Main Glossary A - E F G H I J K - O P - T U - Z

- F -

 

FCC

Federal Communications Commission. The regulating body for radio and television transmission in the USA.

 

FET

Field-Effect Transistor.

 

FFT (Fast Fourier Transform) analyzer

One notable use is in speaker testing, where it is used to simulate anechoic testing conditions without employing a special chamber. It is best at plotting frequency and phase characteristics, but must be used with care if real-world listening conditions in more reverberant environments are to be considered. A mathematical operation used to test a variety of audio (and other) components.

 

FM

Frequency Modulation. A radio-transmission technique that conveys data by encoding audio signals as variations in the frequency of the carrier signal.

 

Far field

A listener is in the far field when each doubling of the distance from the source results in a reduction of 6 dB in sound level, due to the inverse-square law. The far field exists between the near field and the reverberant field and is typically from 2 to 3 times the distance between the most separated points of a speaker system that are radiating at the same frequency. For practical purposes, consider it to be the point where the reflected energy begins to dominate over the direct sound energy. Therefore, its location may vary with frequency, becoming closer to the speaker system at low frequencies or at higher frequencies if the system has excellent high-frequency dispersion, and farther away at crossover points or at frequencies where the system has limited dispersion.

 

FerrofluidTM

Originally developed as a rotary seal, this substance is a magnetically attracted liquid that works well at cooling tweeter and midrange driver voice coils. This is because it stays suspended in the magnetic gaps between the coil and the heavy magnet assembly, conducting heat to the latter. It also can affect speaker damping. In some tweeter designs, silicone grease will work better than Ferrofluid.

 

Fiber optics

A form of signal transmission that allows digital data to be transmitted as pulses of light, normally through special cable. The main advantage is a reduction of noise and distortion.

 

Figure-eight microphone

A microphone with a dumbbell-shaped pickup pattern that is sensitive to sound from the front and rear but not from the sides. Variants include super- and hypercardioid models, which have less sensitivity to the rear and somewhat more to the sides. See also Dipole.

 

Flat response

In audio, a condition whereby a signal is not boosted or attenuated at specific frequencies over its operating range.

 

Flat-screen picture tube

Direct-view television picture tube with a flatter front surface (and usually shallower depth) than older (or cheaper) designs, allowing for a more undistorted picture, particularly when viewed from off to the side somewhat.

 

Flutter

A variation from exact speed, normally found in analog recording and playback devices. Called "wow" when the variations are slow, flutter is not a problem with digital record-playback Systems, because their outputs are controlled by internal clock mechanisms. See also Wow.

 

Flying erase head

An erase head built into a rotating VCR head drum. Most decks have the erase head mounted in a fixed position, limiting editing flexibility. The flying head makes it possible to do clean edits.

 

Focus

In two-channel audio, focus relates to the ability of a recording or pair of speakers to keep sound-stage images-especially those in the central area-properly sized and positioned. See also Center channel; Imaging.

 

Frame

In video, one complete image on a TV screen that has been formed by progressive or interlaced scan lines. See also Progressive scan; Interlaced scan.

 

Franssen effect

See Precedence effect.

 

Free field

The condition whereby a sound reaches the listener without having been reflected from any surface. Often misnamed the near field, although the latter exists at distances much closer to the sound source.

 

Frequency

A rate of vibration or signal oscillation. In audio, it normally involves the audible bandwidth. In video, it most typically involves the bandwidth of the sharpness component of the video signal, although the bandwidth of the color component of the signal is often of greater importance.

 

Frequency response

Sometimes called magnitude response, it is the measurement of the amplitude linearity of a component over a given frequency range. Frequency response is probably the most important aspect of audio system performance but there are different opinions about what is to be measured. A big problem with many recordings, even some contemporary ones, is that the microphones chosen to make them often have poor frequency response. The biggest problem with some of the studio-monitor speakers that are still being used to edit those recordings is their limited or ragged frequency response, particularly in the reverberant field. Using studio-located equalizers to compensate for those deficiencies results in recordings that are improperly equalized for playback on high-quality home speakers. See also Direct field; Reverberant field.

