Part # GTVDD2AA (the decoder) is the most compatible and takes all of the channels and puts them onto the stereo output. This unit will accept PCM or bitstream.
Part # GTVDIGAUD2AAUD only outputs the two stereo channels onto the two stereo channels. This unit MUST be used with a device that outputs PCM.
PCM Definition: PCM stands for Pulse Code Modulation. PCM technology is a means by which standard audio signals (which are represented by waveforms) are converted to digital audio signals (which are represented by 1's and 0's - much like computer data) with little, or no, compression. The method of audio conversion is used on most digital audio formats, including CDs and DVD-Audio, and is also used to some extent in Blu-ray and HD-DVD applications. The PCM signal is converted back to analog form for distribution to loudspeakers. PCM, although digital in nature, should not be confused with a Dolby Digital or DTS Bitstream, which is compressed, and digitally encoded in a different manner than PCM. However, Dolby Digital and DTS encoded audio signals can be decoded into PCM signals and transferred via HDMI to a growing number of Home Theater Receivers for further processing and amplification. This is common in most Blu-ray and HD-DVD player applications.
Bitstream Definition: A Bitstream refers to binary bits of information (1's and 0's) transferred from one device to another. However, in Home Theater applications, Bitstream refers to a digitally-encoded Dolby Digital or DTS-related compressed audio signal from a source component (such as a DVD, Blu-ray, or HD-DVD player, HD-Cable, or HD-Satellite Box) to a Preamp/Processor (either standalone or built into a Home Theater Receiver) for decoding and distribution to the amplifier stage for final sound reproduction, in analog form, by the loudspeakers. The Bitstream can be sent via Digital Optical, Digital Coaxial, or HDMI interface.