of the filtered portion of the random noise to an estimate of a high pass filtered version of the received narrowband audio signal; and a second amplifier that adjusts an envelope of the filtered portion of the non-linearity to a level of an envelope of the high pass filtered version of the received narrowband audio signal.