There are several free software programs that usually outperform
any of even the expensive sound machines (or audio generators).

One of my favorites is:
Aire Freshener 2.0
It's a neat little program that has a bunch of ambient noises/windchimes / white and pink noises.  It runs out of the toolbar with a console for picking over 100 sounds (e.g., Day Surf and Thunderstorm, hearbeat), and includes adjustments. It has some nice white and pink noises, and there is even a rock star crowd noise...
It can be downloaded from numerous sites. Use the Link above, or copy the following address into your browser window:

EZAir :Here's a link for EZAir, a neat paced breathing program...
It a multipurpose program that allows selecting sounds that it provides (white noise sounds), or using your own (many can be downloaded in links below), coordinates it to a breathing pattern that you display with a customizable bar graph and pictures, and it interfaces with bioexplorer and other good biofeedback software as well. Use the link above, or copy this address into your web browser

There are many other freeware or shareware (small contributions accepted or requested

if you like the software) programs as well.

Here is another example:


This one is just a grouping of various forms of natural sounds as mp3's,
Partners in Rhyme

Here's a free white noise player (with options)


Here's a page that includes a collection of programs

Here's another shareware program