5.1-channel, 6.1-channel, and 7.1-channel inputs
A receiver's 5.1-channel input features preamp-level jacks for 6 channels: left main, right main, center channel, left surround, right surround, and subwoofer (sometimes called "LFE" or "Low-Frequency Effects"). Because the LFE channel carries a limited range of very low frequencies, it's the ".1" in 5.1.

A 5.1-channel input allows you to hook up a separate multichannel surround sound (Dolby? Digital, DTS?) decoder, such as those built into some DVD players. You can also use these inputs with multichannel music sources like DVD-Audio and SACD players.

Some receivers feature a 6.1 or 7.1-channel input. These let you hook up any of the 5.1 sources described above, but also pave the way for future upgradability. One potential use for these inputs is hooking up decoders for surround formats that offer 6.1 channels, such as Dolby™ Digital EX, DTS-ES™ and THX Surround EX™.

Audio/Video inputs and outputs
An Audio/Video input consists of three RCA jacks — two for the stereo audio signal, and one composite video input. Some A/V inputs also include an S-video input. Typically, if you've made connections to both the composite and S-video inputs of a single A/V input on a receiver, precedence will be given to the signal coming in via the S-video input.

Receivers with A/V inputs and outputs offer convenient remote switching for your A/V sources.

Automatic speaker calibration
Receivers with this feature can analyze and automatically adjust the sound of connected loudspeakers. A model with this capability sends a series of test signals to each speaker in your surround sound system, then measures the response with an included calibration microphone to optimize the speakers' volume level, time delay settings, and frequency response — making speaker setup easier and usually more accurate than manual methods.

Component video inputs and outputs
A single component video input includes three RCA jacks — one for the brightness (luminance) portion of the video signal, and two for the color (chrominance) portion. Because component video connections split chrominance between two jacks/cables, they offer even higher-quality video transfer than S-video connections, with improved color accuracy and less bleeding.

Receivers with component video switching allow you to select between multiple component video sources. However, just because a receiver offers component video switching doesn't mean it can pass on all video signals flawlessly. Component video bandwidth is the key figure to look for here. You'll need bandwidth over 10 MHz to pass on progressive-scan video without noticeable softening of the picture. And for HDTV signals, you'll need bandwidth of 28MHz or more to avoid noticeable softening of the picture (with most TVs). All new home theater receivers offer HDTV-capable component video switching, but a number of older models do not.

Component video conversion
A select number of home theater receivers offer this very flexible form of video conversion. It enables your receiver to take incoming video signals from composite, S-video, or component video connections and pass them to your TV through one component video connection. As with composite-to-S-video conversion (below), component video conversion offers multiple advantages in the convenience department, but does not improve the picture quality of your video sources.

Composite-to-S-video conversion
Home theater receivers with this feature can send video signals received via any composite or S-video input to your TV through a single S-video connection. This is especially handy if your TV has a limited number of video inputs. Composite-to-S-video conversion not only simplifies hookup, but can also reduce or eliminate the need to switch source inputs on your TV. Note that there is no improvement in picture quality to video signals input through composite video connections — the advantage of this conversion is solely a matter of convenience.

Composite video inputs and outputs
A composite video input or output uses a single standard RCA-style jack to pass video signals. This type of connection combines chrominance and luminance information, sending it along a single cable. Though capable of delivering a fairly high-quality picture, composite video is not as accurate as either S-video or component video, both of which provide separate paths for chrominance and luminance.

Digital audio inputs and outputs
A home theater receiver's optical or coaxial digital inputs accept Dolby Digital and DTS signals from digital home theater sources (such as DVD and DBS). They also accept PCM stereo audio from components with compatible output (such as CD players). Digital inputs on stereo receivers are designed for the latter use only.

A digital output lets a receiver send PCM stereo digital audio directly to digital recorders (such as CD-R). Optical digital outputs are the type most commonly found on receivers, but some models offer coaxial outputs, too.

Optical digital connections require a special type of fiber optic cable, usually with Toslink connectors. And although coaxial digital connections use standard RCA-style jacks, you'll definitely want to use a coaxial digital audio cable designed specifically for the wider frequency bandwidth of digital signals.

