The Basics of Home Theater:
Terms and Technology
Last updated 6/9/2006
TERMS AND TECHNOLOGY
How often have you heard jokes about people's VCR clocks flashing "12:00" because they can't figure out how to set the time? Well, get ready, because the VCR is child's play compared to the complexity that you can encounter when setting up and using a home theater system. To get the ball rolling, I've gathered some common terms and bits of technological info that can come in handy for anyone venturing into the world of home theater. Most of this will come up again later in the guide. We'll start with some common terms, but there are also some sections looking specifically at surround sound processing, video, and cabling. I'll probably add to this page regularly as I see folks asking questions online and as terms occur to me.
Surround Processing Modes:
- Reference Level: This refers to a standard sound level used for calibrating the individual speakers in a surround system so that they all produce the same sound power level at the system's listening position. This is not the level at which you are supposed to listen to the system in fact, it's probably at least 10dB higher than most people will want to listen. What it is is a known and reproducible volume level that sound engineers can use as a baseline for mixing movies.
- Decibel/dB: The "bel" is a unit of measure for sound power level named for Alexander Graham Bell. In general use, we use the unit of measure "decibel" (or one-tenth of a bel, appreviated as "dB") for measuring sound power levels. It is a logarithmic unit of measure, not a linear one. What this means in general terms is that adding 10dB doubles the loudness. Also of interest in home theater applications is the power needed to generate a louder signal doubling the power input will yield a 3dB increase in loudness. For some idea of what difference a change in decibel level can make, here's a common description:
- 1dB: Imperceptible Change
- 3dB: Barely Perceptible Change
- 5dB: Clearly Noticeable Change
- 10dB: About Twice as Loud
- 20dB: About Four Times as Loud
- Transcoding: This refers to a process by which a video signal of one type is transferred to a different type. For example, a composite video input to a receiver from a VCR might be transcoded to component video and output from the receiver to the TV. This is useful for simplifying the number of video cables needed between a receiver and a television.
- Anamorphic: Anamorphic is a term first seen in relation to DVD. The Digital Bits has an excellent article explaining what anamorphic video is. Basically, anamorphic encoding stores a 16:9 widescreen image on a regular "square" (4:3) frame in order to make maximum use of the available lines of resolution. When the video is to be displayed on a 4:3 display, the player "squeezes" the video and adds black bars at the top and bottom so that the original aspect ratio is displayed properly.
- Ground Loop: A condition in which differences in the electrical path to ground create a hum in an audio signal (or noise and interference in video signals, although audio hums are most often cited as indicators of the problem). If you think you have a ground loop, check the Receivers section (under Amplification) for further discussion of the issue.
- Monitor Output: This is a video output on a receiver or video processor that is specifically intended for connection to a "monitor" the television, normally.
We'll get into this again when we talk about receivers, but one area that will inevitably come up and will inevitably lead to confusion is the subject of surround processing modes. Once upon a time, there was just Dolby Pro Logic if you had a "HiFi" VCR (which was the term used for a VCR with a stereo audio output), you could use a Pro Logic receiver to enjoy surround sound. Times have changed, however: the LaserDisc provided the first means of delivering true discrete surround sound to people's homes (the method was Dolby's "AC-3" which we now know by the friendlier name Dolby Digital), and DVD helped bring about something of a revolution in surround sound. The list below offers an introduction to the most common players in the surround sound game, including several that aren't going to be available on most receivers but will potentially come up in discussions.
Video in the HD Age
- Dolby Pro Logic: This is an older surround processing that was based on a stereo analog signal into which a center channel and a surround channel (mono, with both left and right surrounds getting the same signal) were "matrixed" into the left and right channels so that a Pro Logic decoder could extract them. When given a true stereo signal (i.e. a signal that was not originally intended for Pro Logic decoding), the Pro Logic decoders often had a hard time getting much out of the signal it would sometimes collapse entirely to the center channel, for example. Today, Pro Logic is essentially dead, replaced by its successor Pro Logic II.
