Rackmount refers to equipment designed to meet the EIA
standard for equipment cabinets or racks. The front face is
usual 19" wide thus the term " 19" rackmount ".
radian Mathematics. A unit of angular measure equal
to the angle subtended at the center
of a circle by an arc equal in length to the radius of the circle,
approximately 57°17'44.6 Filters. Frequency is measured
in radians/second. One cycle (360°) equals 2 pi
Radio Spectrum see
RAM (random access memory) A
memory device that may be accessed independent of the previous call.
RAM is used in computers to store programs and data need to be
accessed quickly. Due to it's electronic format ( unlike the
mechanical portions of hard disc and optical drives ) RAM responds
very quickly to request for reading or writing data. Unlike ROM, RAM
is completely erased when the power is removed form the chip. This
type of memory is thus sometimes referred to as being volatile.
rarefaction 1. A decrease in density
and pressure in a medium, such as air, caused by the passage of
a sound wave. 2. The region in which this occurs.
RCA jack (aka phono jack) The Radio Corporation of
America (RCA) originally developed this type of pin connector for
internal chassis connections in radios and televisions during the
'30s. It became popular for use in the cables that connected phonograph
cartridges to preamplifiers because it was inexpensive and easily
fitted to the rather small diameter shielded cables used for the
cartridge leads (then they were mono cartridges so single conductor
shielded cables were adequate). Now the standard for use in line
level consumer audio and project studio sound equipment, and most
recently to interconnect composite video signals.
R-DAT or DAT (rotary head digital
audio tape recorder ) A digital audio recorder utilizing
a magnetic tape cassette system similar to that of a video recorder.
real-time operation What is perceived to be instantaneous
to a user (or more technically, processing which completes in a
specific time allotment).
reconstruction filter A low-pass filter used at the output
of digital audio processors (following the DAC)
to remove (or at least greatly attenuate) any aliasing
products (image spectra present at multiples of the sampling frequency).
Academy, The The organization formerly known as NARAS
(National Academy of Recording Arts and Sciences).
recording console See: mixer
Resolution The sharpness or clarity of a video display
device. Measured as the number of Pixels (HxV) displayed.
RF (radio frequency) Radio frequency
(abbreviated RF, rf, or r.f.) is a term that refers to alternating
current (AC) having characteristics such that, if the current is
input to an antenna,
electromagnetic (EM) field is generated suitable for
broadcasting and/or communications. These frequencies cover a
significant portion of the electromagnetic radiation spectrum,
extending from nine kilohertz (9
kHz), the lowest
allocated wireless communications frequency (it's within the range
of human hearing), to thousands of gigahertz (GHz).
RISC (reduced instruction set computer)
A computer design that achieves high performance by doing the
most common computer operations very quickly, utilizing a high speed
processing technology that uses a far simpler set of operating commands.
Primarily found in printers and the Motorola PowerPC
chip. The alternative to CISC (complex instruction set
computing), the original way of doing computing.
RJ (Registered Jacks) As in the RJ-12 modular
ROM (read-only memory) A memory from which data,
after initial storage, may only be read out, but new data cannot
be written in. The normal audio CD is an example of a read-only
root mean square Abbr. rms,
RMS Mathematics. The square root of the average of the
squares of a group of numbers. A useful and more meaningful way
of averaging a group of numbers.
rotary equalizer A multi-band variable equalizer using rotary
controls as the amplitude adjustable elements. Both active and passive
designs exist with rotary controls.
Digital: A device that bridges and internal digital network to and
external network. May also be used to describe a device that
translates between two different protocols of digital
communications. For example the router that bridges a Ethernet
network to a T1 line. 2. Analog: An audio device used to selectively
assign any input to any output. Does not usually including the ability
to add inputs together. In this way, one input could go to all outputs,
but all inputs could not go to just one output. Typically, level controls are provided on all
inputs and outputs; balanced and unbalanced designs exist. More
elaborate designs including the ability to mix inputs together are
Just to make this totally confusing, some analog matrix-mixers such
as the Peavey Media Matrix perform all routing functions in a
digital domain even though all inputs and outputs are analog audio.
RS (Recommended Standard) As in RS-232
serial interface standard, et al.
RS-232 The standard serial interface
(EIA/TIA-232-E) used on most personal computers. A
format widely supported for bi-directional data transfer at low to
moderate rates ( typically .3 to 190.2Kbps). The most common interface method used to connect
personal computers with peripheral hardware and instruments. Use
is restricted to one peripheral at a time and short distances. The
standard originally called for DB-25 connectors,
but now allows the smaller DB-9 version.
RS-422 The standard adopted in 1978
by the Electronics Industry Association
as EIA-422-A, Electrical characteristics of balanced voltage
digital interface circuits. A universal balanced
line twisted-pair standard for all long distance (~1000 m, or
~3300 ft) computer interconnections, daisy-chain style.
RS-485 The standard describing the electrical characteristics
of a balanced interface used as a bus for master/slave operation.
Allows up to 32 users to bridge onto the line (as opposed
to RS-422's need to daisy-chain the interconnections).
RS-490 The standard adopted in 1981 by the EIA
entitled Standard Test Methods of Measurement for Audio Amplifiers.
The power amp testing standard for consumer products.