Thomas D. Carrell Commun. Sci. & Disord., Northwestern Univ.,
Evanston, IL 60208-3570 While signal-to-noise ratios range from
about 50--90 dB in laboratory experiments, measurements of
speech levels in most natural environments show much poorer
listening conditions. For example, Teder [Hear. Instrum. 11, 32
--33 (1990)] measured signal-to-noise ratios ranged from a high
of 13 dB in a carpeted office to low of 1 dB in a 1986 Chevy
Nova traveling at 55 mph. These numbers indicate an immense
difference between speech signals presented to listeners in
laboratory experiments as opposed to the real-world environment.
Although speech intelligibility has been well studied in noise,
there has been little study of the acoustic characteristics of
speech that allow the message to be separated from the
background noise. One characteristic of voiced speech that shows
great promise in this regard is amplitude comodulation. In the
present research, amplitude comodulated tone-analog sentences
[Carrell and Opie, Percept. Psycho