- Dolby Pro Logic II: Pro Logic II is a new form of decoding intended to work with a stereo signal. It can still handle Pro Logic soundtracks, but it can also work well with purely stereo soundtracks. In many cases, Pro Logic II decoders include up to three modes -- one for movies, one for music, and sometimes a third for games. Also, unlike the original Pro Logic, PLII produces a five channel output (discrete left and right surrounds in addition to the mains and center) and a full-range signal to all five channels (Pro Logic's surround signals did not cover the full 20Hz-20,000Hz frequency range, being limited instead to 100Hz-7,000Hz; the mains and center were full-range). Basically, Pro Logic II gets closer to the sound of Dolby Digital soundtracks than Pro Logic did. Pro Logic II is intended mainly to enhance the listening experience with analog stereo signals such as video tapes, cable and satellite TV, LaserDiscs with two-channel audio, and video games (the GameCube, for example, does not support Dolby Digital, but many games come with soundtracks specifically mixed for Pro Logic II). For more information , you might be interested in this link to Dolby's site.
- Dolby Pro Logic IIx: Pro Logic IIx first appeared in 2003, and as of 2004 began to appear in receivers and SSP's. It is obviously based on Pro Logic II, but adds two things: seven channels (it adds stereo surround back channels to Pro Logic II's five full range channels), and the ability to be paired with a discrete 5.1 signal to generate stereo surround back channels. Secrets of Home Theater and High Fidelity published a summary of Pro Logic IIx and its relation to the other decoding schemes available in this article in March 2004.
- Dolby Digital: Dolby Digital is very different from the two Pro Logic formats. It is a digital format, with five discrete full-range channels (left, right, center, left surround, and right surround) and a ".1" low frequency effects ("LFE") channel. Dolby Digital is the standard audio format for DVD video. While the "standard" Dolby Digital track is a full 5.1 track, it is possible (and common, especially on DVD's of older movies that were originally mixed in mono or stereo only) to have Dolby Digital tracks that only include some of the 5.1 tracks. Dolby Digital 2.0, for example, would be a stereo mix with left and right channels only (many old Pro Logic soundtracks have been transferred to DVD in this manner, and still retain the old Pro Logic steering). Dolby Digital 4.0 would have left, right, center, and a mono surround channel (which might be a direct conversion of an older Pro Logic soundtrack). Dolby Digital 5.0 would have everything except a LFE track for the subwoofer.
- Dolby Digital EX: Dolby Digital EX is an extension of Dolby Digital that adds a surround back channel (one or two speakers at the back of the room) that is matrixed into the surrounds, much the way the Pro Logic matrixed in the center and surround channels. It was originally used in theaters for Star Wars: Episode I in 1999, but Dolby began licensing it for use in consumer electronics around late 2001.
- DTS: DTS is the same (in concept) as Dolby Digital five full-range and one LFE channel in a digital format. DTS is not as heavily compressed as Dolby Digital, though, which many people believe allows it to sound better. It was originally developed for use in theaters, but its creators extended it to consumer electronics and at one point tried to make it the standard audio format for DVD's. Dolby Digital won that battle, but DTS was included in the DVD specifications. You can find more out about DTS in home theater here.
- DTS-ES: DTS-ES is very similar to Dolby Digital EX. It is an extension of DTS that includes a surround back channel. A few DTS-ES soundtracks can be found on DVD's. On these tracks, the surround back channel is a discrete signal (rather than having it matrixed into the left and right surrounds as is done with Dolby EX). Early on, DTS-ES also referred to a mode that allowed matrix decoding of DTS 5.1 tracks to generate a surround back channel; these days, DTS has changed their decoder structure a bit and passed this duty on to NEO:6 since they were using the NEO:6 processes for this work anyway.
- DTS NEO:6: NEO:6 is DTS's version of Pro Logic II. It is a matrix decoding scheme that produces 5.1-channel surround sound from a stereo input. NEO:6 can also be applied to DTS 5.1 soundtracks to create a mono surround back signal, much like using EX or PLIIx processing with a Dolby 5.1 soundtrack.
