Click on a letter or number to jump to listings of terms that correspond. [ 5 | A | B | C | D | E | F | G | H | I | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y ] Term Definition Demo PAL The television broadcast coding standard used in England, Europe, and many countries in the rest of the world. It has 625 lines displayed at 50 fields/second. Of these, about 576 lines contain picture information. See: NTSC, SECAM, Television Systems. Pan and Scan A method of converting widescreen programs and movies for viewing on a standard 4:3 aspect ratio television. It involves rerecording the program while panning and scanning (sweeping left and right) with a camera, selecting the portion of the picture to be shown in the reduced size. Obviously, the result is not the same movie that the director created, but it fills the entire TV screen. Letterboxing is the alternative. See: Letterbox, widescreen, aspect ratio. Parallel Connection Connecting two or more devices across the same terminals so that each device carries the full applied voltage. In loudspeakers, parallel connection of two identical units halves the impedance seen by the power amplifier, which can create problems with amplifiers not able to drive low impedances. For example, two 6-ohm loudspeakers operating together will present a 3-ohm load, which is below the safe operating load range for many power amplifiers. This is a consideration in the A, B, A+B loudspeaker switching feature of A/V receivers. See Series Connection. Parametric Equalizer An equalizer consisting of several filters each of which can be adjusted in each of three parameters: frequency, bandwidth or Q, and amplitude, allowing it to closely match the properties of resonances which are to be attenuated. See:Resonance, Graphic Equalizer. Particle Velocity Air is constantly in motion due to wind or thermal convection currents. The particle velocity of interest in audio is that which is added by the alternating pressure fluctuations of sound as it passes through. Due to sound alone, particles stay in place and simply vibrate. Pass Band See Bandpass. Passive Radiator Often called a "drone cone." A diaphragm with a suspension but no motor assembly. Passive radiators can be substituted for a vent or port in a speaker. PCM A straightforward, uncompressed coding method in which analog signals are sampled at regular intervals, and each sample is represented by a digital number representing the amplitude at that instant in time. Sampling is done at a frequency at least two times the highest frequency of interest, and the digital number must have a sufficient number of bits to capture and reconstruct the essential qualities of the audio signal (dynamic range, low distortion and noise, etc.). For example, typical CDs are recorded using a sampling frequency of 44.1kHz, using a 16-bit digital number. See Bit, Compression. Peak In time: the instantaneous maximum value of a time-varying quantity. E.g. peak power in power amplifiers. In frequency response: an elevated output that is concentrated over a narrow range of frequencies, describing a peak in the frequency response curve. Perceptual Coding A method of processing a digital audio signal in which knowledge of auditory masking is used to predict what portions of the signal would not be heard by normal listeners. These portions are then either discarded, or more simply encoded, so that the data rate used to communicate the signal is reduced, as is the storage capacity. Several such "lossy" coding systems exist, and they all sound excellent at high data rates, degrading by different amounts in different ways as the data rate is reduced. Perforated Panel Absorber A form of acoustically resonant absorber in which a Helmholtz resonance is created with the air mass in the perforations reacting with the compliance of the air behind the perforated panel. See Resonant Absorber, Helmholtz Resonance.. Period The time interval between identical points in a periodic signal or sound. For a sinusoid (single frequency) the period (in seconds) is calculated as 1 / frequency (in Hz). See Periodic. Periodic In this context, a sound wave that repeats itself exactly at regular intervals. The simplest of these is a pure tone, a single frequency. Phantom Center In stereo or surround-sound systems, a phantom center image is perceived when the same sound is radiated from left and right loudspeakers, and the listener is exactly equidistant from both loudspeakers. In multichannel systems, it may not always be possible to use a real center channel loudspeaker, in which case, a phantom center can be selected (or will occur automatically when no center loudspeaker is indicated to the surround processor during setup). A real center loudspeaker is advantageous because the sound image is heard to be in the same place by listeners in different locations. See: Center Channel, Stereophonic. Phase For a single frequency, a periodic signal, the repetition period is divided into 360 degrees. Phase is measured as angular degrees within the period. For a single frequency, there is an equivalent time for a given phase shift, but the time for a given phase shift will be different for every frequency because the period is different for every frequency. 180-degree phase shift is equivalent to a polarity reversal. See Phase Shift. Phase Adjustment (Subwoofers) Because they are in different locations in a room, the sound from a subwoofer and that from the satellite loudspeakers do not always combine properly, resulting in too much or too little sound in the crossover region. This is a control allowing the user to make small adjustments to the phase of the subwoofer in the hope that the situation can be improved. Sometimes it can. See: Phase, Crossover. Phase Plug In a compression driver for a horn, this is a device conveying sound energy from the large diaphragm to the smaller throat of a horn in such a way that, over most of the operating frequency range, sound originating at all parts of the diaphragm arrive at the throat in phase. See: Horn, Compression Driver, In Phase, Throat. Phase Response A measurement of phase as a function of frequency from the input to the output of an audio component. See Frequency Response, Transfer Function. Phase Reversal See Polarity Inversion Phase Shift A change in phase angle between the input and output of a device or system. This would normally be specified at several frequencies, or as a continuous curve as a function of frequency. Phon A measure of perceived loudness originated by Fletcher and Munson. The loudness