Home theater audio is one of the more confusing aspects of the home theater experience. It's also one of the more satisfying when done right. TechDigs.net simplifies terminology, acronyms and standards to help you understand your best audio choice for music, DVD movies, and HDTV.

Read more for the details.

Home theater audio standards include numerous competitive and complementary technologies. Some of these technologies define specific standards related to how you hear audio, others define a quality level or seal of approval.

Depending on your level of experience, it will help if you start with the definitions that follow. If you just want to cut to the chase, then jump here.

Surround Sound Formats Summary
Least capable to most-capable (use the most capable format available in your system and content)

Definitions

Surround Sound: Surround sound is the generic concept of audio playback over two or more speakers to provide spatial imaging in two or three dimensions. Basically the sound "surrounds' you and simulates the experience of being right in the middle of a movie scene or listening to music in the actual concert hall where it was recorded. This is accomplished using numerous technologies. There are both analog and digital surround sound encoding methods. Surround sound is a key component in home theater audio systems.

Lossy audio compression: Lossy is an audio compression method where pieces of data are intentionally discarded to reduce the size of the data stream. Depending on the amount of compression, a lossy-compressed stream can be close enough to the original in accuracy and quality that the difference is insignificant. If the compression is higher, the lossy-compressed stream can sound quite different from the original.

Lossless audio compression: Lossless is a compression method where no pieces of data are discarded and therefore can reproduce bit-for-bit the originally recorded audio.

Matrixed audio decoding: Matrixed channel audio is audio that, when properly decoded, simulates more audio channels than actually exist in the audio files or streams. For example, decoding two-channel stereo audio using Dolby Prologic II can deliver five matrixed channels over your receiver. Generally matrixed audio is analog, although it can be digital as is the case of the rear center channels of Dolby Digital EX 7.1.

Discrete audio decoding: Discrete channel audio is audio that is encoded, transmitted, stored and played back as separate channels. Generally, multi-channel discrete audio is encoded digitally. An example of this is Dolby Digital 5.1. Discrete audio decoding is preferred over matrixed audio decoding.

Dolby Prologic (Matrixed Analog 4.1 Surround): Dolby Prologic is an analog matrixed surround sound standard created by Dolby Laboratories in the 1980s. It is 4.1 surround with Front-left, Front-center, Front-right, Surround-center, and subwoofer. Dolby Prologic was succeeded by Dolby Prologic II in 2000.

Dolby Prologic II (Matrixed Analog 5.1 Surround): Dolby Prologic II is an analog matrixed surround sound standard created by Dolby Laboratories in 2000. It is 5.1 surround with Front-left, Front-center, Front-right, Surround-left, Surround-right, and subwoofer channels. Prologic II can process both Dolby Prologic and stereo sound sources and simulate 5.1 surround pretty well. While the movie industry has clearly standardized on discrete digital encoding standards such as Dolby Digital and DTS, the music and video game industries still rely on Dolby Prologic II as a standard for surround. Dolby Prologic II has a movie mode, music mode, matrix mode and game mode. The music mode adds center and surround channels, but does not change the nature of the left and right channels. The movie mode is designed to provide a 5.1 experience for movies that are not digitally encoded. The game mode supports decoding for video games.

DTS NEO:6 (Matrixed Analog 5.1 Surround): Like Dolby Prologic II, DTS NEO:6 is an analog matrixed surround standard that can up-mix stereo content into a 5.1 or 6.1 surround format.

Dolby Digital (Discrete Digital 5.1 Surround): Dolby Digital is a family of digital surround encoding technologies from Dolby Laboratories. It is also known as AC-3 (Adaptive Transform Coder 3). It's capable of various channel configurations, however, it is most widely implemented as 5.1 surround. It includes Front-left, Front-center, Front-right, Surround-left, Surround-right, and subwoofer channels. Dolby Digital is a lossy encoding technology limited to 640 kbits per second, however, the DVD disc format limit it to 448 kbits per second. Since Dolby Digital treats each channel discretely and is digitally encoded, Dolby Digital requires a digital decoder to provide the 5.1 audio standard. Most home theater receivers can decode Dolby Digital, however, to get the signal from a source such as a DVD player to the receiver you must use a digital audio connection such as optical or coax.

