A loudness enhancement technique for speech
We propose an application of the vocoder postfilter to increase perceived loudness of clean speech without increasing signal energy or degrading intelligibility. The critical band concept in auditory theory states that perceived loudness of a narrow-band signal will increase when the bandwidth of that signal increases beyond a critical band, even though the energy remains constant. Our post-filter technique applies formant bandwidth expansion to the vowel regions of speech without changing the vowel power to elevate perceived loudness. Vowels are known to contain the highest energy, have a smooth spectral envelope, long temporal sustenance, and for this reason are suitable candidates to target for a loudness enhancement technique. ISO-532B loudness analysis patterns and listening tests are provided to demonstrate a perceptual loudness improvement corresponding to a 2dB power gain.