level, in phons, is the sound pressure level of a 1 kHz pure tone that is judged to be equally loud. Each of the equal-loudness contours, therefore, is identified in phons. See Equal-Loudness Contours Phono Input/Preamplifier An input designed to accept the small voltage signals from a phonograph cartridge, to amplify them to normal line levels and to perform the inverse RIAA equalization necessary to produce properly balanced low and high frequency sounds. See: RIAA Pincushion Distortion Geometric distortion in video pictures in which straight lines take on a concave shape, curving inward from the screen edges between the picture corners. See: Barrel Distortion Pink Noise Random noise having a continuous spectrum and energy distributed equally on a percentage-bandwidth (e.g. octave, 1/3-octave) basis. Commonly used for audio measurements since the energy distribution is close to that of music. See: White Noise Pitch The perceived quality of sound that is most closely related to frequency, but is also influenced by sound level. The position of a note on a musical scale. Pixel The smallest element in a picture. An individual dot in a picture composed of dots, as in all digital video systems. PLUGE Stands for: Picture Line-Up Generation Equipment. A test pattern used for setting the black level (brightness at the darkest part of an image) of a video display. Polarity Being electrically positive or negative, as in the terminals of a battery or DC power supply. Being, at an instant in time, positive or negative, relative to zero voltage, in an AC signal. Polarity Inversion In an AC signal path, to reverse the connections (as in a loudspeaker), or to invert the waveform (as in electronic circuitry). Sometimes confusingly called Phase Reversal - meaning that the instantaneous phase at all frequencies is simultaneously reversed by 180 degrees. See Phase, Out-of-Phase. Pole Piece The cylindrical core of a loudspeaker motor, one end of which forms the inside of the magnetic gap within which the voice coil moves. Polypropylene Thermoplastic used in speaker diaphragms. Polypropylene is weather resistant and well damped. Port A vent or tube that forms part of a resonant system in a bass reflex loudspeaker enclosure. See Bass Reflex. Potentiometer A resistor with an adjustable tap, used for many purposes in electronics, including the common one of volume control. Power The amount of energy delivered or used by a device or system, expressed in Watts. In audio, power ratings of amplifiers and loudspeakers are subject to a lot of variation and uncertainty because of the very large difference in the long-term, steady-state, power rating, and the transient, or momentary, power rating, which can be several times larger. Further confusion is added when ratings at a single frequency (say, 1 kHz) are compared with the more realistic 20 - 20 kHz rating. In multichannel amplifiers, there is the further variable of ratings done with a single channel operating vs. ratings with all channels operating. The result, for consumers, is that advertised power ratings are often almost meaningless. Power Compression In loudspeakers at high sound levels, an effect in which the acoustical output of the device increases less than the electrical input to the device. Caused mainly by the heating of the voice coil, and the consequent increase in electrical resistance. In multi-way systems, power compression affects the different drivers differently, causing the loudspeaker system to have a different spectral balance at different sound levels. Power Handling The amount of power that may be applied to a device without causing destruction. May be expressed as "RMS" or as "continuous average" to indicate how much power can be applied for long periods. It mnay also be expressed as "peak" to indicate how much power can be applied for extremely short periods--the beat of a drum, for instance. See also Power Power Rating See: Power. Powered Tower A floor-standing loudspeaker with an amplified woofer or subwoofer. Pre-amp See Preamplifier Preamplifier An audio component that selects signal sources, and provides volume and tone compensation functions. There may be special gain stages for phono cartridge inputs. It has line-level outputs to drive a power amplifier. Normally a stereo device, its multichannel equivalent is a surround processor. Precedence Effect In sound localization, the fact that the first arriving sound (the direct sound) normally dominates our sense of direction. This allows us to correctly identify the direction of a source of sound in a reverberant space. See: Direct Sound, Haas Effect. Progressive Scan A video display that scans all lines sequentially in each pass. A Line Doubler can create a progressively scanned image from an interlaced scan signal. See: Line Doubler. Progressive spider A speaker's spider that provides increasing force (to restore the cone to the resting position) as it stretches Projector There are two ways to get an image on a screen. Shine light through an image forming element, or let light reflect from an image forming element. Both are very common. CRT projectors use an electron beam from behind and LCD devices rely on transmitted light to create the image, which is then communicated to a screen by lenses. Light valve (ILA), and D_ILA/LCOS devices rely on light reflecting off an image element, which is then focused on a screen using lenses. See: Light Valve, ILA, D-ILA, LCOS, CRT. Psychoacoustics The branch of acoustics that relates the physical dimensions of sound with the perceived dimensions - the relationships between what we measure and what we hear. Pulse-Code Modulation A straightforward, uncompressed, coding method in which analog signals are sampled at regular intervals and each sample is represented by a digital number representing the amplitude at that instant in time. Sampling is done at a frequency at least 2 times the highest frequency of interest, and the digital number must have a sufficient number of bits to capture and reconstruct the essential qualities of the audio signal (dynamic range, low distortion and noise, etc.). E.G. normal CD's are recorded using a sampling frequency of 44.1 kHz using a 16 bit digital number. See: Bit, Compression. Pure Tone A single frequency having a line spectrum. The periodic waveform is that of simple harmonic motion, a sinusoid. See: Spectrum. PVR Personal Video Recorder. A digital hard-drive video recorder (DVR) which, when combined with a program guide, can record one's personal favorite television programs. See: DVR.