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  • Signal to Noise Ratio (S/N)
  • Noise Floor

    According to the Wikipedia, "the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system."

    The Wikipedia definition: http://en.wikipedia.org/wiki/Noise_floor

    For our purposes, let's look at a sound card's Line Input used to record from a CD player.

    1. We connect the CD player's analog Line outputs to the Line In on the sound card.
    2. We know the CD player will output a maximum of 2 VAC signal. We set the sound card's Line In level to allow it not to distort (go "in the red") on a 2 V signal peak.
    3. Now we do a test recording, with nothing playing from the CD player.

    We may see that there is a constant noise level in our test recording, at -75 dB (decibels) below the zero (maximum) level. This will be the combined residual hum, hiss and other noise generated by the system (player plus recorder) before any signal is sent from the player to the recorder. That is our "noise floor." We won't be able to record any sounds that are below about 75 dB lower (quieter) than 0 dB ("full-scale," or maximum level, stated as 0 dBFS). If a sound is louder than -75 dB below 0 dBFS, then we'll be able to record it and hear it when we play back the recording. If the sound is quieter than -75 dB below 0 dBFS, then we won't be able to hear it in the recording, as it will be "masked" by the noise ("buried beneath the noise floor").

    The Signal to Noise Ratio could then be said to be -75 dB ("minus seventy-five decibels").
  • Speaker (Loudspeaker)
  • Speaker (Loudspeaker)

    First, check out the Wikipedia definition:

    A loudspeaker (or "speaker") is an electroacoustic //transducer//that converts an //electrical////signal// into //sound// . The speaker moves in accordance with the variations of an electrical signal and causes sound waves to propagate through a medium such as air or water.

    A transducer is a device that changes energy from one state to another, such as electricity to sound (as in a loudspeaker) or sound into electricity (as in a microphone). A light bulb can be thought of as a transducer -- it changes electricity into light.

    A speaker is usually thought of as a complete system consisting of the speaker drivers and the enclosure which houses them. This is more properly referred to as a speaker system.

    The speaker driver consists of a diaphragm (the speaker "cone") connected to a wire coil (the "voice coil") that sits inside the field of a large magnet.
    The positive and negative audio signal from the amplifier is applied to the opposite ends of the voice coil wire (positive and negative; negative is usually connected to common ground). Since the voice coil is sitting in a magnetic field, the magnet causes the voice coil to move back and forth along the voice coil former. Since the diaphragm is attached to the voice coil, the whole diaphragm will now move in time with the audio signal from the amplifier. The diaphragm shakes the air causing large vibrations, and sound is created.

    A picture of the front of a small speaker driver:
    external image 220px-3.5_Inch_Speaker.jpg

    A multiple driver speaker system in its enclosure:
    external image 220px-Lautsprecher_4-wege_2.jpg

    A "Headphone" set has two small speaker systems, one system placed on each ear of the listener. The speaker drivers inside the earpiece enclosures are small because they don't need to play as loud as a speaker system in a room (in "free air"). These headphone "earspeakers" only need to move the air right outside/just inside your ears.

    external image 250px-Headphones-Sennheiser-HD555.jpg

    A "Headset" is a headphone set with a microphone added.
  • Static
  • Static

    "Static" describes a type of noise in audio circuits that has intermittent crackles, pops, snaps and/or ticks, along with a steady sizzling or hiss in the background.

    Some customers will describe a "hiss" noise as "static." However, static noises usually indicate bad connections, cold solder joints or bad wiring, while a hiss noise is usually from poor adjustment of gain levels or a poorly performing or failing amplifier stage.

    Usually, static can be described as something like the sound of bacon frying, complete with intermittent snaps and pops.
  • Stereo vs. Surround
  • Stereo vs. Surround

    Stereo (Stereophonic sound) = Two channels, Left and Right.

    2.1 = a stereo speaker setup with a usually small pair of Left/Right speakers (called "satellites"), and a Subwoofer to play the low bass sounds. A 2.1 speaker setup is not considered a surround sound setup. It's stereo (Left + Right + Subwoofer).

    Surround Sound = Multi-speaker sound that reproduces sounds coming from in front of, to the sides of, and behind the listener.

    5.1 Surround = a Surround Sound speaker setup with a separate channel and speaker for Left Front, Right Front, Left Surround, Right Surround, Center (dialogue) and Subwoofer (Low Frequency Effects or "LFE").

    FL = Front Left
    FR = Front Right
    C = Center
    SL = Surround Left
    SR = Surround Right
    SW = Subwoofer
  • Surround Channels
  • Surround Channels

    Surround channels are audio channels in surround sound multichannel audio. They primarily serve to deliver ambience and diffuse sounds in a film or music soundtrack. Unlike most typical speaker placements, surround speakers are often intended to radiate such that the sound reflects off walls so that the sound arrives at the listening position indirectly as a reflection rather than a direct wave. Often dipole (sometimes even quadrupole) speakers are used to do this, especially in small or home theater applications where an array of surround speakers as in a movie theater is not practical or possible. A common misconception is that surround channels are "rear channels." However, when only two speakers are used, they are meant to be placed on the side walls at 90-110 degrees relative to the screen. Surround speakers are placed above the listeners ears and are not angled towards the listener. In cinema setups, many more than two surround speakers are often used, being placed along the side walls and along the back wall, creating a very diffused sound in the auditorium.