- THX: THX dates back to the 80's, when George Lucas was so disappointed in the quality of the audio and video systems in most theaters that he created the company to provide "quality control" for theaters. Eventually, that extended to home theater. THX home theater certification extends to almost every component in the system (receivers, amplifiers, speakers, etc.), but there is also a THX decoding system that many receivers and pre/pros use. THX processing is similar to Dolby Digital processing (THX processing can be used for Dolby Digital soundtracks but not DTS soundtracks), but includes some other processing requirements. In some regards, it is an extension of Dolby Digital processing. For more on the home THX program, try this page or this Secrets article.
- THX Surround EX: Several years before Dolby began licensing Dolby Digital EX for use in consumer electronics, THX began licensing THX Surround EX for home theater. THX EX uses the same basic matrix decoding that Dolby EX uses to produce a surround back signal.
- Logic7: There are a number of proprietary processing systems on the market, but the most widely known is Logic7. Logic7 was developed originally by Lexicon and offered on their surround processors in various forms dating back to the DC-1 and DC-2 in the late 1990's. It is capable of producing a 7.1 output (including separate left and right surround back channels) from any source, and fans of Logic7 consider it to be one of the most effective matrix decoding schemes around for both movies and music. When Harman International bought Lexicon, they began offering Logic7 processing on their Harman/Kardon receivers.
- Dolby Digital Plus: Dolby's scheme for an audio format to accompany newer HD video formats, primarily Blu-Ray and HD-DVD although it has also been approved by ATSC (Advanced Television Systems Committee) for use in the limited bandwidth realm of HDTV broadcasting. The basic concept allows for a significant number of discrete channels (13.1 is the theoretical max for the format), but it will initially be treated as a 7.1 discrete format. There is a good general FAQ available from Dolby Labs in PDF format. The big question currently looming over the industry is how DD Plus signals will be carried between source components and receivers or surround processors. The coaxial and optical digital cables that have become so prevalent can't handle the format. IEEE-1394 (FireWire or i.Link) is capable of carrying the data but is not approved for the format in fact, until HDMI v1.3 is released some time in late 2006 there will be no approved means of passing a DD Plus digital bitstream. The only approved means of passing a DD Plus soundtrack is to decode it to multichannel PCM in the player and to pass that data over HDMI v1.x or to convert that PCM to analog and send it out through a 7.1 analog output. Until HDMI v1.3 arrives, receivers will not be equipped with the hardware and software needed to decode DD Plus. Due to the huge installed base of Dolby Digital/DTS receivers, it seems very likely that most Blu-Ray and HD-DVD players will include the necessary onboard decoders along with a set of 7.1 channel analog audio outputs that will be compatible with existing receivers' multichannel analog inputs.
- Dolby TrueHD: Dolby TrueHD is a successor of sorts to DVD-Audio. It uses Meridian Lossless Packeting (MLP) to store digital audio with lossless compression. The same output restrictions that make Dolby Digital Plus so cumbersome apply here as well.
- DTS-HD: DTS has consistently answered each of Dolby's digital formats with one of their own. In the case of DD Plus, DTS responded with DTS-HD. Like DD Plus, DTS-HD is going to support 7.1 channels, will be included on both Blu-Ray and HD-DVD, and will offer backward-compatibility (so a DTS 5.1 signal can be passed through a coaxial or optical digital output). Also like DD Plus, it will require a different digital audio connection to pass it to a receiver (the upcoming HDMI v1.3) or probably a 7.1 analog connection. Borrowing a page from Dolby TrueHD, DTS-HD will also offer an option for lossless audio compression.
There are a number of confusing terms and abbreviations that can be found when looking at televisions and video sources today. The terms below may not cover everything, but they'll be a good start at least.
The Long and Short of Cabling:
- SDTV: Standard Definition TV. This term is routinely used now to describe a standard non-digital, non-high definition television.
- DTV: Digital Television. This refers to any TV that can accept a digital video input. The federal government will be shutting down analog over-the-air television broadcasts on February 18, 2009, after which time all TV's will need to be digital or have a digital converter box to accept over-the-air television broadcasts. Note that a DTV is not necessarily high-definition.
- EDTV: Enhanced Definition Television. This refers to a digital television that will accepting and displaying a 480p signal. An EDTV is not truly high definition.
- HDTV: High Definition Television. This refers to a digital television that is capable of displaying a high definition signal at least 720p, but also 1080i or 1080p.
