Resource Center: How to Speak A/V
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Entries starting with: PAL (phase-alternating line): The analog TV standard for Western Europe except France (see SECAM) and much of the rest of the world except Japan and North America (see NTSC). pan (or panorama): A video shooting technique that swings the camera horizontally over a scene or tracks a horizontally moving object; see tilt. pan-and-scan: A technique for making a widescreen movie fill a 4:3 aspect ratio screen by showing only selected parts of the original image, recropped scene by scene to focus in on what seems most significant to the action. Critics of this technique think the recropping compromises the director’s intent. See letterboxing. parametric equalizer: An equalizer that has variable parameters — such as center frequency, level, and filter sharpness (or Q) — typically to accentuate or reduce its action on user-determined frequency bands. passband: The range, or band, of audio frequencies that a filter lets pass through; see crossover. passive crossover: A network, typically built into a speaker, comprising some combination of capacitors, inductors (coils), and resistors that divides the audio signal into frequency bands (low, high, and possibly midrange) after it is amplified; see active crossover. passive radiator: In a speaker, an unpowered diaphragm that converts the back wave from a woofer into additional bass sound; it functions like the mass of air in the port of a bass-reflex enclosure. PC Card (formerly PCMCIA): A small plug-in card for PCs that enables various high-speed operations, including data transfer through USB and FireWire interfaces and to and from flash-memory media. PCM: see pulse-code modulation. peak (or peak-level) indicator: A visual indicator on an audio recorder that indicates when transient signal levels have exceeded the recorder’s ability to handle them without distortion. perceptual coder: see codec. peripheral: A device or system hooked up to (or sometimes inside of) a computer, like a monitor, printer, hard drive, CD or DVD drive, or speakers. phase: The timing relationship among two or more audio waveforms (signals) or among the frequencies that make up a single waveform. Also, a control that changes polarity. See in phase, out of phase, phase shift, polarity. phase-locked loop (PLL): A circuit used in radio tuners to lock the received frequency to a synthesized reference frequency; see frequency synthesis. phase shift: A change in the timing relationship among a set of waveforms (inter-channel) or among the components that make up the spectrum of a single waveform (intra-channel). phono input: The circuit in a preamplifier, integrated amplifier, or receiver that amplifies the low-level signals produced by a phono cartridge, raising them to the same level as signals from other audio source components (called line-level), and also applies the necessary RIAA equalization. phosphor: A chemical lining the inside face of a CRT that glows when struck by electrons fired by an electron gun. Color CRTs have a repeating pattern of red, green, and blue phosphors named after the colors they emit when irradiated. See dot pitch. picture-in-picture (PIP): A TV function that allows the simultaneous display of two different programs on the same screen, usually with a small image of the subsidiary program(s) superimposed over that of the main program. picture-outside-picture (POP): A TV function that allows the simultaneous display of two different programs on a split screen, usually side by side. piezoelectric: A kind of speaker driver (usually a tweeter) employing a ceramic or other element that bends in response to an applied voltage, generating sound. pink noise: Random noise with equal energy in each octave, used as a test signal; see white noise. pixel (picture element): The smallest subunit of an image that’s treated separately in a digital video system or a non-CRT video display. Pixel counts are often quoted in specs for image sensors, LCD viewfinders, plasma and LCD flat TVs, and LCD and DLP projection TVs; see front projector and rear-projection TV. plasma: A type of video display that employs an enormous array of tiny cells of ionized gas (plasma), which is used to activate each cell’s colored phosphor. polarity: An electrical convention that describes one side of a circuit connection as positive and the other as negative. Reversing, or inverting, the polarity of an audio connection is equivalent to a phase shift of 180°; see reverse polarity. port: An opening (also called a vent) in the cabinet of a bass-reflex speaker that enables the sound wave from the back of a woofer to reinforce the sound wave from the front; acoustically equivalent to a passive radiator. power: The capacity to do work, such as moving a speaker cone. Electrical power is usually measured in watts, as in the output specifications for an amplifier. power amplifier: A component, or part of a component, that strengthens the audio signal from a preamplifier so that it can drive speakers. powered speaker: A speaker, usually a subwoofer, that has an amplifier built in. power supply: A subsection of a component that takes AC line voltage and converts it to one or more DC voltages to operate the rest of the circuitry. In audio, power-supply design can have an enormous influence on noise levels and the maximum output power an amplifier can produce. power tower: A floorstanding speaker that includes a built-in powered subwoofer, either instead of a conventional passive woofer or in addition to one. preamplifier: A component, or part of a component, that switches and processes signals from a variety of source components. preset: A memory circuit that is programmed by the user. For example, tuner presets store the frequencies of radio or TV stations so they can be recalled instantly, and a picture preset stores preferred settings for your TV’s color, brightness, contrast, and so on. programming: The process of entering instructions for a component to carry out at a later time. For instance, many CD players can be programmed to play selected tracks in any order; see macro. progressive scan: A video component or signal that processes or displays each scan line of a video frame in sequence; the alternative to interlaced scan. pulse-code modulation (PCM): Representation of an analog signal by a sequence of multidigit binary numbers. PCM, used for CDs, is the most common digital encoding scheme. pulse-density modulation (PDM): A signal-generation method, used in the outputs of some 1-bit digital-to-analog converters, in which all of the extremely short signal pulses are of the same amplitude and duration but are either positive or negative; the output must be low-pass-filtered to recover the original analog waveform. pulse-width modulation (PWM): A signal-generation method, used in the outputs of some 1-bit digital-to-analog converters, in which all of the signal pulses are of the same amplitude but of varying duration, or width; the output must be low-pass-filtered to recover the original analog waveform. Abbreviations |
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