Glossary of Audio Terminology

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Index | References




PAL (Phase Alternate Line)   The analog video standard used for television broadcast and composite video connections throughout Western Europe, except France, Hong Kong and the some of the Middle East. PAL signals encode the video as 625 horizontal lines of pixels.  (Only 576 of the lines are used for picture.  The rest are use for digital information such as VITC and Closed Captioning.)  The Lines are scanned in odd and even sets at 1 Field (1/2 frame) every 50th of a second (to work with the European  power standard of 50cps), resulting in am effective video frame rate of 25fps. PAL  is one of three main television standards throughout the world. See NTSC and SECAM

pan (panoramic) control A control found on mixers, used to "move," or pan the apparent position of a single sound channel between two outputs, usually "left," and "right," for stereo outputs. At one extreme of travel the sound source is heard from only one output; at the other extreme it is heard from the other output. In the middle, the sound is heard equally from each output, but is reduced in level by 3 dB relative to its original value. This guarantees that as the sound is panned from one side to the other, it maintains equal loudness (power) for all positions. Contrast with balance and crossfade controls.

parallel interface A parallel (as opposed to serial) interface transfers all bits in a word simultaneously  i.e. The parallel printer port on a personal computer. (A parallel port conforming to the quasi-standard called the Centronics Parallel Standard (there is no EIA standard). Originally a 36-pin connector, now more often a D-25 type connector.)  See also: serial interface.

parametric equalizer A multi-band variable equalizer offering control of all the "parameters" of the internal bandpass filter sections. These parameters being amplitude, center frequency and bandwidth. This allows the user not only to control the amplitude of each band, but also to shift the center frequency and to widen or narrow the affected area. Available with rotary and slide controls. Subcategories of parametric equalizers exist which allow control of center frequency but not bandwidth. For rotary control units the most used term is quasi-parametric. For units with slide controls the popular term is paragraphic. The frequency control may be continuously variable or switch selectable in steps. Cut-only parametric equalizers (with adjustable bandwidth or not) are called notch equalizers.

parity A redundant error detection method in which the total number of binary 1's (or 0's) is always made even or odd by setting the last bit or parity bit of a packet to the appropriate 1 or 0..

pascal Abbr. Pa A unit of pressure equal to one newton per square meter. [After Blaise Pascal.]

Pascal, Blaise (1623-1662) French philosopher and mathematician. Among his achievements are the invention of an adding machine and the development of the modern theory of probability.

passband The range of frequencies passed by an audio low-pass, high-pass or bandpass filter. Normally measured at the -3 dB point: the frequency point where the amplitude response is attenuated 3 dB (decibels) relative to the level of the main passband. For a bandpass filter two points are referenced: the upper and lower -3dB points. The -3dB point represents the frequency where the output power has been reduced by one-half. [Technical details: -3dB represents a multiplier of 0.707. If the voltage is reduced by 0.707, the current is also reduced by 0.707 (ohms law), and since power equals voltage-times-current, 0.707 times 0.707 equals 0.5, or half-power.]

passive crossover A loudspeaker crossover not requiring power for operation. Normally built into the loudspeaker cabinet. Passive crossovers do not require separate power amplifiers for each driver. See: active crossover

passive equalizer A variable equalizer requiring no power to operate. Consisting only of passive components (inductors, capacitors and resistors) passive equalizers have no AC line cord. Favored for their low noise performance (no active components to generate noise), high dynamic range (no active power supplies to limit voltage swing), extremely good reliability (passive components rarely break), and lack of RFI interference (no semiconductors to detect radio frequencies). Disliked for their cost (inductors are expensive), size (and bulky), weight (and heavy), hum susceptibility (and need careful shielding), and signal loss characteristic (passive equalizers always reduce the signal). Also inductors saturate easily with large low frequency signals, causing distortion. Rarely seen today, but historically they were used primarily for notching in permanent sound systems.

PBX (Private Branch Exchange) Private phone Switch used within a company that allows inter-company phone calls without using outside phone lines.

PC (personal computer) Original term coined by IBM to describe their first personal computers; now used to mean all IBM-compatible personal computers, or sometimes more generally used to mean any personal computer designed for individual use at home or in a business.


