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