It's customizable; I found setting it for "sleepy" and "relaxed" produced my particular fave timbre of cat-purr.
The sound of a purring cat is one of the most comforting sounds available and can help soothe and calm you down when you're feeling stressed. Naturally, it's not just the sound that is important, but it's also the presence of the warm cuddly cat. Purrli tries to recreate both the sound and the presence of your very own virtual cat through a custom sound engine modelled after real purrs.
With a purr that delicately changes over time, Purrli aims at making the experience as real and lively as possible. Just like a real cat, Purrli will call for your attention. Just be careful when adjusting the last slider, if you don't want to be nagged in the middle of your work.
Scroll down the page and read the testimonials -- it's quite interesting to see the varied reasons people enjoy hearing a virtual cat purr, including:
My cat that grew up with me during childhood died two or three years ago, and whenever I was upset, she would come and lay next to me and purr to calm me down. She would nap with me, and her purring would help put me to sleep. I really miss that. This cat purr generator sounds just like her, and it really helps with my anxiety, especially during large projects.
I have fibromyalgia, so I am constantly in pain. This cat purr generator relaxes me and puts me to sleep. When I wake up during the night with pain, it helps me to fall back to sleep. I wish I had this years ago.
I have misophonia and work in an office. The purr generator has been a life saver. Now I can drown out the things like coughs, sniffles, throat clears, etc., that used to drive me nuts! It's comforting and helps me to focus.