Digital Speech Signal
Switches composite signal (ANSI and ICRA) on/off intermittently.
Presented in bursts 300 ms wide.
The rate of the intermittent signal is randomly varied.
ANSI Spectrum (1997): drops 6 dB/octave above 900 Hz.
ICRA (International Colloquium of Rehabilitative Audiologists): flat to 500 Hz and then falls at rate of 10 dB/octave