Glossary of Selected Audio Terms

2.1, 5.1, 6.1, 6.2, 7.1 – see Surround Sound.

Anechoic Chamber – A room lined with acoustically absorbent materials designed to attenuate sound (acoustic energy). Anechoic chambers are used to eliminate the echoes caused by the internal reflections in a room.

Coaxial Digital Cable

Coaxial Digital Cable – A single cable using electrical signals to carry digital sound from a component, such as a DVD player or media server, to a receiver or pre-amp. For an alternative, see Optical Digital Cable.

Helicon Crossover

Crossover / Crossover Network – High fidelity speakers usually contain more than one speaker cone or driver. Typically, a 3-way speaker has a woofer for low frequencies, a mid-range driver for most common sounds (voice and most music), and a tweeter for high sounds. The electronic device that directs sounds of different frequencies to the correct driver is called the crossover.

Dolby, Dolby Digital, Dolby Surround – Dolby Labs is a leader in Surround Sound. Their Dolby Digital surround encoding standard is the most widely used on DVD's and is the standard method of sound broadcast for digital TV, including High Definition.

DTS – An alternative found on DVD's to Dolby Digital, DTS provides higher fidelity sound but takes up more space on the DVD. Most "Home Theater" receivers or pre-amps can decode both Dolby Digital and DTS encoded sound.

Encode/Decode (sound) – Theater sound and music are historically played through analog channels, typically two for stereo and up to as many as eight for Surround Sound (home theater). Encoding, for our purposes, is the conversion of these multiple analog channels into a single stream of digital data that can be stored on a CD, DVD, music server, media server, or can be broadcast over the air. The digital sound takes up much less storage space than the analog equivalent and can be sent to a receiver or pre-amp over a single cable (optical or digital coaxial) where it is decoded back into analog signals that can be played through speakers.

IP (Internet Protocol) – Internet Protocol specifies the format (the layout) and the addressing scheme (how the system knows where it goes) in a network like the internet. It's used in other places besides the internet, and one of them can be a network that passes commands from remote control units to a media server or an automation control device.

IR (Infrared) – A method of transmitting remote control signals to electronic devices using infrared light, which is invisble to the human eye. Most consumer remote controls use IR. This method is strictly line-of-sight and cannot be used to control devices through walls or furniture. As a result, it is often used for home theater but rarely for home automation applicatons like controlling the lights or air conditioning. See RF for a common alternative.

Artcoustic df100-75

Invisible Speakers – Where appearance is the overriding concern, we carry several speaker models that really do disappear into your home's decor. By virtue of the design, they are undetectable as speakers unless they are actually playing. One type camouflages the speakers as various works of art, selected by you, the client. Another type is “taped and mudded” into the drywall, becoming indistinguishable from the surrounding wall. Please note: very few outdoor speakers that are disguised as rocks have met our expectations.

LFE, Low Frequency Effects – These are the very low frequency sounds, usually heard through a subwoofer, which is intended to provide the “feel”; of theatrical movies such as an explosion or earthquake. Surround Sound standards provide an LFE channel (the “.1”) for these effects.

Media Server, Multimedia, Multimedia Server – a computer-based device that provides audio or audio/video data (including “still” photos and text) to an IP distribution network, available to multiple locations. Dynamic content is delivered via streaming technology.

Optical Digital Cable

Music Server – Similar to a Media Server, but audio only.

Near Field – The region, within approximately one meter of the sound source, where the sound pressure fluctuates about a mean value. In the near field, sound waves generated by different points on the speaker may be out of phase and interfere constructively and destructively. The depth of the near field depends on the precise shape of the speaker, the specific location of the measuring device, and the exact wavelength of the sound.

Optical Digital Cable – A single cable using laser light to carry digital sound from a component, such as a DVD player or media server, to a receiver or pre-amp. For an alternative, see Coaxial Digital Cable. The cable is usually made of glass fiber so it can pass light.

