A Guide to Understanding AV Receiver Ratings, Specifications, and Terminology

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There are several perfectly acceptable ways to set up a home theater system. A popular version that you can read about here on Bright Hub involves using a media center PC for the command and control center for the entire system. This has the advantage of including home networking and network storage.

Another perfectly suitable and popular setup, and the one we’ll look at here, is to use an audio/video receiver as the center of the home theater system.

Most stereo receivers sold today have some way of interacting with a television or television accessories. This might include accepting input from the television or set-top box and decoding certain sound streams. Dolby processing would be an example of a common feature. A dedicated audio/video or A/V receiver, however, is more concerned with providing outputs to the television and doing the sound processing from the source stream itself. All serious A/V receivers provide some sort of surround sound with support for multiple speaker placement. Some can even take a standard definition video signal, like from a DVD, and scale it up to high-definition 1080p size, or take a standard stereo audio source and turn it into surround sound.

A/V receivers are available from about two-hundred to several thousand dollars. All have long lists of features and specifications, but what do all the terms, ratings, and numbers really mean? Can comparing the specifications and features help the potential purchaser decide on a specific receiver?

We think so. Knowledge is a significant tool in a consumer’s arsenal. Understanding specifications and terminology will help you select the best AV receiver for your home theater system.

Comparative Specifications

First, let’s look at ratings and specifications that can be expressed as numbers.

RMS Power Output, Peak Output Power, and Surround Power

RMS power output is the amount of maximum power, measured in watts, that the amplifier in the receiver can continuously provide to each channel in stereo mode. In general, the receiver that has more output power is more desirable. Peak output power refers to the momentary loudness increases that the amplifier can provide, such as for a drum rift or an explosion.

RMS power output in a surround mode is called “surround power.” When denoted in a form like “90 x 5,” it means that the amplifier can provide 90 watts RMS power output to five surround channels.

Total Harmonic Distortion

Total harmonic distortion, or THD, is a measurement of the accuracy of the amplifier. It’s expressed as a percentage of the total output. Anything less than about 1% THD is considered good, but some receivers are capable of .1% THD and better these days. Another way to look at THD is that of it being a measure of the internal noise generated by the amplifier circuitry. In comparing receivers, less THD is better.

Frequency Response and Bandwidth Response

Frequency response is a measure of the range from the lowest pitched sounds to the highest pitched sounds the amplifier can provide. Bandwidth response is a much more useful measure for comparing A/V receivers. It is the frequency response that the amplifier can provide at the rated RMS power output.

Most humans can hear from about 20 to 20,000 Hz, so this is the range that many manufacturers claim. Claiming much lower would be dubious (and useless), but claiming higher would be acceptable.

Next: Surround Sound Encoding and Processing

Surround Sound Encoding and Processing

A/V receiver specifications usually list the types of surround sound decoding of which they are capable. Of course, you first need a source that contains the encoded stream that also uses the same decoding scheme. Since different sources have different encoding modes, it is desirable that an audio/video receiver support several different modes.

For example, Dolby True HD and Digital Plus are recent decoding methods found on some newer Blu-ray discs. If your future plans include an investment in Blu-ray, these would be very desirable decoding modes to have. As another example, if you have a large library of CD audio or DVD videos, Dolby Pro Logic would be a good feature.

In general, it’s better to have a high-end surround sound decoding feature that you don’t need yet than to settle for an alternate less-capable process. (This variation in decoding features is why most DVDs and Blu-ray discs have multiple encoding.)

Dolby Digital

First proposed in 1990, Dolby Digital became the default audio format for DVDs and HDTV, as well as for some satellite TV broadcasting. It is a “5.1” system consisting of right, left, and center front speakers, and two right and left rear speakers. The .1 refers to the subwoofer, or very low frequency output. The subwoofer is an important element in providing an immersive listening experience in a home theater, allowing sound pressures that can be felt as well as heard. As this is the oldest standard, all A/V receivers should be expected to support it.

This, by the way, does not preclude using the receiver with fewer speakers. 2.1 and 4.1 would still be decoded and sent to the proper speakers.

Dolby Digital EX

Dolby Digital EX provides 6.1. It adds a sixth channel obtained from mixing together the right and left surround channels. Of course, the receiver should have six powered speaker outputs in order to support this encoding mode. EX is beneficial because it increases the sound pressure, again, helping to provide that immersive experience.

Dolby Pro Logic

Dolby Pro Logic II and IIx are encoding standards that create surround sound from any stereo source, including analog signals from phonographs and VCRs. It works by slightly changing the phase and delay of the sounds going to each channel. This increases the stereo separation and can simulate a multi-channel soundtrack using two front and two rear speakers.

Dolby Digital Plus

Found only on some newer Blu-ray discs, Dolby Digital Plus provides 7.1 channel audio. It is presented in a faster data stream than Dolby Digital, with less compression, and thus it is more realistic and accurate than what can be obtained from standard DVDs. You’ll need an HDMI input in order to decode this.

Dolby True HD

Also found only on some newer Blu-ray discs, Dolby True HD supports 7.1 channel audio and uses “lossless compression” that provides a more accurate reproduction than Digital Plus. Again, an HDMI input is required in order to decode this.

DTS Encoding

Think “movie theaters.” That’s where this 5.1 digital audio format came from. It stands for “Digital Theater Systems” and the standard is owned by DTS, Inc. Very few DVD or CDs support DTS, but some DVD players and A/V receivers do support it. (It was also briefly popular on Laserdiscs - right before DVDs supplanted them.)

DTS ES adds a one or two speaker back surround channel, making the output 6.1.

DTS Neo:6, like Dolby Pro Logic, works with standard stereo audio, except that it generates 6.1 and has different modes for movies and music.