 

Front-to-back (F/B) ratio

The F/B ratio relates to an antenna's sensitivity to signals from the front compared with its sensitivity to signals from the rear. In TV and FM radio reception, assuming the antenna is aimed properly, a higher ratio will help prevent ghosts and multipath distortion.

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- G -

 

Gain

The amount of amplification developed by an amplifier, preamplifier, etc.

 

Ghosts

See Multipath distortion.

 

Golden ear

A term describing audio buffs who have the (real or imagined) ability to hear subtle differences in recorded sound.

 

Gray-scale linearity

In video, an indication of how accurately a VCR, disc player, or TV set handles subtle variations of gray-from lighter shades down to near black.

 

Ground

The zero-voltage reference used to signify a negative connection.

 

Group delay

The frequency-dependent variation in signal delivery time from an audio component. In loudspeaker Systems, this can result from crossover anomalies or differences in listening distances. Many speaker manufacturers "time align" the drivers to compensate for group-delay problems, but these solutions only work if the listener is locked into a specific location and the system is auditioned from very close up. At normal listening distances, the group delay from any decent loudspeaker system is inaudible.

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- H -

Haas effect

See Precedence effect.

 

HDTV

High-Definition Television.

 

Hafler circuit

An ambience-recovery circuit designed by David Hafler in the 1960s. The L-minus-R matrix principle that is its basis is similar to what is employed in the Dolby Surround version, but without the need for extra amplifiers.

 

Hard matte

See Matting.

 

Harmonic distortion

The most common form of audio distortion, it shows up as additional unwanted signals at multiples of the original frequency. Thus, a l -kHz tone may have second-order harmonic distortion at 2 kHz, third-order at 3 kHz, etc. These can continue upward to beyond the seventh or eighth order. The percentage total of all these measurements is called total harmonic distortion (THD) and is commonly used in audio test reports. However, different components generate different ratios of odd and even orders, making some sound better than others-even though their THD measurements maybe the same.

 

Heads

The parts of an audio or video tape recorder that lay down or pick up the magnetic signal on the tape.

 

Hi-fi video

The videotape medium that makes use of specially encoded signals to carry the audio part of the video program. The Beta version uses the video heads on the rotating tape drum. The VHS system has separate audio heads-also on the tape drum-in addition to the video heads. Newer formats employ digital audio.

 

High-pass filter

Within an audio crossover network, the electronic or passive circuitry that allows the high frequencies to go to a speaker system or amplifier. See also Low-pass filter.

 

Home-theater system

An audio-video system that is high enough in quality to simulate a theatrical experience in the home. While most video components, especially television sets, may be inadequate to achieve near perfection, good results in the audio realm can be had for a reasonable amount of money.

 

Horizontal resolution

In video, one of the more common specifications listed by manufacturers. It is the ability of a component (television, VCR, disc player) to resolve detail sideways across a television screen. Many NTSC television monitors have horizontal-resolution capabilities well beyond any source material they might have to reproduce, making the one-upmanship battle of resolution specifications more of an advertiser's tool than something significant. This measurement can be calculated either from a component's video frequency response or by means of a resolution chart on a monitor.

 

Hz

Hertz, or cycles per second (cps), or pitch. The name comes from Heinrich Hertz, a German physicist.

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- I -

IC

Integrated Circuit. A miniature electrical circuit.

 

IDTV

Improved-Definition Television. IDTV sets employ digital line-doubling circuitry, which allows NTSC-spec interlaced scan lines to simulate a more artifact-free progressive scan. See also Interlaced scan; Progressive scan.

 

 

IEC

International Electrotechnical Commission.

 

IEEE

Institute of Electrical and Electronic Engineers.

 

IHF

Institute of High Fidelity.

 

IPS

Inches per second.