Digital Signal Processing (DSP)
Home theater receivers use Digital Signal Processing for creating soundfields (simulated acoustic environments) and for precise steering of multichannel soundtrack information. When an audio signal is processed and routed in the digital domain, it is less susceptible to signal loss and added distortion.

Discrete output transistors
Found in higher-quality receivers and amplifiers. An amplifier output section comprised of discrete transistors offers some big advantages over the more common, low-cost IC chip amplifier: higher current capacity, ability to handle more heat, quicker response to sonic transients, lower distortion, more dynamic and lifelike sound.

Dolby® Digital
The digital audio format used on the large majority of DVDs, all HDTV programs, and select satellite TV broadcasts, Dolby Digital can include from one to six channels of sound. "5.1-channel" Dolby Digital has 6 discrete digital audio channels: 5 full-bandwidth channels (for front left/right, center, and surround left/right) and 1 "low frequency effects" subwoofer channel.

Dolby® Digital EX
Dolby Digital EX is based on standard Dolby Digital technology (see above), but includes an extra "back surround" channel, making it a "6.1" format. This sixth channel is encoded as a matrixed signal within the standard left and right surround channels, and is reproduced by an additional one or two surround speakers.

You'll need a receiver with either Dolby Digital EX decoding or THX Surround EX decoding to enjoy these 6.1-channel soundtracks. The receiver must also have 6-channel power in order to drive the back surround speaker. Alternately, you can use a 5.1-channel receiver with an auxiliary amplifier or a powered speaker.

A Dolby Digital EX receiver can also use special processing to create 6.1-channel sound from standard 5.1-channel Dolby Digital sources.

Dolby® Digital Plus
A newer version of Dolby Digital found on some HD DVD and Blu-ray high-definition video discs. Dolby Digital Plus can provide up to 7.1 discrete channels of audio. It uses less compression than Dolby Digital, delivering greater sonic detail. You'll need to connect your high-def disc player to a compatible receiver via HDMI or a multichannel analog connection to take advantage of this new format.

Dolby® Digital TrueHD
This surround sound format supports up to 7.1 discrete channels of high-quality audio found on some HD DVD and Blu-ray high-definition video discs. It uses "lossless" compression for the closest possible reproduction of the studio's original master. You'll need to connect your high-def disc player to a compatible receiver via HDMI or a multichannel analog connection to take advantage of this new format.

Dolby Pro Logic®
Pro Logic processing can be found on almost all home theater receivers. It delivers 4-channel playback of Dolby Surround-encoded stereo sources (primarily VHS tapes and stereo TV broadcasts). Pro Logic includes a center channel for on-screen sound; front left and right channels for sound that moves with the action; and a limited-bandwidth mono surround channel sent to the left and right surround speakers to provide ambience and sound effects.

Dolby Pro Logic® II
A big improvement of the original Dolby Pro Logic processing, Pro Logic II gives Dolby Surround-encoded sources a three-dimensionality that approaches the realism of Dolby Digital soundtracks. Pro Logic II transforms any Surround or stereo source — including music — into full 5.1-channel sound. This includes full-bandwidth stereo surround channels and a subwoofer channel.

Dolby Pro Logic® IIx
The newest addition to the Pro Logic family was designed with today's 7-channel receivers in mind. Pro Logic IIx processing can transform Dolby Surround and stereo sources into enveloping 7.1-channel sound, complete with four full-bandwidth surround channels. (When used with 6-channel receivers, Pro Logic IIx yields 6.1 surround sound.)

DTS®
DTS is a multichannel audio encoding system used both in movie theaters and home theater systems. DTS provides 5.1-channel sound, but uses less compression than Dolby Digital. As a result, some say that the sound produced by DTS is slightly more accurate than the sound produced by Dolby Digital. A relatively small number of DTS-encoded DVDs and CDs are currently available, but almost all new DVD players and home theater receivers are now DTS-compatible.

