Glossary of Audio Terminology

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Index | References




5.1 surround sound The digital audio multichannel format developed by the Moving Picture Experts Group (see: MPEG) for digital soundtrack encoding for film, laser discs, video tapes, DVD, and HDTV broadcast. The designation "5.1" refers to the five discrete, full bandwidth channels - left, right, & center, plus left & right surrounds - and the ".1" usually refers to the limited bandwidth subwoofer channel, but can also refer to a special effects/feature channel. Terminology used by both Dolby Digital and DTS Zeta Digital (the home version of their theater Coherent Acoustics system).

FAQ (frequently asked question) Acronym commonly seen on bulletin boards, Internet Web sites, and corporate information centers. By compiling FAQ lists (FAQs), organizations significantly reduce time spent repeatedly answering the same questions.

fax on demand One of the terms for the process of ordering fax documents from remote machines via telephone, using a combination of voice processing and fax technologies.

FFT (fast Fourier transform) 1. Similar to a discrete Fourier transform except the algorithm requires the number of sampled points be a power of two. 2. A DSP algorithm that is the computational equivalent to performing a specific number of discrete Fourier transforms, but by taking advantage of computational symmetries and redundancies, significantly reduces the computational burden. [It is believed the FFT was first described by Cornelius Lanczos of the Boeing Co. in the 1940's.]

fiber optics The technology of using glass fibers to convey light and modulated information.

filter Any of various electric, electronic, acoustic, or optical devices used to reject signals, vibrations, or radiations of certain frequencies while passing others. For audio use the most common electronic filter is a bandpass filter, characterized by three parameters: center frequency, amplitude (or magnitude), and bandwidth. Bandpass filters form the heart of audio graphic equalizers and parametric equalizers.

Firewall A network component set up to prevent unauthorized network traffic form one side of the device  from crossing to the other side while passing authorized traffic.

Firewire See: IEEE 1394

flanging Originally, "flanging" was achieved using two reel-to-reel tape recorders playing the same program, in synchronization, with their outputs summed together. By alternately slowing down one machine, then the other, different phase cancellations occurred in the summation process. The "slowing down" was done simply by pressing against the flanges of the tape reels, hence the original term "reel flanging," soon shortened to just "flanging." Since the two identical signals would alternately add and subtract due to the introduced phase (timing) difference, the audible effect was one of a sweeping comb filter. It was described as a "swishing" or "tunneling" sound. Soon electronic means were devised to mimic true "reel flanging" by using delay lines and mixing techniques. Adding a low-frequency oscillator to modulate the audio delay line's clock signal created a sweeping effect, much like a jet airplane taking off. The best flangers used two delay lines. Compare with: phaser

Flash Memory Electronic memory chips which are compact in size an do not require continuous power to retain the stored contents.

Fletcher-Munson Curves Fletcher and Munson were researchers in the '30s who first accurately measured and published a set of curves showing the human's ear's sensitivity to loudness verses frequency. They conclusively demonstrated that human hearing is extremely dependent upon loudness. The curves show the ear to be most sensitive to sounds in the 3 kHz to 4 kHz area. This means sounds above and below 3-4 kHz must be louder in order to be heard just as loud. For this reason, the Fletcher-Munson curves are referred to as "equal loudness contours." They represent a family of curves from "just heard," (0 dB SPL) all the way to "harmfully loud" (130 dB SPL), usually plotted in 10 dB loudness increments.

floating unbalanced line A quasi-balanced output stage consisting of an unbalanced output connected to the tip of a " TRS (tip-ring-sleeve) jack through an output resistor (typically in the 50-300 ohms range). An equal valued resistor is used to tie the ring terminal to signal ground. The sleeve connection is left open or "floating." Thus, from the receiver's viewpoint, what is "seen" are two lines of equal impedance, used to transfer the signal. In this sense, the line is 'balanced," even though only one line is actually being driven. Leaving the sleeve open, guarantees that only one end of the shield (the receiving end) will be grounded. A practice that unbalanced systems often require. For troublefree interconnections, balanced lines are always the preferred choice.

FM (Frequency Modulation)  the frequency of the modulating signal is changed in proportion to the input audio signal.

FOH Abbreviation for front of house, used to describe the main mixer usually located in the audience for sound reinforcement systems. Meant to differentiate the main house mixer from the monitor mixer normally located to the side of the stage.

foldback The original term for monitors, or monitor loudspeakers, used by stage musicians to hear themselves and/or the rest of the band. The term "monitors" has replaced "foldback" in common practice

foreground music Officially music with (or without) lyrics used where it is believed people will pay attention to it. Foregroun music is often performed by the original recording artist. Contrast with background music.

Fourier analysis Mathematics. Most often the approximation of a function through the application of a Fourier series to periodic data, however it is not restriced to periodic data. The Fourier series applies to periodic data only, but the Fourier integral transform converts an infinite continuous time function into an infinite continuous frequency function, with perfect reversibility in most cases. The DFT and FFT are examples of the Fourier analysis.

Fourier, Baron Jean Baptiste Joseph (1768-1830) French mathematician and physicist who formulated a method for analyzing periodic functions and studied the conduction of heat.

Fourier series Application of the Fourier theorem to a periodic function, resulting in sine and cosine terms which are harmonics of the periodic frequency. [After Baron Jean Baptiste Joseph Fourier.]

Fourier theorem A mathematical theorem stating that any function may be resolved into sine and cosine terms with known amplitudes and phases.

FPGA (field-programmable gate array) A programmable logic device.

FPS (Frames Per Second) The Frequency at which video frames are transmitted and displayed on a video display.  Broadcast vidio (NTSC standard) containes 60 1/2 frames per second alternating between the even and odd line sets.  Videoconferencing links may support as few as 10 FPS.

Frame Relay A high-speed packet switched protocol used for wide area networks (WANs). It is faster that older x.25 networks, because it was designed for today's faster and more reliable circuits and therefore performs less rigorous error correction.  It provides for scaled transfer rates up to DS1 rates of 1.544 Mbps.

frequency 1. The property or condition of reoccurring at constant measurable intervals. The number of times a specified phenomenon occurs within a specified interval, such as the number of repetitions per unit time for a complete waveform. Usually measured in hertz.

Frequency Response  A measure of a component's ability to reproduce all frequencies equally.  Sometimes called magnitude response, it is the measurement of the amplitude linearity of a component over a given frequency range.  It is usually presented as a plot of the output of a device versus frequency. The term is sometimes used to characterizes the range of frequencies over which a device is designed to operate without stating dB range of variations.  The perfect frequency response should theoretically be flat ( a straight line graph ), however, most components exhibit some dips and peaks in the signal; varying to some degree from a perfect response  Most amplifiers and other electronic audio components can easily reproduce the entire audible spectrum. However, speakers that can reproduce the entire audile spectrum are more difficult to create.  Excessive fluctuations in a curve indicate colorations, which can result in muddy, tinny, boomy or dull sound

full duplex Redundant term. See: duplex

Full Motion Video Compressed video that provides a frame rate that is generally acceptable to users although not of broadcast quality. Typical full motion compressed video provides from 10 to 30 FPS depending on the bandwidth available.



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