 

ISO

International Standards Organization.

 

Imaging

The ability of a component (usually a loudspeaker pair) or recording to form a realistic sound stage with precise instrumental and/or vocal localization. In fact, imaging is often more dependent upon recording techniques than speaker-system design. A few speaker systems, when reproducing certain recordings, perform imaging feats that even live music cannot duplicate.

 

Imaging Science Foundation (ISF)

An organization founded by Joe Kane to promote the correct alignment of existing TV picture systems and improve the quality of future systems.

 

Impedance

In a DC (direct current) circuit, the same thing as resistance. In an AC (alternating current) circuit, impedance is the complex interaction of inductive and capacitive forces-in addition to resistance. In such a circuit, impedance is dependent upon frequency. See also Resistance; Input impedance; Output impedance.

 

Indexing

With audio (DCC and MiniDisc) and video recorders, this is the ability to electrically mark a point on a tape or disc for later access. Some CD, LV, and DVD players also have an indexing playback function, but it will only work with discs that are specially encoded with indexing points.

 

Infinite baffle

If the front of a loudspeaker driver is acoustically isolated from its back, it is said to be operating in an infinite baffle. Practical limitations result in enclosures behind drivers that still isolate the rear from the front. See also Dipole; Acoustic-suspension speakers; Electrostatic speakers; Planar-magnetic speakers.

 

Infrared

A part of the electromagnetic spectrum that is just below the frequency range of visible light. Most remote controls work with infrared light.

 

Infrasonic filter

A type of high-pass filter that attenuates frequencies below the audible range-reducing the work that woofers and amplifiers must do when reproducing signals that contain very low-frequency, but audible, sounds or even subsonic energy. Useful with LP-record playback to limit annoying record-player and cutting-lathe rumble and the studio or hall noise present on some CD recordings, particularly those made in churches and older halls.

 

Input impedance

The "load" actually seen by a source connected to an input. In audio, the input impedance should be considerably larger than the connected component's output impedance to avoid signal losses and frequency-response irregularities. In video, the input and output impedances should nearly match.

 

Integrated amplifier

Sometimes called a control amplifier, this is a receiver minus a tuner or, if you like, a power amplifier plus a preamplifier. Some integrated amplifiers are very elaborate and contain A/V switching and even surround-sound processing.

 

Intensity stereo

See Coincident-microphone recording.

 

Inter-aural cross-talk

An effect created when the signals from a pair of stereo speakers are heard as individual events, rather than a coherent, single one. This effect can muddy stereo imaging and sound-stage realism. See also Cross-talk.

 

Inter-aural cross-talk cancellation

By emitting out-of-phase cancellation signals to null inter-aural cross-talk, this process can improve focus and sound-stage imaging. To work properly, it requires the listener to sit exactly in the sweet spot, out in front of and exactly between the speakers. The effect can be influenced by early room reflections, and some listeners think the process adds substantial sound-stage phasiness. It is available on some recordings in the form of the Q-Sound, Spatializer, or Roland RSS systems; variant designs that work with conventional recordings are also available in home processors made by Spatializer, Carver, and Lexicon, as well as in Polk Audio's SDA speaker systems. See also Early reflections; Phasiness; Sweet spot.

 

Interlaced scan

The process of imaging a television picture by having the numerous scan lines that form the picture laid down at two intervals, with each positioned adjacent to the other. Done correctly, it allows for a sharper picture at any given transmission bandwidth. See also Progressive scan.

 

Intermodulation distortion (IMD)

Electronically similar to mechanical Doppler distortion in that it results from a higher-frequency signal distorting as it rides on one of lower frequency. Unlike Doppler distortion, the one-dimensional nature of IMD within an electronic component can make it quite audible. See also Doppler distortion.

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- J -

Jog/shuttle dial

A control dial found on some VCRs and laser-video players that allows the user to more easily execute forward and reverse picture searches.

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Revised: February 13, 2004.
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