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Dolby and DTS Surround Sound

I am sure all of you would have heard about Dolby and DTS at least in movies and DVDs. In this post, we will discuss these two most popular sound surround systems (Dolby and DTS) found in all media devices. Our discussion will be limited to widely used digital formats, its popular variations and future directions. Once you read the article, you will understand why DTS sounds better than Dolby in DVDs. I am not going to technical details of the formats and would be keeping the article simple. I assume that you have an AVR (Audio Video Receiver) capable of decoding all the formats discussed here.

DVD audio can be encoded as Dolby, DTS, PCM Audio or MPEG audio. Out of these PCM audio is uncompressed and others are compressed. Satellite DTH HD Channels comes with Dolby 5.1 or 7.1 sound encoding. Generally DTS is not supported by DTH providers. Blu-Ray comes with additional loss less formats Dolby True HD and DTS Master Audio offers the highest quality audio as the directors imagined.

Dolby Surround

Dolby Sound system was invented by Ray Dolby in 1965. It was an analog system for audio noise reduction. After many evolutions of Dolby analog systems like Dolby B and Dolby SR etc. Dolby digital was born in 1991. Our discussion will be limited to Digital systems. I like to mention that Ray Dolby has an Indian connection; he served India as UN technical advisor till 1965! May be he got this innovative idea in Indian soil.

Dolby Digital 5.1 (AC3)

Dolby Digital 5.1 is also known as AC3 sound (audio codec 3) is an advanced audio encoding/ decoding technology that efficiently delivers up to 5.1 discrete channels of surround sound for broadcasting, home theater, cinema, online streaming etc. 5.1 consists of three front channels (Left, Center, and Right) provide dialogue and accurate placement of on-screen sounds, while the Left and Right surround channels (rear speakers) immerse the audience in the action. The Low-Frequency Effects (LFE) channel delivers deep, powerful bass effects that can be felt as well as heard. Remember the thumbing footsteps of Dinosaur in Jurassic park movie. The LFE channel is referred to as a “.1” channel since it needs only about one-tenth the bandwidth of each of the other channels.

Speaker Placement

To reproduce all 5.1 channels you need 6 speakers as shown above. The placements of speakers are very important. The center Large Front speakers can reproduce most of the bass sound too but for best performance you need to set the crossover frequency between Front speakers and Subwoofer using a good calibration tool like Audyssey. It can be set in AVR (Audio Video Receiver) for <80Hz /<100Hz / <120Hz etc. depending on the frequency response of your front speakers. So Subwoofer will carry LFE + low frequency of other speakers. Subwoofer placement is not important since bass sound is not directional. But placing a subwoofer in a corner will enhance the bass at the risk of sounding boomy. Subwoofer comes in two formats down firing or front firing both can have different effects. Subwoofer can be active or passive (powered or non-powered) as can be 150W or 250W depending on your needs. Refer the following link to calculate the accurate placement of your speaker systems.

Center speaker is meant for reproducing most of the dialogues delivered by the on screen actors. So it should be placed in the same level as your ears, not much above or below. Dialogs from anybody not visible to the viewers will be directed to other speakers.

While reviewing this diagrams keep in your mind that “the goal of all speaker placement for movie soundtrack playback and multichannel music reproduction -- even stereo -- is a smooth, consistent and unbroken soundstage across the front, coupled with a sense of envelopment in the ambient surround effects” by Alan Lofft

Dolby Digital EX (6.1)

This is an extension of Dolby 5.1 systems and added a pseudo 6th central speaker at the rear. This is done by extending the capabilities of The Pro Logic matrix decoding technology. While it can rightfully be said this system is intended for a 6.1 playback layout but both Dolby and DTS refused to name it as 6.1 since the 6th channel is not a discrete one but generated from other channels.

Dolby Pro Logic II (Stereo Channels to 5.1)

This transforms stereo channels to surround sound.

Dolby Pro Logic II is an improvement on Dolby Pro Logic where 2 channel stereo music or movie sound is artificially reproduced to get the sound in all 5.1 speakers. So select Dolby Pro Logic II if you have stereo source (music or normal TV sound) but wants to have surround experience.