    Surround channels in a 5.1 speaker setup in red

    Surround channels in a Dolby Pro Logic 4.0 system using two speakers in antiphase or a dipole speaker

    Dolby Stereo (1975) was the first standard cinema sound system using a single matrixed mono rear channel (note Disney's Fantasound from the 1930s used a surround channel). Dolby Surround (1982) was the first home audio system to use a rear channel. It and its successor, Dolby Pro Logic (1987), used a single rear surround channel, but often using two speakers connected in anti-phase or a dipole radiator, as shown in the speaker configuration diagram to the right in gray.

    Rear/back surround channels

    Single rear surround channel in a 6.1 system

    Some matrix encoding surround sound systems use a single back center channel surround (Dolby Digital EX, Dolby Pro Logic IIx 6.1) or a back left and back right (Dolby Pro Logic IIx 7.1) speaker configuration. Often the standard surround channels are misconceived to be "rear channels" when they are in fact meant to be placed at 90-120 degrees.

    Surround arrays

    In commercial cinema, where there is a large area to cover, it would be impractical to use a single speaker for each surround channel. Theater auditoriums are often lined with speakers all along the side and back walls. This is to increase the size of the listening area. JBL states that surround speakers should be spaced evenly along the side and back walls, starting at no closer than 1/3 of the room length from the screen (so the surrounds do not interfere with the front channels) and should be located at about 10-12 feet high and angled down to face the opposite wall-floor boundary.

    For music surround channel information is intended to be more direct as in a soundstage there would be direct noise from all around and not ambience as in a movie setting. For this reason surround speakers should not be set up to be strictly diffuse. Optimally there should be discrete surround channels for diffuse and direct effects. This is part of the design for Tomlinson Holman's 12.2 (10.2) surround sound. For movies surround channel information is usually more diffuse ambient noise.

  • THX
  • THX

    THX was started as a George Lucas (of Star Wars fame) venture.

    The purpose of THX certification according to THX:
    "The goal of THX certification is to recreate the power and performance of the cinema and recording studio in your home theater... Testing is precise, rigorous and only the best TVs and home audio systems can achieve THX certification."

    The Wikipedia entry for THX: http://en.wikipedia.org/wiki/THX
    Some excerpts:

    "THX is a trade name of a high-fidelity sound reproduction standard for movie theaters, screening rooms, home theaters, computer speakers, gaming consoles, and car audio systems."

    "The THX system is not a recording technology, and it does not specify a sound recording format: all sound formats, whether digital (Dolby Digital , SDDS ) or analog (Dolby Stereo , Ultra-Stereo ), can be 'shown in THX.'"

    "THX is mainly a quality assurance system."

    "(THX) certification of an auditorium entails specific acoustic and other technical requirements; architectural requirements include a floating floor , baffled and acoustically treated walls, no parallel walls (to reduce standing waves ), a perforated screen (to allow center channel continuity), and NC30 rating for background noise ."

    "THX-certified theaters provide a high-quality, predictable playback environment to ensure that any film soundtrack mixed in THX will sound as near as possible to the intentions of the mixing engineer."
  • TOSlink (Optical Digital or S/PDIF Optical)
  • TOSlink (Optical Digital or S/PDIF Optical)

    or Optical Cable is a standardized optical fiber connection system. Its most common use is in consumer audio equipment (via a "digital optical" socket), where it carries a S/PDIF digital audio stream between components such as DVD/CD players, DAT recorders and home theater receivers. Although TOSlink supports several different media formats and physical standards, digital audio connections using the rectangular EIAJ/JEITA RC-5720 (also CP-1201 and JIS C5974-1993 F05) connector are by far the most common.

    MAXIMUM LENGTH: (from Wikipedia) TOSlink cables are usually limited to 5 meters in length, with a technical maximum of 10 meters, for reliable transmission without the use of a signal booster.

  • Video game console
  • Video game console

    A video game console is an interactive entertainment computer or modified computer system that produces a video display signal which can be used with a display device (a television, monitor, etc.) to display a video game. The term "video game console" is used to distinguish a machine designed for consumers to buy and use solely for playing video games from a personal computer, which has many other functions, or arcade machines, which are designed for businesses that buy them and then charge others to play.

  • Voice Chat
  • Voice Chat:

    Voice chat is a modern form of communication used on the Internet. The means of communicating with voice chat is through any of the messengers, mainly Skype, Yahoo! Messenger, AOL Instant Messenger, inSpeak Communicator or Windows Live Messenger. Voice chat has led to a significant increase in distant communications where two or more people from opposite ends of the world can talk almost free of cost.

