A warped bandwidth expansion filter
A warped filter is presented as a new speech enhancement method to adjust formant bandwidths on a critical band scale. The warped filter enhances perceived loudness without adding signal energy by exploiting the psychoacoustic nature of the auditory system. The critical band concept in auditory theory states that when the energy in a signal remains constant, loudness increases when the energy spreads beyond a critical bandwidth. A warped filter is proposed and developed to elevate the perceived loudness of clean speech by applying nonlinear bandwidth expansion to the formant regions of vowels in accordance with the critical band scale. The filter has been inspired and motivated by the biological representation of loudness in the peripheral auditory system and the critical band concept of hearing.