Dolby Plus, Dolby TrueHD, DTS-HD and DTS-HD Master Audio: Next Generation Audio

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These are exciting times for home theatre enthusiasts. The goal of replicating the movie theatre experience in our own homes is becoming increasingly possible.

Unfortunately competing standards and formats are making it difficult for consumers to appreciate, understand and accept the latest technology. The heavy weight battle is between Plasma and LCD flat panel displays. Blu-ray and HD DVD are duking it out in the high definition video category, HDMI is in the ring without an opponent but seems to be beating itself up with compatibility issues and finally we have the long standing battle between Dolby and DTS, which will be the focus of this article.

Dolby Digital and DTS are the multi-channel surround formats of the familiar standard definition DVD. Initially Dolby Digital was adopted as the standard for DVD and is the more commonly included surround format on DVDs. Not long after, DTS was included in the official DVD specification and, although optional, an increasing number of DVDs were released with an optional DTS soundtrack that many argue sounds better than Dolby Digital. In theory DTS is capable of 1.5 Megabits/second (Mbps), while Dolby Digital tops out at 640 Kilobits/second (Kbps). In practice the soundtracks on DVDs are encoded at 448 Kbps for Dolby Digital and 754 Kbps for DTS. The vast majority of DVDs are released with 5.1 channels of audio.

The most common method of connecting a DVD player to a receiver is by using an optical or coaxial digital cable. Another more recent solution is the HDMI cable. This single cable carries both the video and audio information.

DTS Encore Audio is also referred to as the DTS “core” track. This is a 1.5 Mbps track that has been available in theory to standard DVDs. The beauty of this codec is that all current receivers that decode DTS can decode the core track via the digital optical or coaxial connection of a Blu-ray or HD DVD player.

Dolby Digital Plus is a step up from Dolby Digital. It is mandatory for HD DVD players to decode Dolby Digital Plus. Bit rate jumps from 448 Kbps to a maximum of 3 Mbps and goes from 5.1 to 7.1 channels of audio. In the Blu-ray format this codec is optional. Although it will still deliver 7.1 channels of sound, the bit rate is capped at 1.7 Mbps. Dolby Digital Plus is a more efficient codec than standard Dolby Digital and in theory it can deliver up to 18 channels of audio or 6 Mbps of data.

DTS HD High Resolution Audio is a step up from DTS Encore. This codec allows for 8 full range audio channels at a maximum bit rate of 6 Mbps on Blu-ray or 3 Mbps on HD DVD.

Dolby Digital True HD is another mandatory format that all HD DVD players must support, but optional for Blu-Ray. Up until this point, all of the mentioned codecs have been lossy. But True HD is lossless, meaning that for the first time ever in your own home, you can potentially hear the soundtrack exactly as it was mastered for the theatrical release of a movie. And I say “potentially” because those little cube speakers that many people use in their audio setup are just not going to give you a true “True HD” experience. This codec is based on the MLP lossless format developed for DVD-Audio. True HD supports 8 full range audio channels and operates at a maximum bit rate of a whopping 18 Mbps in both Blu-ray and HD DVD

DTS HD Master Audio is the DTS answer to lossless encoding. This format is also capable of delivering the studio mastered soundtrack in your home theatre. DTS HD MA, as you will come to know it, supports 8 full range channels of audio and operates at a maximum of 18 Mbps on HD DVD and up to 24.5 Mbps on Blu-ray.

Linear PCM is the wild card. LPCM is the uncompressed sound format that we are used to enjoying on a standard CD. The benefit of this format is high resolution audio without the cost of licensing fees to Dolby or DTS for using their advanced codecs. Some studios have used this route in their Blu-ray releases. They can get away with this because of the large storage capacity of Blu-ray which allows for the inclusion of these uncompressed soundtracks. This can’t possibly last very long as consumers will demand more bonus features and additional sound tracks and the studios will have to bite the bullet and start paying Dolby or DTS or both to use their more efficient encoding.

These four new surround sound formats (plus the wild card LPCM) have added a layer of complexity to the Blu-ray vs HD DVD format war that will leave more than a few people scratching their heads.

The good news is that no matter which high definition format you choose to support you will still be able to, at the very least, listen to the movie’s sound track in good ol’ Dolby Digital. In fact using the most basic digital connection (optical or coaxial) will result in a slight improvement over standard DVD. As mentioned earlier the core DTS track can be decoded at 1.5 Mbps which is double the rate currently available on DVD. And Dolby Digital goes up slightly to 640 Kbps on Blu-ray, but stays the same (448 Kpbs) on HDDVD.

From there it gets a bit more complicated. There are currently no A/V receivers that decode any of the new sound formats. This means that the decoding must be done on board by the HD DVD or Blu-ray player.

If your receiver is equipped with an HDMI input then the higher resolution formats will be decoded by the player and passed to your receiver as LPCM. The Digital to Analogue Converters (DACs) in your receiver will then take over.

You may recently have paid good money for a very good receiver with very good DACs, but it may not have an HDMI input. If this is the case and you don’t plan on upgrading the receiver in the near future, then you’d do well to get your self a player with multi-channel RCA analog outputs. In this scenario the player will do the decoding of the new formats and the digital to analogue conversion with its on board DACs. The signal will then pass to your receiver through the RCA connection. This method will work very well as long as your receiver has bass management for the analogue inputs

Down the line we will start to see the release of A/V receivers with HDMI 1.3 connections and built in decoding for the new surround formats. Currently the only Blu-ray player with an HDMI 1.3 output is the Sony PS3 but next generation stand alone Blu-ray and HD DVD players will include HDMI 1.3 outputs. This will provided the simplest solution to high resolution audio. The encoded bit-stream will be sent to the receiver for decoding and digital to analogue conversion. Not only will this result in a simple one cable connection solution but the players themselves will come down in price as they won’t need to incorporate bit-stream decoding and DACs.

In theory things are looking and sounding great. In practice things are a little messy right now but the future looks bright for the home theatre.

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