## 4pPP20. Intrinsic envelope fluctuations and modulation-detection thresholds for narrow-band noise carriers.

### Session: Thursday Afternoon, May 16

**Author: Torsten Dau**

**Author: Jesko Verhey**

**Location: Graduiertenkolleg Psychoakustik, Fachbereich Physik, Univ. Oldenburg, D-26111 Oldenburg, Germany**

**Author: Armin Kohlrausch**

**Location: Inst. Percept. Res. IPO), Eindhoven, The Netherlands**

**Abstract:**

This contribution summarizes analytical properties of envelope modulation
spectra of bandpass noise signals, which are relevant for the dependence of
amplitude-modulation thresholds on modulation rate and noise carrier bandwidth.
Lawson and Uhlenbeck [Threshold Signals (McGraw-Hill, New York)] showed in 1950
that the modulation spectrum, i.e., the power spectrum of the linear envelope of
a bandpass noise, has an approximately triangular continuous spectrum besides
the dc peak. For a constant overall level of a noise band, the total power of
intrinsic noise fluctuations, i.e., the total area under the triangle, remains
constant. The modulation spectrum, however, becomes broader with increasing
noise bandwidth. For low modulation rates, this leads to a reduction in
intrinsic modulation power. For higher modulation rates, the intrinsic
modulation power increases. Simple analytical calculations are presented which
compute the integrated modulation power of the noise within the transfer
function of a hypothetical modulation filter. For a set of carrier bandwidths
between 1 and 6000 Hz and for signal modulation of 5, 25, and 100 Hz the
calculated values of overall modulation power are compared with experimentally
obtained modulation detection thresholds, and with results from simulations of
an auditory model.

from ASA 131st Meeting, Indianapolis, May 1996