PC-DOSŪ (personal computer disk operating system) IBM's trademarked acronym for their PC operating system. If PC-DOS runs on an IBM compatible, it is then called MS-DOS.

PCI (peripheral component interconnect) Intel-designed high performance CPU interconnect strategy for  I/O subsystems. A 32- or 64-bit local-bus specification, characterized by being self-configuring, open, high-bandwidth and processor-independent - allowing for modular hardware design.

PCM (pulse code modulation) A conversion method in which digital words in a bit stream represent samples of analog information. The basis of most digital audio systems.

PCMCIA (Personal Computer Memory Card International Association) 1. The association and first name given to the standardized credit-card size packages (aka PC cards) for memory and I/O (modems, LAN cards, etc.) for computers, laptops, palmtops, etc. PC-Card, is now the preferred term. 2. Popularly believed to stand for People Can't Memorize Computer Interface Acronyms.

PDA (personal digital assistant) A small palmtop-like computer designed for specific tasks such as a pocket calculator. Other examples include personal electronic diaries, memo takers, communicators, web browsers, dictionary-translators, etc. Apple's Newton was the first PDA.

peaking response Term used to describe a bandpass shape when applied to program equalization.

peak program meter See: PPM

period Abbr. T, t 1. The period of a periodic function is the smallest time interval over which the function repeats itself. [For example, the period of a sine wave is the amount of time, T, it takes for the waveform to pass through 360 degrees. Also, it is the reciprocal of the frequency itself: i.e., T = 1/f.]

peripheral Equipment physically independent of, but which may interface to a computer or a controller.

PFL Abbreviation for pre fade listen, a term used on recording consoles and mixers, referring to a signal taken before the main channel fader. The significance is this signal is not affected by the fader postion. Normally used to monitor (via headphones) to an individual input (or a small group of inputs) without affecting the main outputs, particularly useful in that it allows listening to an input with its fader all the way down (off). In broadcast this function is often called cue, while recording or live-sound users may also refer to it as solo. Compare: AFL

phantom power The term given to the standardized scheme of providing power supply voltage to certain microphones using the same two lines as the balanced audio path. The internationl standard is IEC 268-15, derived from the original German standard DIN 45 596. It specifies three DC voltage levels of 48 volts, 24 volts and 12 volts, delivered through 6.8 k ohms, 1.2 k ohms, and 680 ohms matched resistors respectively, capable of delivering 10-15 ma. The design calls for both signal conductors to have the same DC potential. This allows the use of microphone connections either for microphones without built-in preamps, such as dynamic types, or for microphones with built-in preamps such as condenser and electret types.

phase lock loop A circuit for synchronizing a variable local oscillator with the phase of a transmitted signal. The circuit acts as a phase detector by comparing the frequency of a known oscillator with an incoming signal and then feeds back the output of the detector to keep the oscillator in phase with the incoming frequency.

phaser Also called a "phase shifter," this is an electronic device creating an effect similar to flanging, but not as pronounced. Based on phase shift (frequency dependent), rather than true signal delay (frequency independent), the phaser is much easier and cheaper to construct. Using a relatively simple narrow notch filter (all-pass filters also were used) and sweeping it up and down through some frequency range, then summing this output with the original input, creates the desired effect. Narrow notch filters are characterized by having sudden and rather extreme phase shifts just before and just after the deep notch. This generates the needed phase shifts for the ever-changing magnitude cancellations.

phase shift The fraction of a complete cycle elapsed as measured from a specified reference point and expressed as an angle. out of phase. In an un-synchronized or un-correlated way. See: polarity

phase delay A phase-shifted sine wave appears displaced in time from the input waveform. This displacement is called phase delay.

phon A unit of apparent loudness, equal in number to the intensity in decibels of a 1,000 Hz tone judged to be as loud as the sound being measured.

pi Symbol (Greek lower-case pi) 1. Mathematics. A transcendental number, approximately 3.14159, represented by the Greek lower-case pi symbol, that expresses the ratio of the circumference to the diameter of a circle and appears as a constant in many mathematical expressions. 2. Filters. Equal to 180 degrees or integral multiples thereof.