DTS (Discrete Digital 5.1 Surround): DTS (Digital Theater Systems) is a competing standard to Dolby Digital. It's a discrete digital surround standard that offers multiple channel surround including Front-left, Front-center, Front-right, Surround-left, Surround-right, and subwoofer channels. Similar to Dolby Digital, it differs in one primary way. It offers lossy encoding up to 1536 kbits bandwidth on DVDs compared with Dolby Digital's 448 kbits. Depending on your sound system, you may notice a broader dynamic range and less hiss. Like Dolby Digital, DTS requires that your home theater receiver support decoding DTS and also requires digital audio connections (optical or coax).

Dolby Digital EX (Discrete Digital 6.1 and 7.1 Surround): Dolby Digital EX is an update to Dolby Digital which adds a matrixed Rear-center channel to a 5.1 setup. This can be accomplished through one (6.1) or two speakers (7.1). In 7.1, however, the two rear speakers operate as a mono channel.

DTS-ES (Discrete Digital 6.1 and 7.1 Surround): DTS-ES is Digital Theater Systems' competitive technology to Dolby Digital EX. Like Dolby Digital EX, DTS-ES builds on DTS and adds a center rear channel using one or two speakers. It differs from Dolby Digital EX in that the 6th Rear-center channel can be stored discretely in the source audio, as opposed to matrixed as it is in Dolby Digital EX.

Dolby Digital Plus (Discrete Digital 13.1 Surround): Dolby Digital Plus, also known as E-AC-3, is a new standard by Dolby Laboratories that provides beyond 8 channels. Current HD-DVD and Blu-ray implementations, however, limit it to 8 channels. Dolby Digital Plus increases the lossy encoding up to 6 Mbps. It is the required surround sound standard for HD-DVD and Blu-ray high def discs. It's also the future standard for ATSC HDTV broadcasts. Current digital audio connection standards (optical and coax) do not have the bandwidth to support Dolby Digital Plus. HDMI version 1.3 is the only currently supported connection methods for Dolby Digital Plus.

Dolby TrueHD (Discrete Digital 13.1 Surround): TrueHD is a very confusing name. It has nothing to do with high def video -- it's an audio standard. Confusing name aside, TrueHD is a next-generation lossless surround encoding standard. Supporting up to 24-bit/96 kHZ audio at up to 18 Mbits, it's a mandatory standard on HD-DVD and is optional on Blu-ray. It uses a HDMI 1.3 connection standard.

DTS-HD (Discrete Digital Surround, virtually unlimited channels): DTS-HD is Digital Theater Systems' answer to Dolby TrueHD. The specification allows for unlimited channels that can be down-mixed to the number of channels supported on the home system. The bit-rate is also flexible in that it can be as low as lossy DTS, or all the way up to lossless quality. DTS-HD is an optional standard on HD-DVD and Blu-ray high def discs.

THX: THX is a certification and standard created by Lucasfilm both for video content and for audio and video equipment. There are numerous THX certifications including: THX Ultra and THX Ultra2 (the THX standards for dedicated home-theater installations in a 3,000 cubic foot room); and THX Select and THX Select2 (the THX standards for non-dedicated and smaller 2,000 cubic foot home theaters). There has been much debate about the validity of THX certification and whether it provides measurable value in component and home theater design or do licensing fees just elevate pricing.

Now with all the definitions out of the way, here's the real-world impact.

Music
In a future TechDigs.net article, we will specifically address the various music formats and standards such CD, SACD, DVD-Audio and HDAD, and the related audio encoding standards. This article focuses only on recommendations for home theater audio. What surround standard you'll use in a home theater environment to listen to music will depend whether you are listening to music from CDs and digital music (MP3s, wav, AAC, FLAC, etc.), or from DVD-Audio. Since CDs and digital music generally include only stereo 2-channel audio, you should choose non-discrete surround encoding standards such as Dolby Prologic II or DTS NEO:6. For DVD-Audio, you'll generally want to use one of the discrete digital encoding standards such as Dolby Digital or DTS.