DTS-ES®
DTS-ES is a newer format that gives you 6.1 discrete channels of sound — the 5.1 channels of standard DTS, plus a discrete, full-bandwidth "back surround" channel. That additional channel may be played through one or two speakers, using either a receiver with six-channel amplification, a five-channel receiver supplemented with an additional amplifier, or a powered back surround speaker.

The sixth channel of full-bandwidth sound on a DTS-ES soundtrack is discrete, so some consider DTS-ES an improvement on THX Surround EX, which uses a matrixed sixth channel. Currently, only a few DVDs are encoded with 6.1-channel DTS-ES sound. But for DVDs with 5.1-channel DTS soundtracks, DTS-ES processing can generate a sixth matrixed channel for 6.1-channel sound.

DTS-HD™
A newer version of DTS found on some HD DVD and Blu-ray high-definition video discs. DTS-HD (also known as "DTS-HD High Resolution") can provide up to 7.1 discrete channels of audio. It uses less compression than regular DTS, delivering greater sonic detail. You'll need to connect your high-def disc player to a compatible receiver via HDMI or a multichannel analog connection to take advantage of this new format.

DTS-HD™ Master Audio
This surround sound format supports up to 7.1 discrete channels of high-quality audio found on some HD DVD and Blu-ray high-definition video discs. It uses "lossless" compression for the closest possible reproduction of the studio's original master. You'll need to connect your high-def disc player to a compatible receiver via HDMI or a multichannel analog connection to take advantage of this new format.

DTS Neo:6 modes
Receivers with DTS-ES decoding (see above) also offer DTS Neo:6 modes, which can translate any home theater or stereo source into 6.1-channel sound. Some Neo:6 modes are designed to enhance movies, while others are specialized for music applications.

Dual room/dual source receivers
These receivers let you and a housemate enjoy different sources in different areas of the house simultaneously. For example, many of these receivers allow you to experience the 5.1-channel surround of a DVD soundtrack in your main listening room while a housemate listens to stereo music from a CD in a second room.

Receivers whose dual-room/dual-source output is preamp-level require you to have a separate stereo receiver and set of speakers, or a set of powered speakers, for the second room. A good number of current receivers offer two types of dual-room/dual-source outputs — preamp-level and speaker-level. The speaker-level outputs typically give you the option of using two of your receiver's amplifier channels to power a pair of standard stereo speakers in a 2nd room — no additional amplifier is required. With 7-channel receivers, this means you lose the back surround channels in your main room while powering your 2nd-room speakers, stepping from from 7.1-channel to 5.1-channel surround sound.

Ethernet port
See PC networking.

FM sensitivity
Indicates a receiver's ability to pick up FM signals (a lower number is better).

Full-bandwidth-rated power ratings
When shopping for a receiver, notice the range of frequencies, or bandwidth, listed next to the amplifier power rating. For audio components, "full bandwidth" is generally considered to be the entire frequency range of human hearing — 20-20,000 Hz. Full-bandwidth power ratings are a more conservative measure of power than ratings derived using a narrower range of frequencies.

HDMI™ (High-Definition Multimedia Interface)
A multi-pin connection that can carry both digital video and multichannel audio signals. It's found on many home theater receivers, and some models feature more than one HDMI input for easy switching. For an in-depth look at HDMI, see The Ins and Outs of HDMI.

HDMI video conversion
A growing number of HDMI-equipped home theater receivers offer this highly flexible form of video conversion. It allows your receiver to accept analog video input signals from composite, S-video, and component video sources, convert them to digital, and pass them to a compatible TV via a single HDMI cable. Like other forms of video conversion, HDMI conversion offers the convenience of a single video connection between your receiver and TV, and can eliminate the need to switch source inputs on your TV. However, it won't improve the picture quality of your video sources.

HDMI video upconversion (scaling)
"Upconversion" is the term used to describe the conversion of a lower video image resolution to an apparently higher one. Some home theater receivers can upconvert analog video signals from composite, S-video, and component video inputs and send them to a compatible high-definition TV via HDMI at resolutions ranging from 480p to 1080i (or with some models, as high as 1080p).