pico- Prefix for one trillionth (10E-12), abbreviated p.

pink noise Pink noise is a random noise source characterized by a flat amplitude response per octave band of frequency (or any constant percentage bandwidth), i.e., it has equal energy, or constant power, per octave. Pink noise is created by passing white noise through a filter having a 3 dB/octave roll-off rate. See white noise discussion for details. Due to this roll-off, pink noise sounds less bright and richer in low frequencies than white noise. Since pink noise has the same energy in each 1/3-octave band, it is the preferred sound source for many acoustical measurements due to the critical band concept of human hearing.

pixel (picture element) The smallest element on a display surface, like a video screen, that can be assigned independent characteristics (color and brightness).

PLA (programmable logic array) A programmable logic device in which both the AND & OR arrays are programmable.

PLD (programmable logic device) The generic name for an integrated circuit offering a vast array of logic function building blocks that the circuit designer defines (programs) to interconnect for specific applications.

polarity A signal's electromechanical potential with respect to a reference potential. For example, if a loudspeaker cone moves forward when a positive voltage is applied between its red and black terminals, then it is said to have a positive polarity. A microphone has positive polarity if a positive pressure on its diaphragm results in a positive output voltage.

POP (Point of Presence) The location of office where a digital line from an Inter-Exchange Carrier (IDX) connects to the Local Exchange Carrier (LEC).

Port any of the connections to a computer that allow the transfer of data.

POTS Acronym for plain-old telephone system. The normal single line basic telephone service.

PowerPC A super powerful RISC processor PC jointly developed by IBM, Apple and Motorola, designed to run any PC operating system (MS-DOS, UNIX, Windows, OS/2, Mac OS. etc.). Featured in Apple's line of "PowerMac" computers.

PPM (peak program meter) An audio meter originally developed in Europe to accurately measure and display peak audio signals (as opposed to average audio signals; see VU meter). The PPM augments the VU meter and it is normal to find both in modern recording studios. The PPM is particularly valuable for digital audio recording or signal processing due to the critical monitoring required to prevent exceeding 0 dBFS. There are several Europena PPM specifications, but no one universal standard; although the German DIN specification 45406 functions somewhat as a de facto standard. An interesting aspect of PPM design is that rather than respond instantaneously to peaks, they require a finite integration time so that only peaks wide enough to be audible are displayed. DIN 45406 translates this into a response that is 1 dB down from steady-state for a 10 ms tone burst, and 4 dB down for a 3 ms tone burst (this is consistent with the other commonly seen specification of 2 dB down for a 5 ms burst -- both requirements are satisfied by an attack time constant of 1.7 ms (BBC requirement is 2.5 ms). The specified decay rate of 1.5 seconds to a -20 dB level can be met with a 650 ms time constant.

precedence effect See: Haas Effect

pre-emphasis A high-frequency boost used during recording, followed by de-emphasis during playback, designed to improve signal-to-noise performance.

print-through The name for the magnetic tape recording phenomena where the act of layering, or winding layer upon layer of tape causes the flux from one layer to magnetize the adjacent layer, thus printing through from one layer onto another layer. Also called crosstalk or interlayer transfer. The most vulnerable parts of the magnetic tape are the blank spots, particularly leaders and spaces between material that happen to occur adjacent to loud passages.

PROM (programmable read-only memory) A memory device whose contents can be electrically programmed (once) by the designer.

protocol A specific set of rules, procedures or conventions relating to format and timing of data transmission between two devices. A standard procedure that two data devices must accept and use to be able to understand each other.  The protocol controls how the entire network communicates (how data packets are assembled for transmission and how received packets are interpreted).

psychoacoustics The scientific study of the perception of sound.

PTSN (public switched telephone network) the public telephone system in the US. See also POTS.

PWM (pulse width modulation) A conversion method in which the widths of pulses in a pulse train represent the analog information.

Px64 The ITU-T's international video standard which provides a standard algorithm for video compression and decompression.  Formally known a H.261.


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