DVD Movies
For standard DVDs, a huge majority of the discs support Dolby Digital (AC-3). Many DVDs support DTS and other Dolby Digital variants (Dolby Digital EX and DTS-ES). Which audio option you choose when playing a DVD movie depends on your home theater system. You should choose the standard that sounds the best and optimizes your amplifier/speaker setup. For example, if you are setup for 7.1 audio, then choose DTS-ES or Dolby Digital EX. If in doubt, Dolby Digital 5.1 is a safe choice. Remember, to use a digital standard you must have the digital optical or coax connections to your receiver.

HDTV Broadcast and Cable
For broadcast HDTV, both Dolby Digital 5.1 and Dolby Prologic II are generally supported. However, which format you actually receive in the broadcast signal is determined by your local broadcaster and/or cable company. With certain channels and networks, we've found that even when programming says it's in Dolby Digital 5.1 it may not reach your system in digital 5.1. When that happens, setting your audio receiver/amplifier to Dolby Prologic II will likely provide the best results. Many receivers will revert to this setting if a Dolby Digital signal is not available. Keep in mind that just like DVDs, in order to use a digital standard you must have the digital optical or coax connections to your receiver from your cable or satellite set-top box.

High Def DVD Formats and the Future HDTV
For HD-DVD, Blu-ray and future ATSC HDTV, the standard are Dolby Digital Plus, Dolby TrueHD and DTS-HD. These standards will drive future audio systems. All of these devices also support today's Dolby Digital 5.1 standard.

So what format(s) should you use? That depends on your current system and the content you watch or listen to.

However, in order to enjoy the benefits of any of these formats you must have:

1. A compatible source device
   Your source devices such as DVD player, game console, set-top box, etc., must be compatible with, or at least allow pass-through of the encoded digital audio standard.
2. The right connections
   In order to pass digital standards such as Dolby Digital from your source, you must have the right connections between the device and your receiver - either digital coax or optical. For the new high bandwidth standards, you must have a compatible digital audio connection such as HDMI or IEEE-1394.
3. A compatible receiver or amplifier
   In order to decode the content from the source device, you must have an audio receiver or audio amplifier that is able to decode the audio standard you choose. For example, if you are watching a DVD with DTS audio content offered as an option, and your receiver supports Dolby Digital but doesn't support and decode DTS - don't choose DTS in the DVD menu system.
4. The right speaker setup
   Lastly, in order to get the benefit of 5.1, 6.1, 7.1 or more, you must have the right speaker setup. You should have at least 5 speakers (Front-left, Front-center, Front-right, Surround-left, and Surround-right) and a subwoofer connected to your audio receiver or amplifier.

Experiment with different content sources and settings on your DVD player and receiver so you better understand the differences. Most importantly, have fun with the realistic immersion that is home theater surround sound.

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David said:

A great article that finally explains the jargon with clear definitions and great advice. I now know what i'm looking for.

October 25, 2006

micromeathead said:

Here's a little more info on HDMI 1.3, the connector Dolby recommends for best results: HDMI 1.0 = video + L/R. HDMI 1.1 = 1.0 + DVD-A. HDMI 1.2 = 1.1 + SACD. HDMI 1.3 = 1.2 + Dolby TrueHD and DTS-HD

November 27, 2006

frank said:

many thanks for the needed lesson. keep up the good work.

December 22, 2006

Snipely said:

Since copper wire has no ability to differentiate between digital and analog data, can you please tell me what "digital coax" actually means? Is it a rated impedance to more exacting specifications (related to dimensional stability), loss per foot, frequency response, or shielding level that's important, and is there a published standard that can be refernced for performance miminums? I've seen both speakers and speaker cables labeled as "digital ready" which is a meaningless (marketing) term in that application.

March 08, 2007

TechDigs.net said:

Snipely: You are on track. The cable necessary to provide SPDIF (digital audio) over copper is no different than what would be needed to send an analog audio signal. Don't get caught up in the marketing hype and sweat the cable you use for a digital coax connection. If you hear audio, it's working fine. The key to our reference is that many people don't realize that the RCA jack on their DVD player is a digital connection that is identical in quality and capability to the optical Toslink connection.

