AAC is a state-of-the-art audio compression algorithm that provides compression superior to that provided by older algorithms such as AC-3. AAC and AC-3 are both transform coders, but AAC uses a filterbank with a finer frequency resolution that enables superior signal compression.

Both provide 5-channel audio coding capability, however AAC provides a factor of two better audio compression relative to MPEG-2 BC, and is appropriate in all situations in which backward compatibility is not required or can be accomplished with simulcast. An MPEG-1 two channel decoder can decode an MPEG-2 BC 5-channel bitstream.

Most DVD-Video discs contain Dolby Digital soundtracks. However, it's not required. Some discs, especially those containing only audio, have PCM tracks. It's also possible for a 625/50 (PAL) disc to contain only MPEG audio, but so far MPEG audio is not widely used. Don't assume that the "Dolby Digital" label is a guarantee of 5.1 channels. A Dolby Digital soundtrack can be mono, dual mono, stereo, Dolby Surround stereo, etc.

The MPEG-2 AAC standard is a new, state of the art audio standard that provides very high audio quality at a rate of 64 kb/s/channel for multichannel operation. It provides a capability of up to 48 main audio channels, 16 low frequency effects channels, 16 overdub/multilingual channels, and 16 data streams. Up to 16 programs can be described, each consisting of any number of the audio and data elements.

Dolby Digital AC-3 is a technology developed by Dolby Laboratories that allows us to store much more CD-quality audio in much less space than traditional CD-audio. Dolby Digital also allows us to present soundtracks in the home that offer a complete surround sound experience, just like at the movie theatre, with left, centre, and right channels, stereo surround channels and a subwoofer.

Dolby Digital (AC-3) is a digital sound compression technique developed by the Dolby Laboratories Licensing Corporation. Supporting 5.1-channel surround sound, as well as stereo (2-channel) sound, this technique enables a large quantity of sound data to be efficiently recorded on a disc. However, nowadays, the understanding has become to be Dolby Digital (AC-3) = Dolby Surround = Dolby Digital 5.1.

Dish Network currently only provides Dolby Digital soundtracks on their ‘home theater’ Pay-Per-View channels 512-513 on the 119 satellite and PPV channels 520-525 on the 110 satellite. You can look for the “DD” symbol in the Electronic Program Guide (EPG) to see if the movie is broadcasted in Dolby Digital. These channels also show some movies in their original letterbox format. DISH Network will expand their DD offerings through time.

MPEG-4 AAC has all the tools and functions of MPEG-2 AAC plus the Perceptual Noise Substitution (PNS) tool, a Long Term Predictor (LTP) as well as extensions to support scalability. Therefore all MPEG-4 AAC decoders can decode MPEG-2 AAC bitstreams, and conversely MPEG-2 AAC decoders can decode MPEG-4 AAC bitstreams if none of the MPEG-4 extensions are signalled.

MPEG-2 AAC comes in 3 different "flavors", called profiles, which are coder configurations with different complexity and performance. They are derived from each other by different parametrization of certain algorithmic parts of the AAC coder.

There are three profiles for the AAC standard, called Main Profile, Low Complexity Profile, and Scalable Sampling Rate Profile. The Main profile is intended for use when processing power, and especially memory, are not at a premium. The Low Complexity profile is intended for use when cycles and memory use are constrained, and the SSR profile when a scalable decoder is required.

The decoder source is complete and fully compliant and is capable of decoding all three AAC profiles: Main, Low Complexity and Scaleable Sampling Rate. It is a general multi-channel decoder capable of decoding up to 48 audio channels, 15 auxiliary low frequency enhancement channels and 15 data streams. Furthermore, it is quite efficient in that the compiled reference source coder decodes a stereo bitstream in real-time on a 100 MHz Pentinum.

The files should coded by CBR (Constant Bit Rate). (Currently, VBR (Variable Bit Rate) is not supported) In case where audio stream is MPEG AAC ADTS and rate control is CBR, bit rate should be multiples of 8kbps.

Dolby Surround AC-3 does not use matrixing and the five audio channels have complete separation. Sadly, this is not sufficient for realistic surround sound reproduction, the problem being the "pair-wise" mixing style. Dolby Surround AC-3 is just a delivery mechanism and is not tied to pair-wise mixing, however, to date all Dolby Surround AC-3 movie sound tracks have been mixed using the pair-wise mixing style.

Ambisonics cannot contribute to the Dolby Surround AC-3 encoding or decoding processes; it can make contributions before the 5.1 discrete channels are encoded and after they are decoded. Dolby Surround AC-3 is described in technical publications available on the Dolby Laboratories Inc Web page. These suggest that: AC-3 is a digital encoding technique that exploits "audio masking" to achieve high bit-rate reductions. AC-3 can be used to encode between 1 and 5.1 audio channels.

Both methods are what's known as lossy data compression schemes where some information that is masked by more prominent data is thrown away. This is done in order to fit a lot of data through a small data pipe. Dolby Digital (formerly called AC-3) takes 6 channels of 48kHz/24 bit information and compresses it at about an 11 to 1 ratio to an a maximum bit rate of 640kbps, although 384 is the average data rate used. DTS compresses at about a 3 to 1 ratio at an average data rate of 1.4Mbps.

Dolby Pro Logic takes its information from a two-track-stereo format. When a movie is recorded in Dolby surround, the Stereo soundtrack is recorded on the tape. Certain sounds (the surround-channel information) are encoded. Inside the Dolby Pro Logic receiver, the Pro Logic circuitry decodes the surround information and sends it to the rear channels. The center channel is derived by removing what is equal or nearly equal in the left and right channels and sending it to the center.

Yes, DVD-V200K does have a built-in decoder with Dolby Digital (Surround) (AC-3) processing; however, the output is only 2-channel stereo. No, from the modem day definition/understanding of a so-called built-in AC-3 decoder. Regardless, you can attach the DVD-V200K to a Dolby Digital-ready (i.e., 5.1-ready) A/V receiver/processor/amplifier to enjoy the benefits of 5.1 channel surround sound audio.

When using ADIF as transport syntax for the MPEG-2 AAC stream, "break-in" - i.e. start of decoding at any bitposition - is not possible because there is no sync word to synchronize with the beginning of the audio frames. When using ADTS as transport syntax, break-in is enabled. The complexity of break-in support depends on the profile. In MPEG-2 AAC Low Complexity and MPEG-2 AAC SSR modes, the prediction tools are not used, so break-in support is the same as that for MPEG-1 audio.

There is no public MPEG-2 AAC encoder reference source from MPEG. When purchasing the standard, you will get access to the MPEG reference software source for encoder and decoder. However, the encoder will not be optimized for quality or speed. To get state-of-the-art encoder source, you need to contact one of the companies which works on AAC.

Since many of the services based on MPEG-2 AAC are currently in their introductory phase into the market, numbers are changing constantly. Main areas of application are Portable playback devices A current estimation amounts to several million decoders (both software and hardware-based) and a lower number of encoders.

Yes, logos can be downloaded for the website at www.ncl.org and we strongly suggest utilizing the logo as much as possible.