AC-3 is the most common version containing up to 6 total channels of sound, with 5 channels of full-bandwidth of 20 Hz - 20 kHz-normal range for speakers (front left and right, center, front, right rear and left rear) and one dedicated output channel for low frequency sounds known as low frequency Effect, or subwoofer. The Dolby Digital format also supports the use of Mono and Stereo. The AC-3 is one of the so-called perceptual compression formats. What it does, basically, is to remove all parts of the original sound, encoded analog, which can not be perceived by the human ear. In this way, it is achieved that the same information is smaller and therefore take up much less physical space. Once achieved compression of the original wave, you can add more information that was not previously possible.
Windows Media Audio (WMA) is an audio data compression technology developed by Microsoft. The name can be used to refer to its audio file format is audio codecs. It is a proprietary technology that forms part of the Windows Media framework. WMA consists of four distinct codecs. The original WMA codec, known simply as WMA, was conceived as a competitor to the popular MP3 and RealAudio codecs. WMA Pro, a newer and more advanced codec, supports multichannel and high resolution audio. A lossless codec, WMA Lossless, compressed audio data without loss of audio fidelity (the regular WMA format is lossy). WMA Voice, targeted at voice content, applies compression using a range of low bit rates.