Colour noise on Audacity

 I heard of white noise decades ago but I hadn't heard of the idea of colour noise until I spotted it in Jim Al-Khalili and Johnjoe McFadden's book Quantum Biology. I started with this article and have realised this is going to take a lot of unpacking for me. I knew that white noise is supposed to be an equal mix of all frequencies. Then I realised I could experiment with it in Audacity. Here is white noise with its frequency analysis.

Then I found pink noise. Notice that the intensity of the higher frequencies is lower.

And now Brownian noise.

Now I need to find out what spectral power density is.