- Aspect Ratio: The shape of an image is its aspect ratio. This is usually described in terms of width versus height, either in whole numbers (16 units across for every 9 units high, or 16:9) or as the number of units of width per unit of height (1.78 units across for every unit of height). Below are the most common aspect ratios.
- 16:9 The standard aspect ratio for anamorphic video on DVD and for HDTV video content
- 4:3 The traditional aspect ratio for standard definition television, taken from the original movie aspect ratio.
- 1.66:1 An aspect ratio developed for some widescreen movies, commonly used in Europe but rarely seen in the US.
- 1.78:1 Identical to 16:9.
- 1.85:1 One of two common theatrical widescreen aspect ratios, typically referred to as the Academy Flat aspect ratio.
- 2.35:1 A second common theatrical widescreen aspect ratio, typically associated with the "Scope" format (Cinemascope or Panavision).
- Interlaced: Interlacing is an old trick for redrawing a high-resolution picture without having to refresh the entire picture each cycle. In the US, our electrical grid operates at 60Hz, so that's the "clock" that many things cycle at, including the picture on your TV screen. Interlacing means that each 1/60th of a second, the TV will update half of the lines on the screen. The following 1/60th of a second, the other half will be updated. The interlaced process refreshes odd numbered lines during one cycle and even numbered lines during the next. This way, the entire picture is redrawn every 1/30th of a second, giving us 30 frames per second. This is actually slightly better than the film projection used in theaters, which runs at 24 frames per second.
- Progressive: Progressive scan describes a refresh process that redraws all of a screen's lines at once during each cycle. This gives you the equivalent of 60 frames per second, which means you can get a crisper and more life-like picture.
- 480i: 480 lines, interlaced. This is the resolution used by most standard definition television. It is also the native video resolution for DVD.
- 480p: 480 lines, progressive scan. This is the resolution most often associated with EDTV. Beginning around 2000 or 2001, some DVD players began offering progressive scan output, which referred to a separate processing layer that "de-interlaced" the signal and produced a 480p output. Conventional SDTV's couldn't use this progressive scan signal, but EDTV's and HDTV's could. We're still not to HD resolution yet, though.
- 720p: 720 lines, progressive scan. Now we are at HD resolution. 720p is the threshold for HDTV. Until late 2005 or early 2006, nearly all LCD and DLP rear-projection TV's used chips that had a native resolution of 768 lines and could project a progressive scan picture. This allowed them to (just barely) achieve a native resolution at or above the 720p threshold. There are now some DLP systems that can achieve a resolution of 1024 lines, putting them very close to our next entry.
- 1080i: 1080 lines, interlaced. Until 2005 saw a few displays that operated at 1080p, this was the highest resolution available for a consumer display. Many direct-view CRT HDTV's had a native resolution at or near 1080i, although direct-view CRT is disappearing from the HD market due to its cabinet depth and weight.
- 1080p: 1080 lines, progressive. As I mentioned a moment ago, there started to be displays that claimed 1080p resolution by early 2005, but in general those displays could not accept an 1080p input the best they could do was to de-interlace a 1080i input. This was at least partly due to the fact that no 1080p source material existed at the time. The arrival of HD-DVD and Blu-ray in 2006 changed that: both formats support 1080p resolution and many discs contain 1080p video. Toshiba's first generation of HD-DVD players were limited to 1080i output, however, leaving the early Samsung and Sony Blu-ray players as the only true 1080p sources available to consumers.
- HDCP: High Definition Copy Protection. This copy protection encryption/communication protocol is used with DVI and HDMI connections to insure that the source component, display, and any intermediate devices preserve the integrity and security of the data. It is a tool used to prevent piracy of digital video signals.
For serious questions about cabling, check out the Cables and Sample Wiring Diagrams sections. For a quick glimpse of the subject, check out the few terms below.
- Analog Audio: Until the 1990's, almost all audio signals between components traveled in the analog domain.
- Stereo Two cables (often fused together) carry two separate analog signals, one for the left and one for the right.
- Multichannel Six or even eight cables carry separate analog signals for multichannel surround data in the analog domain. That spaghetti of cables is a significant reason for people's preference for digital audio connections.
