What information depends upon the particular application. One common application may be to remove noise. This was a simple way of removing noise. So that is what signals are all about. Well, they are one of the many tools for doing these things mentioned above.
CD players have nothing to do with wavelets, either.
Those types of signals are never subjected to these kinds of signal processing. Well, I'll give you an example of the type of signal processing I'm talking about. Submarines know what's going on under the sea through the use of sonar. Now, a submarine will look for other submarines via this process of sending out sounds and listening for reflections. Of course, there is no way of telling directly what the sound is being reflected off of.