    Voice chat in gaming

    Many video games with online multiplayer allow players to communicate via voice chatting. In 2000, SegaNet released the first voicechat compatible browser on Dreamcast. Internet services such as YahooChat! worked on the Java compatible web browsers with the ability of voicechat with the microphone, although it was already available for use in its HTML servers. This browser web integration became in standard in future game consoles. Long-distance telephone Programs such as Dreamcall was already integrated within the browser. Other games such as Seaman and Alien Front Online included voicechat via the microphone. In 2001, Sony released the Network adapter for their PlayStation 2 video game console, which allowed voice chatting with a headset. In 2002, Microsoft launched the Xbox Live service, which supports voice chatting through a headset bundled with the Xbox 360 premium package and the official starter kit. In 2005, Nintendo launched the Nintendo Wi-Fi Connection, an online multiplayer service for both the Nintendo DS and for the Wii. In March 2006, Metroid Prime Hunters was released, making it the first game to allow voice chatting through the Nintendo DS's microphone. Also, Nintendo released a Nintendo DS headset for voice chat alongside the release of Pokémon Diamond and Pearl.

    In the PC Online Gaming Voice Chat world, players often use either the game's built in VoIP engine (which was until recently rarely provided by the game developer), or a third party VoIP solution such as Skype (utilizing the Skype for Power Gamers Skype add-on software), Ventrilo, TeamSpeak, or XFire.

  • Wireless (RF, IR)
  • Wireless: RF (Radio Frequency) - IR (Infrared)

    The easiest way to define this is to imagine replacing the wire/cable that connects the stereo amp/receiver's Headphone jack to the headphone set with a radio frequency receiver and transmitter (no wires, so "wireless").

    WIRED = Amp > Cable > Headphones
    WIRELESS = Amp > Cable > Transmitter > Headset/Receiver

    Simplified explanations of how this works:

    Wired headphones:
    • When using a normal headphone set, the receiver has a headphone amp circuit with a Headphone jack at its output.
    • A cable containing all necessary connections runs between the Headphone jack and the headphone speakers.
    • The electrical audio signal flows from the Headphone jack into the headphones, and the earspeakers play.


    Wireless headphones:
    • Using a wireless headphone set, the Headphone jack on the receiver connects to a transmitter, which converts the electrical audio signal to radio frequency wave transmission.
    • The RF transmitter sends the newly converted audio signal over the air to the headphone set.
    • The headphone set contains a pair of radio frequency receivers, which receive the RF broadcast from the transmitter.
    • The RF signal is then converted back to electrical audio signal, which is then sent to yet another little amplifier in the headphones. The amplified signal makes the earspeakers shake, and you hear the sound.

    You can see that the wireless setup puts the audio signal through many more processes. One would expect some distortions and losses to occur. Certainly there will be some noise added. This is the price one must pay for the convenience of wireless connections. C'est la vie.

    Infrared (IR)

    Infrared radiation (IR) is electromagnetic radiation with a wavelength between 0.7 and 300 micrometres , which equates to a frequency range between approximately 1 and 430 THz .[1]

    Its wavelength is longer (and the frequency lower) than that of visible light , but the wavelength is shorter (and the frequency higher) than that of terahertz radiation microwaves . Bright sunlight provides an irradiance of just over 1 kilo watt per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is visible light , and 32 watts is ultraviolet radiation.[2 ]

    Radio Frequency (RF)

    Radio frequency (RF) radiation is a subset of electromagnetic radiation with a wavelength of 100 km to 1 mm, which is a frequency of 3 kHz to 300 GHz,[1 ]respectively. This range of electromagnetic radiation constitutes the radio spectrum and corresponds to the frequency of alternating current electrical signals used to produce and detect radio waves . RF can refer to electromagnetic oscillations in either electrical circuits or radiation through air and space. Like other subsets of electromagnetic radiation, RF travels at the speed of light .
  • XMB XrossMediaBar
  • The XrossMediaBar (pronounced cross-media bar and officially abbreviated as XMB) is a graphical user interface developed by Sony Computer Entertainment. The interface features icons that are spread horizontally across the screen. Navigation moves the icons, instead of a cursor. These icons are used as categories to organize the options available to the user. When an icon is selected on the horizontal bar, several more appear vertically, above and below it (selectable by the up and down directions on a directional pad).

    Originally used on the PSX, the XMB is used as the default interface on both the PlayStation Portable and the PlayStation 3. Since 2006, it has also been used in high-end WEGA TVs, the BRAVIA starting with the 3000 (only in S-series and above), the Sony XEL-1 OLED TV, HDTV set-top boxes, Blu-ray players, some Sony Cyber-shot cameras and the high-end AV receivers. The Sony Ericsson K850, W595, W760 and W910 feature a version of the XMB as their media menu, indicating that the next implementation of XMB is in Sony Ericsson mobile phones. The XMB is also the menu system in the new generation of Sony's BRAVIA TVs. Sony has also added the XMB to its latest range of VAIO laptops.

    The interface won the Technology & Engineering Emmy Award for "Outstanding Innovation and Achievement in Advanced Media Technology for the Best Use of Personal Media Display and Presentation Technology" in 2006.