  1. Transforms ordinary stereo content into rich, full-range surround sound
  2. Ensures that you hear all the subtleties and detail of the original content
  3. Delivers seamless, natural surround sound

Dolby Digital Plus (HD-DVD)

Dolby Digital Plus extends the capabilities of Dolby Digital, providing a richer and more compelling audio experience. It provides up to 7.1 channels of surround sound with wide range of bit rates to ensure optimized sound quality for the available bandwidth. Two additional channels will be diverted to a pair of rear speakers which is placed behind the listener. It offers higher bitrates up to 6.144 Mbit/s, support for more audio channels and improved coding techniques to reduce compression artifacts. But this is not compatible with existing Dolby Digital decoders but the Digital Plus decoders can decode even AC3 sounds. It was adopted by HD DVD now a discontinued standard launched by Toshiba.

Dolby Pro Logic IIx 7.1 Channel enhanced surround sound (from stereo to 5.1 or 5.1 to 7.1)

You should select Dolby Pro Logic IIx if you have invested in 7.1 speaker systems. It is used for

  1. Delivering 7.1 channels from 5.1
  2. Stereo channels to 7.1
  3. 3 modes are there for giving optimum sound
    • Movie
    • Music
    • Game
In the music mode you have 3 options
  1. Dolby Center Width lets you control the balance of the main vocals in the center and front channels for more natural sound.
  2. Dolby Panorama creates a seamless, wraparound surround effect.
  3. Dolby Dimension lets you adjust for a deeper or shallower surround sound field depending on the size of your listening environment. It controls the more volume to front speakers or rear speakers.

Dolby Pro Logic IIz (Two height channels)

This is one of the most recent additions to Dolby. Conventional 5.1- and 7.1-channel surround sound systems deliver a horizontal sound field—sound is directed at you from only one vertical plane. Dolby® Pro Logic® IIz takes surround to the next level by adding front height channels—an additional pair of speakers positioned above the front left and right speaker creating a 7.1 or 9.1 playback systems for home music, movies, and video games.

In other words Dolby Pro Logic IIz brings enhanced spatial effects, added depth, and an overall airiness to the listening experience. It enables increased flexibility for expanding a 5.1 playback system to a 7.1, or a 7.1 system to a 9.1. As shown in the figure below two height channels can be added instead of the rear channels to make it 7.1 or add extra two height speakers to make it 9.1. One of the biggest advantages of this is that it makes the wiring simple if you have 7.1 speakers, move the rear speakers to front height J Or if you have enough money at your disposal and your spouse is ready to put up with the wires running across the living room, invest on two more speakers to make it 9.1 to get a full experience.

Dolby TrueHD

Blu-Ray Disc comes with Dolby TrueHD which is 100% lossless audio and is identical to the original master. It unleashes the ultimate high-definition audio experience and supports up to eight channels of 24-bit/96 kHz audio playback. It provides up to 4:1 compression efficiency, maximizing HD disc space and minimizing bandwidth requirements. Dolby TrueHD Digital out provides HDMI port to transport the lossless channels using HDMI 1.3 cables from Blu-Ray player to AVR where it is going to be decoded. It will not be available on both optical and coaxial cables. It provides eight full-range channels of 24-bit/96 kHz audio, and up to 5.1 channels of 24-bit/192 kHz audio.

I have included a table below which may guide you in selecting the listening mode in AVR for a given speaker layout and input source

Source Input5.1 Speaker Layout7.1 Speaker Layout9.1 Speaker LayoutModeCable
Stereo MusicDolby Pro IIDolby Pro IIxDolby Pro IIz MusicO/C/H
Stereo VideoDolby Pro IIDolby Pro IIxDolby Pro IIz MovieO/C/H
5.1 inputDolby Pro IIxDolby Pro IIz O/C/H
7.1 inputDolby Pro IIz O/C/H
Dolby TrueHDHDMI
*O: Optical C: Coaxial H: HDMI

Next, I will continue this discussion on surround sound systems with DTS Surround and the ways to tune your audio and video systems to get out of your audio and video gears.

Unlike Dolby, DTS is not a must for either DVD or Blu-ray. But DTS is more or less given as an alternative to Dolby in DVD and Blu-Rays and usually sounds better due to the less compression employed resulting in higher bit rate (24bit vs. 16bit) and the need for more storage size.

DTS made its first appearance in the Steven Spielberg movie Jurassic Park in 1993 just one year after the Dolby Digital which made its debut in Batman returns. DTS company (http://www.dts.com/) was found by Terry Beard (1990), funded by Universal City studios. As already mentioned Steven Spielberg introduced this technology to the common man in his movie Jurassic Park (1993).