HD Radio™
Broadcast radio technology used by some AM and FM stations to transmit over-the-air programming as a digital rather than analog signal. Receivers with built-in HD Radio tuners are capable of decoding and playing these signals. For more information, check out our article about HD Radio.

High-current power
The flow of current through your speakers' voice coils creates the electromagnetic force that moves the cones and domes, creating sound. The dynamic qualities of music and movie soundtracks create short-term high-current demands. If current flow is limited, the sound will be, too. A high-current amplifier (or a receiver that uses one) may sound punchier and more powerful than other models with the same wattage rating.

iPod® integration
Receivers with this technology let you add an optional iPod dock in order to play your digital music through your home audio system. Most docks allow the receiver's remote to control the iPod, and will display a version of the iPod's menu on a connected television for easier operation. Keep in mind, you'll need a dock that's made to work with your receiver.

On-screen display
Some A/V receivers let you view system information and menus on your TV screen. Some use a GUI (Graphical User Interface) for easy remote point-and-click control via on-screen menus and icons. An alternative approach is to display menus and icons on a remote's built-in LCD screen.

PC networking
Some receivers can connect to your home computer network to access music files stored on your PC or a digital music server. They can also give you access to Internet Radio stations via a broadband Internet connection. Connections to the network are typically made through an Ethernet port on the receiver's back panel, or in some cases, using Wi-Fi® (wireless) connectivity.

Phono input
Lets you connect a turntable directly to your receiver. Phono signals are a much lower voltage than other audio signals — a phono input lets you make the connection without the need for a separate phono preamp.

Power amplifier
A power amplifier takes the low-voltage signal supplied by a preamplifier, and increases it to a sufficient level to drive speakers. Receivers contain both preamplfier and power amplifier sections, eliminating the need for a separate amp and preamp.

Preamplifier
Also called a control amplifier or control center. A preamplifier (or preamplifier section of a receiver) handles the switching and selecting of signals, tonal adjustment, digital signal processing, and surround decoding. The preamp also boosts signals to the voltage level required for the input of a power amplifier.

Preamp inputs and outputs
Some receivers and almost all preamplifiers include RCA-style preamp input and output jacks. Used together, these jacks allow you to add an external sound processor or graphic equalizer to your system. The preamp output jacks can also be used to provide unamplified, low-voltage, line-level signals for components like a powered subwoofer or a separate power amplifier.

Receiver
An audio component that combines a preamplifier, amplifier, and an AM/FM tuner in a single chassis. A stereo receiver offers two channels of amplification and is primarily intended for listening to stereo music sources.

A home theater receiver is designed to deliver both music and the surround soundtracks of movies found on DVDs, VHS tapes, and some TV programs. Home theater receivers offer between five and seven channels of amplification, and usually include several types of surround decoding (such as Dolby Digital and DTS).

Remote control
The capabilities of receiver remotes can vary a lot from brand to brand, and even from model to model:

• Audio/video remotes can operate several audio/video components from the same manufacturer.
• Multibrand remotes (also called "universal" remotes) have pre-programmed codes for popular brands of gear.
• Learning remotes (also called "programmable" remotes) can be programmed to carry out specific commands from your other remotes.

Some remotes have RF capability that lets you control your receiver from other rooms in your house — these are especially useful for use with dual-room/dual-source receivers.

Another useful feature of some remotes is an LCD screen that aids in the navigation of system controls. A few of the most sophisticated remotes incorporate an LCD touchscreen that puts even greater system control at your fingertips via customizable control screens. For an overview of advanced remote features, see our article on remote controls.

RMS
A term used to indicate the average level of power that a receiver or amplifier can sustain over a given period of time. Average power ratings (ex: 100 watts RMS) provide a more realistic assessment of your amp's performance than peak power (ex: 400 watts peak/dynamic power) since an amp can only sustain peak power for a short period of time. (RMS stands for "root mean square," which is one of the mathematical methods used to calculate an amp's average power output. While it isn't an accurate descriptor of the measurements themselves, it's commonly used throughout the industry to denote the average power rating.)