March 08, 2007

gkoop said:

Thanks for the great article; I think I'm starting to get it. How does "Linear PCM" fit into all this? I have an LCD that I am using HDMI to feed. HDMI supplies both audio and video. However, the TV doesn't accept AC-3 or DTS (I suppose it lacks a built in decoder). In the manual it says "When the HDMI IN input is in use, surround sound, such as AC-3 and DTS cannot be input. Change the sound setting for the external input device to Linear PCM". I am happy to do it, but I wonder what it is. Is it just plain old stereo? Some sort of matrixed signal? It ends up having an impact on me because I have multiple monitors and it seems to force me to use a lower standard for audio than I would like. Thanks.

March 14, 2007

TechDigs.net said:

gkoop: In your description it's not clear what you are trying to achieve and what is providing the HDMI signal (DVD player, cable box, etc.). Let me see if I can describe the different options and maybe you can glean from that or ask another question or two. - If use the audio in your TV that was provided by plugging in HDMI, it'll probably be stereo with any analog encoding that may be possible (Dolby Pro-Logic II). - If you plug HDMI into a home theater receiver, then it'll process a 5.1, 6.1 or possibly 7.1 depending on the source material and the receiver. That assumes your HDMI is newer. If not, it could be stereo. If you let us know what devices you have, we can probably provide some help and advice. - If you plug HDMI into the set and then plug optical audio or coax digital audio (RCA plug) into a home theater receiver, it'll either be 5.1 audio or 6.1 audio depending on the receiver and the source material.

March 15, 2007

Sean McGuire said:

Brilliant article. One Specific query for my setup. I have a Yamaha amp which has a surround enhanced setting-do you know if this compliments the audio types above and therefore "enhance" the audio experience (as the name would suggest) or does this replace it with a particular type of Yamaha coding in which case is it a better setting to have. Regards Sean.

April 07, 2007

TechDigs.net said:

Sean McGuire: Thanks! Depending on the source material, on most systems a surround enhance is a DSP function to enhance 2 channel material to make it simulate various surround sound situations over all 5/6/7 speakers. For example, it might simulate a concert hall or a jazz club. This can be a decent effect for some music - purists don't like it. On the Yamaha's (like the RX-V750), Yamaha uses the DSP to 'enhance' 5.1 digital material. Some don't think too highly of it because it generally makes effects echo-ie (not the center channel, but the others). Because digital surround material is already setup to sound appropriate for the effect, it can't really add value and may even detract. In our opinion it's like putting your home theater in an old gymnasium with hard walls - making sounds go from tight to sloppy. We're not fans. Our recommendation is to leave it off, but to each his/her own.

April 07, 2007

Morgan said:

It seems pretty much every DVD I run across has 1 sound option; Dolby Digital 5.1. Few DTS, and no "higher end" choices, Dolby Digital-EX ,DTS-ES etc. I spent the $$$ on the equipment but I feel like i'm only using 50% of it's capability...now where is all the content?? Is there a list of the movies somewhere that DO have "higher end" audio?? choices??

September 13, 2007

walterk1 said:

I am planning a new home/HT setup. I want to run cables from flat panel above fireplace to rack nearby - in the walls. I am trying to figure what I need to run in the walls. I have HDMI port on TV (sony kdlS2010), along with a bunch of component/S-video, analog audio, and toslink/dig coax. I do not have the receiver yet. I am trying to figure if I can use the TV as center channel, and what I need to run from Rec to TV. I am guessing HDMI for vid/aud from Receiver that gets HDMI from Cable box. Do I need to use the dig aud out from TV back to the unit? Or somehow make the TV the center from the receiver.

September 18, 2007

Ryan said:

Can a 7.1 system be set-up as a 5.1 system? I only have ability to set up a 5 speaker system (room layout) but like the componenets of the onkyo HT-SR800 that is 7.1. Could I just not hook up the two rear channels, or should I leave out the 2 rear surround channels instead?

March 04, 2008

Jody said:

I have a beautifuy Blu Ray player and an Onkyo 805. I noticed that on Blu Ray whether its DTS-HD or DOlby TrueHD the back surrounds do not engage- while if I use a standard DVD with Dolby 5.1 or DTS the rear surrounds do work. What gives??

March 06, 2008

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