Pro Logic II – A digital sound processing technique from Dolby Labs that converts stereo music to surround sound in an attempt to realistically recreate the recording environment (e.g. a club, coffee house, or studio).

RF (Radio Frequency) – A method of transmitting remote control signals to electronic devices using radio waves. Unlike Infrared, RF is not line-of-sight and can operate through walls. RF is often used for home automation applications like controlling the lighting since the receiver/server may be in a different room from the lights. However, RF is not commonly used for Home Theater since Viewers are usually sitting right in front of the television they are watching and IR is more immune to interference. See IR for a common alternative.

SAP, Second Audio Program – Television sound is broadcast in a primary stereo language (e.g. English). However hidden in the television signal there often is a second mono language (e.g. Spanish). Turning on SAP allows the listener to hear the alternate language. The second audio channel can also be used to provide, along with a duplication of the dialogue, a running description of the action on the screen for the visually impaired.

Streaming, Digital Streaming, Streaming Technology – transferring data so that it can be processed as a continuous stream. Streaming originated as an internet technology, developed because most users don't have fast enough access to download large audio or video files in reasonable time. The data is converted from analog form to digital form (digitized data), which conveys much more information in the same bandwidth. The receiving device starts displaying the data before the entire file has been transmitted by collecting the data, which may arrive sporadically, and saving it in a buffer. It then passes the data along at a uniform rate. If the client receives the data more quickly than is needed, the buffer holds the excess. If the data arrives too slowly, its presentation will be sporadic unless a significant amount of it is received and buffered before playback begins.

James 15 Cinema Sub

Subwoofer – A subwoofer is a speaker that produces very low sounds, at least some of which are too low to actually hear. Usually unnecessary for music, “subs,” have been popularized by home theaters because surround-sound movies, like Dolby-Digital DVD's, have special information called Low Frequency Effects or LFE. These are the sounds that make the floor shake during an earthquake or explosion. Since it can take quite a bit of energy to shake a floor, most LFE subwoofers are powered: they have their own built-in supplementary amplifier.

36-SDX In-wall Surround Speaker

Surround Speakers – The side speakers, not the back speakers, in a Surround Sound system. They come in several variations:

  • Direct, where the speaker driver(s) points into the room.
  • Indirect Bipole, where the speaker drivers point along the wall and are in phase.
  • Indirect Dipole, where the speaker drivers point along the wall but are out-of-phase.

Some manufacturers provide surround speakers where the drivers point into the room at an angle, and they can be switched from in phase to out-of-phase. There's disagreement over which of the three methods provides the most “authentic” listening experience, and whether this might depend on the “how” and “why” of the recording.

Surround Sound; 2.1, 5.1, 6.1, 6.2, 7.1 – These are different modes of digital sound and, except for 2.1, represent surround sound. The number before the decimal point represents the number of encoded channels. The number after the decimal point is the number of LFE (Low Frequency Effect) Channels. This is almost always one, and represents the subwoofer. For example, 5.1 means two main (stereo) speakers, one center channel (for most voice) and two surround speakers (to the left and right sides, not behind, the movie-watchers) for a total of five channels. The “.1” means there is a channel for LFE (i.e. the floor shaking for an explosion or earthquake). This sound is usually sent to one or more powered subwoofer(s). (Just because your theater has two—or more—subwoofers does not mean you have more than one LFE channel.) 6.1 and 7.1 mean there are one or two additional speakers. These are placed behind the listener.

THX – An audio and video standard for movie reproduction. Originally put forward by George Lucas, this tells how a DVD player should produce a picture and how the surround sound channels should work. There are many flavors of THX including Select, Ultra, and Ultra 2. Many people contend that good THX reproduction is often not good music reproduction. Ultra 2 addressed some of this critcism.

Wireless – A system of controlling a device with a “remote.” The Remote Control can signal the device using either Infrared (IR), or Radio Frequency (RF).