Why DTS sounds better than Dolby in DVDs?

DVD standard calls for Dolby Digital 5.1 and it use 448kbps whereas DTS (which is not mandatory but often given with DVDs) uses a bit rate of 754.5kbps. You can compare this with the theoretical maximum bit rate of 640kbs (Dolby) vs. 1.5mbps (DTS) is seldom used in DVDs. The higher bit rate offered by DTS results in less distortion due to compression artifacts and is perceived as transparent by most listeners.

DTS Digital Surround (5.1 channels)

This is an alternative to Dolby Digital 5.1 and uses LC codec developed by Elisabeth Lochen and Pascal Chédeville in late 80s. This comes along with the DVDs for home DVDs unlike in movies where DTS sound comes in a separate CD. 5.1 speaker layouts is same as the one which I have discussed in the last article.

DTS –ES (6.1 Channels)

DTS extended Surround Channels add one more discrete central surround channel which can be played through a 7.1 speaker set. If the source is 6.1 but you have only 5.1 speakers systems the ES channel will be mixed equally to get a matrix audio through both rear surround speakers to create the illusion of a central speaker. So DTS-ES is backward compatible.

DTS – Neo 6 (stereo to 7.1)

DTS –Neo 6 is like Dolby Pro Logic IIx system which can convert stereo input to surround channel 5.1 or 6.1 channel format, in a 7.1 configuration, the two rear-center speakers play in mono.

DTS Neo X 3D sound (11.1 systems)

This is similar to Dolby Digital Pro Logic IIz which adds 2 separate height channels. DTS – Neo X is designed to complement the increased popularity of 3D video. In this the sound is more spaciously distributed. New height and width channel are added to surround you with immersing sound. Sound effects will be literally surrounds you taking you to new level of experience. This supports up to 11 speakers and the layout is given below.

DTS-HD Master Audio

DTS-HD Maser Audio is the loss less audio format available in Blu-Ray. This is the highest form of high definition Audio and allows a bit-to-bit representation of the original movie's studio master soundtrack. It uses up to 192 kHz sampling rate and can go up to 24bits depth of encoding resulting in a 24.5 mbps audio channels with support for 7.1 discrete channels.

This is backward compatible with 5.1 core. The data is sent in a single stream with separate core and extensions which makes it backward compatible with older DTS decoders.


Speaker Layout 7.1 Layout

Following picture shows the speaker layout for a typical 7.1 systems. If the room is large enough and wiring for the rear speakers is not a hassle you can adopt speaker layout 1.

Speaker Layout 1:

Speaker Layout 2:

If you have a limited space and want to escape from running too many long wires you can shift a pair of rear speakers to front and keep it as front left and right height speakers. This is an ideal solution to most of you.

How to connect DTS / Dolby Surround to AVR?

DTS / Dolby surround sound can be decoded to separate 5.1 /7.1 audio channels and directly connected to the surround speakers. The decoding can be done in DVD / Blu-ray or STB itself it has a built-in decoder but generally the decoding is done in a separate AVR (Audio Video Receiver). The player and AVR can be connected through HDMI / optical or coaxial cables. Please keep in mind that these digital audio signals are not available through RCA audio cables.

Case 1. New AVR with DTS-HD Master decoder

If you have an AVR capable of decoding DTS-HD always bypass the decoder in Blu-Ray player and use the option DTS-HD bit stream via HDMI 1.3 to inter connect both.

In other words use HDMI passes through so that the DTS audio decoding happens in your new AVR. This is the best form of connection.

Case 2. Old AVR without DTS-HD Master decoder

If your player is not supporting bit stream select multi-channel Linear PCM so that the decoding happens in your player rather than AVR. Remember that old FAT PS3 does not support bit stream over HDMI so you are forced to select multichannel LPCM whereas new slim supports bit stream.

Following table gives an over view of similar technologies from these competing standards.

Dolby DigitalDTS surround5.1 Channels
Dolby Surround EXDTS surround- ES6.1 Channels
Dolby Prologic IIxDTS Neo: 6Stereo to 7.1
Dolby Prologic IIzDTS Neo: X9.1 /11.1 channels
Dolby True HDDTS-HD MasterStudio Master Audio