REALTEK - the name itself shows that it is a software giving you a real effect. Realtek AC'97 Audio 6.0 is a windows driver, without which your computer would be literally deaf and dumb. These drivers include a recording software named AVRACK. It gives you 12 different options for playback, that is: Volume control, Wave, SW Synth, 3D Depth, S/PDIF, Aux, TV Tuner Audio, CD player, Line In, Microphone, Phone Line, Pc speaker - so in short it gives you options for all that you can imagine or connect to your computer.
For recording there are 9 different modes: Mono Mix, Stereo Mix, Aux, TV Tuner Audio, CD player, Line in, Microphone, Phone line. These are options for anything you can think of for communicating with other people. Realtek is amazingly user friendly and has compatibility with most of the modern sound devices. Although it is very good, it has installation difficulties, as there are different setup files for different versions of windows. Also, if not installed properly, it might stop working at some moments and start on its own later.