- Digital Audio: The first opportunity that the average consumer had to pass digital audio came with the Audio CD. Some higher-end stereo systems started to use separate CD transports and outboard digital/audio converters, with a digital audio connection between the two. The arrival of DVD and HDTV has helped trigger the migration from analog audio to digital audio connections between gear.
- S/PDIF S/PDIF is the Sony/Philips Digital Interface Format, a specification for transferring digital audio data between devices. S/PDIF can be used over a number of different connections, including RCA or BNC connectors (typically called "coaxial"), AES/BEU (the same connector used for balanced analog audio), and TOSLINK optical.
- Coaxial An S/PDIF digital audio cable that uses an RCA connector.
- Optical An S/PDIF digital audio cable (often called TOSLINK, the name originally given to my by Toshiba) that carries the same data as a coaxial digital cable. Instead of the signal traveling over copper, however, it is converted to optical and passed over a plastic or glass fiber optic cable.
- IEEE-1394 / FireWire / iLink The FireWire interface was developed for the computer industry as a high-bandwidth competitor to USB. It has seen very limited use as a digital audio connection for DVD-Audio and SACD, but the underwhelming performance of those two formats has led to very limited adoption of FireWire on equipment.
- HDMI This "all in one" digital audio and video connection is new and is in fact still undergoing revisions. The latest version as of this writing (v1.2) supports digital bitstreams for everything that coaxial and optical digital cables will carry plus DVD-Audio and SACD. It also supports up to eight channels of PCM data, allowing it to carry decoded digital output from Dolby Digital Plus, DTS-HD, and Dolby TrueHD sources. The next version (v1.3) will support bitstreams for those three formats, allowing the decoding to move to the receiver. Hardware support for HDMI audio remains very spotty. For more details on HDMI, check out my HDMI FAQ.
- Speaker Cables: Speaker cables get an amplified analog audio signal, which is carried by two conductors (one positive and one negative). It's important to get the polarity correct for optimal sound quality.
- Analog Video: Until HD arrived, all video traveled in the analog domain. As a result, we've developed a number of different analog video connections over the decades.
- RF This is actually a combination audio and video connection on a single conductor that basically mimics the TV station's analog broadcast. Use it only if you have no other option.
- Composite Carrying the analog video in a single signal is a step up from RF, but that's about all that can be said for composite. Use it for your VCR, but for anything else upgrade if your TV will let you.
- S-video Consumers first saw s-video when Super-VHS VCR's arrived in the late 1980's. My dad still has his old S-VHS camcorder, and I've got an S-VHS VCR for that reason. S-video divides the signal into two pieces (brightness and color), which improves the overall quality of the signal.
- Component This is where analog video peaked. Component video connections can carry up to a 1080i signal, and as a result it was the only connection to use for HD video until digital video arrived.
- VGA Your old CRT computer monitor is an analog display device, which is why your monitor cable is carrying an analog video signal over its VGA cable. We see VGA connections occasionally on TV's, but mainly front projectors that can then be marketed both to home theater enthusiasts and to businesses for use with a laptop computer and PowerPoint presentations.
- Digital Video: HDTV is based on a digital video signal and many of the newest display devices are digital, so it makes sense to preserve the digital signal path all the way from source to display. That's where these connections come in.
- DVI Originally developed for use with flat panel LCD computer monitors (which are digital display devices), DVI was borrowed by the consumer electronics industry for use with HDTV. They did add HDCP for copy protection, but otherwise nothing was changed. That's why the DVI connector looks so much like your old VGA connector.
- HDMI When a group of manufacturers got together to come up with a way to pass all this new digital data back and forth, the result was HDMI. It lifted the digital video signal structure directly from DVI (including the HDCP copy protection), which means that DVI and HDMI devices can be connected without anything more than an adapter or a cable terminated with one of each connector. HDMI also added audio, which DVI of course lacks. The HDMI group came up with a much smaller connector that looks more like a USB connector (or perhaps the iPod connector) than anything consumer electronics users are used to. That connector may get revised in a future revision because of problems with the connectors pulling out from the weight of the cable. For more details on HDMI, check out my HDMI FAQ.
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