##
## Schroeder's Equation noise
## Kyle Gorman <kgorman@ling.upenn.edu>
##
## Usage: 
##
## newsig = schroeder(x, snr);
##
## Based on:
## 
## M.A. Schroeder. Reference signal for signal quality studies. JASA 
## 44(6):1735--1736, 1968. 
##

function y = schroeder(x, snr)
    noise = ((rand(size(x)) > .5) * 2) - 1; % schroeder's epsilon
    y = ((1 + snr ^ 4) ^ (-.5)) * (x + (snr ^ 2) * (noise .* x));
endfunction