Most are crap. I can identify 3 sub-categories. Some producers have CDs in several categories:
1. Outdoor recordings, often by audiophile enthusiasts. Quality is usually absolutely brilliant. No human generated noises. I can definitely recommend Gordon Hempton; Echoes of Nature series; Dan Gibson (sounds of nature); www.soundtracker.com. In Australia, we have Les Gilbert; www.listeningearth.com (both excellent).
2. Natural sounds + music. Usually the ocean, rivers, rain, birds, frogs, assorted insects overlain with pan flute harmonies. This is the music you hear in candle shops. The natural sounds are often 'canned'. It is these which give nature sounds CDs a bad name. For best quality try 'Orange Tree Productions National Park Series', Dan Gibson (sounds+music). In Australia we have Ken Davis, Tony O'Connor; Brett Nielsen. Some are very cheap and abundant second hand because they come in sets of 10-20. There are lower quality ranges (to me) like Gentle Persuasion; Natures Harmonies; Natures Magic; Natures Symphony; Tranquility.
3. Educational recordings like 54 bird calls, 35 frog calls, etc. A search of the bird and frog appreciation organization's shops will locate these these. Often priced at full retail. Usually each sound is separately indexed and the bird/frog/insect named on the cover. Quality ranges from historic to excellent. The sounds never repeat so not as boring as you may think. Never, never, buy one with a spoken commentary - they are absolutely patronising to listen to. In Australia, we have www.naturesound.com.au (all their CDs are excellent).
I have accumulated over 200 CDs of this genre - because they are so cheap - but many are only suitable for listening when reading, studying, (ie Muzak).
