Creation of Brownian noise as random walk I am trying to create brown noise by integration of white noise (random walk).

I created Gaussian white noise. The histogram shows Gaussian distribution and Welch (and also FFT) shows flat spectrum. 

Now I try to integrate it

$x(k+1) = x(k) + q(k)$

where $q$ stands for white noise and $x$ for resulting Brownian noise.

But the resulting spectrum is

According Wikipedia I would expect that there should be straight line in the plot.

What I am doing wrong?
So this question does not remain as unanswered:

Making your horizontal scale into log-scale should give you the decade drop and yield the linear amplitude graph.