THX Encoding

Brought to us by the folks at Lucasfilm, this all-encompassing standard includes requirements for construction, compatibility, user interface, and, of course, audio performance. Most home users interested in this encoding format would look at the “THX Select” certification. This covers up to 2,000 square feet. “THX Ultra” increases the coverage to 3,000 square feet.

Few A/V receivers support THX encoding. Those few that do currently range in price from about $800 to over $5,000.

Next: Standard Ports and Connections

Standard Ports and Connections

Just as a good audio/video receiver will include a number of surround sound decoding schemes, the receiver is also likely to have a great variety of connection options and associated input and output ports. Many are now standardized, but the best receivers provide legacy support for older connection types as well as the most current, protected content digital streams such as Blu-ray video and audio over HDMI.

HDMI Inputs and Outputs

HDMI stands for High Definition Multimedia Interface. It’s a standard interface for connecting components that carry media through protected streams, such as Blu-ray disc video. HDMI is necessary to support HDCP (high-bandwidth digital copy protection) and carries both high-definition video and the decoded audio streams.

It’s best to have multiple HDMI inputs - at least one for every high-definition source that you plan to manage through the A/V receiver. Three HDMI inputs are acceptable, but a single HDMI input, for purposes of future expansion, is not a desirable feature.

A single HDMI output is most common for home theater A/V receivers, although some higher-end gear have two or more.

Composite, Component, and S-video

Composite video is the familiar connection to red, white, and yellow cables with RCA-type jacks that carries left and right audio and standard definition video. They are used to connect DVDs and VCRs, but are not used with high-definition digital streams.

Component video is similar to composite, but it uses three cables to carry the video - one for luminance and two for color (or chrominance). This was fashionable for a while, mainly with large wide-screen TVs, but the advent of HDMI has largely removed the need for component video.

S-video is an improvement on composite inputs. S-Video input is desired as it’s the best way to get a good signal from a standard DVD player. S-video contains one conductor for luminance and one for color.

Since S-video is a common connection found on standard DVD players, it’s good to have at least one input and one output on an A/V receiver. (The receiver, of course, will provide quick switching between your standard and high definition sources.)

Optical Digital Inputs and Outputs

Optical digital inputs and outputs require a fiber-optic cable. Also known as “Toslink,” the advantage of this type of connection is that the signal is not affected by radio frequency or other electromagnetic interference.

Optical inputs are more commonly found on A/V receivers than optical outputs. This is because few home theater setups include any recording devices that have a Toslink input.

One or more optical digital inputs are desirable on an A/V receiver, but the optical digital output can be considered optional or unnecessary as the receiver itself should be the primary audio component in the system.

Low Level Inputs and Preamp Outputs

Also known as “Phono Inputs,” low level inputs are used to connect devices such as phonographs. Preamp outputs are exactly the opposite of low level inputs - they provide a low level output suitable for connecting external amplifiers. A receiver may also have a separate preamp output for a powered subwoofer, but most receivers can drive the subwoofer directly.

Unless you plan to include a turntable in your system, you probably won’t be using any low level input on your receiver. Likewise, the trend today is certainly not toward external amplifiers. The receivers themselves are powerful.

Next: Major Features and Conclusion

Other Features

This section covers some of the major features that may be included in an audio/video receiver.

HDMI Switching and Video Conversion

HDMI switching simply means that whatever input from any source you select will be sent to the HDMI output. HDMI switching is a highly desirable feature, and only the rudest, most minimal A/V receivers will lack it.

Video conversion works in conjunction with HDMI switching. It’s the ability to take any input, whether it be composite, component, S-video, or an HDMI input, and send it to the main HDMI output for the HDTV. Some A/V receivers are quite elaborate about this and can provide video conversion that does not just go to the HDMI output. For example, they can convert S-video to composite or composite to component. This is not a terribly difficult feature for the manufacturer to implement, but it’s very handy if your home theater setup includes gear from different generations. A DVD-R, or DVD Recorder, with S-video and composite inputs would benefit by using the S-video output, for example.

1080p Up Conversion

This is the ability to take any source at any resolution and output 1080p. It’s useful for “up converting” standard DVD (480p) to the full resolution of the television. Receivers have a small CPU dedicated to this task that manufacturers like to brag about. A few years ago this was a big selling feature that differentiated different receivers, but now the hardware is common and inexpensive, and a good A/V receiver should be able to do 1080p up conversion.

Digital Signal Processor

The previously mentioned CPU that handles up conversion is also responsible for surround decoding, digital to analog conversion, and analog to digital conversion. It’s known as the DSP, or digital signal processor. Manufacturers make lofty claims like “32-bit floating point processor” or “400 MIPS processor,” but it’s generally safe to assume that the DSP is fast enough to do the conversions and surround processing that the manufacturer lists elsewhere in the specifications.

Main and Multi-Zone Speaker Outputs

All A/V receivers will have at least one set of speaker output terminals. Some receivers have two pairs of speaker outputs, allowing music to be “piped” into another room. In this case, the user is allowed to switch between the speaker sets using a toggle between set A and B.

Multi-zone, on the other hand, means that the second set of speaker outputs can play independently of the main set. In other words, the multi-zone speaker set does not have to play from the same source as the main set - it can play something totally different. This is a high-end feature not found on inexpensive receivers.


Well, that’s it for now. If you’re looking at a feature or specification that we haven’t covered here, please leave a request in comments. Comments are moderated, so there will be a short delay before they appear, but we’ll reply to all comments.

Thank you for reading this. We wish you good luck in your selection of a suitable home theater audio/video receiver. Thanks, too, for visiting Bright Hub.