What are layers?
The best analogy is to the way cartoons used to be animated. Each component of a scene would be painted on a transparent film, and then each film would be stacked or layered over the other to produce the complete composition. In this way, you could easily animate a person walking because his legs could be animated independantly of his body, for example. Similarly, complex images can be broken down to layers within GIMP and each layer can be processed independentlly of every other. See the Layers section in the manual for more information.
While both are decoding systems for home theatre sound, Dolby Digital is the successor to Dolby Pro-Logic. Pro-Logic is the more commonly found of the two systems and is used on videotapes, Laserdiscs and even DVD. Pro-Logic is actually four channels of sound that are reproduced through five speakers. The four channels are: Left, centre, right and surround. The surround channel consists of two speakers, and in Pro-Logic, the same sound comes from both speakers. Pro-Logic is typically an analog system. Dolby Digital is a discrete digital system, which offers six separate channels of sound, with a dedicated subwoofer channel used for deep bass. The six channels are: Left, centre, right, left surround, right surround and LFE (or Low Frequency Effect) for bass. Dolby Digital is also known as 5.1-channel sound and has been declared the audio standard for DVD and HDTV. It offers greater dynamic range than Pro-Logic, better frequency response and improved separation between channels.