Satellite radio ready
Receivers with this capability let you add an optional external tuner in order to receive subscription-based XM or SIRIUS satellite radio. You can change satellite channels using the receiver's remote, and view song titles, artist names, and channel info on the receiver's display (or even on a connected TV screen with some models).

S-video inputs and outputs
Using a 4-pin connector, an S-video jack transmits the chrominance (color) and luminance (brightness) portions of a video signal separately, for improved color accuracy and reduced distortion. Receivers with S-video inputs and outputs offer convenient remote switching for your S-video sources.

Tape monitor loop
An especially versatile type of tape input/output loop found on some receivers and preamplifiers. It allows you to record and play back like a standard tape loop, but can also be used for connecting an equalizer, surround sound decoder, or other external signal processing device.

THD (total harmonic distortion)
A measurement of the accuracy of an amplifier (or the amplifier section of a receiver). THD refers to the amount of internally generated noise. The lower the number, the better.

THX® Select2 and THX® Ultra2
Unlike THX Surround EX (see below), THX Select2 and THX Ultra2 are not surround sound formats. Rather, they are sets of performance standards developed by the engineers at Lucasfilm to ensure excellent audio/video reproduction in cinemas and home theater settings. To garner THX certification, a home theater receiver must meet Lucasfilm's rigorous standards for audio performance, user interface, construction, and compatibility with other THX-certified products.

A THX Select-certified receiver is designed to deliver superbly cinematic performance in rooms up to 2,000 cubic feet with a recommended viewing distance to the TV screen of 10 to 12 feet. The standards necessary for THX Ultra certification are even more stringent, since THX Ultra receivers are required to provide a premium home theater experience in rooms up to 3,000 cubic feet with a recommended viewing distance of over 12 feet.

THX Surround EX™
THX Surround EX provides direct decoding of Dolby Digital EX and Dolby Digital soundtracks. It can also be used in tandem with DTS-ES, DTS, Dolby Pro Logic, or Pro Logic II decoding. In either case, THX Surround EX applies unique processing enhancements such as Cinema ReEqualization™, Decorrelation™ and Timbre Matching™ to increase the realism and impact of the home theater experience.

THX Surround EX decoding is capable of producing 6.1-channel sound from any home theater source. With Dolby Digital EX and DTS-ES DVDs, the 6.1 channels are implicit in the soundtracks themselves (in the case of Dolby Digital EX DVDs, the back surround channel is matrixed in the left and right surround channels). With 4-channel (Dolby Surround) and 5.1-channel (Dolby Digital and DTS) sources, the extra channel(s) are derived using special THX processing.

You'll need a receiver with at least 6-channel power (or a 5.1-channel receiver with an auxiliary amplifier or a powered speaker) to enjoy THX Surround EX's back surround channel.

Ultra-wide bandwidth
Until recently, no common audio technologies existed that could reproduce frequencies much above the audible range of 20-20,000 Hz. New high-resolution formats like DVD-Audio and SACD, however, are capable of frequency response up to 50,000 Hz and higher.

Some higher-end receivers — those designated as having ultra-wide bandwidth — are capable of reproducing these extremely high frequencies. Keep in mind, though, that standard speakers usually have a frequency ceiling between 20,000 and 25,000 Hz. Even with an ultra-wide bandwidth receiver, you'll still need extended definition speakers to reproduce ultra-high frequencies.

USB input
A few newer receivers have USB inputs that let you easily make a direct digital connection between your PC and your receiver. Such a connection allows you to play PC audio — such as MP3, WMA, and WAV files — through your main A/V system. Your PC's sound card is bypassed entirely and the digital-to-analog conversion is handled by your receiver, so you'll enjoy PC audio with the best possible sound quality.

Video conversion
Receivers with video conversion have the ability to accept a variety of incoming video connections from the components in your system and pass them all to your TV through a different type of video connection. Video conversion does not improve the video quality of any of your sources, but it does maintain the best possible quality for each by allowing you to use its optimum video output. The most common types of video conversion are composite to S-video, component, and HDMI conversion.