Glossary of Audio Terminology

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Index | References




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 5717'44.6  Filters. Frequency is measured in radians/second. One cycle (360) equals 2 pi radians.

Radio Spectrum  see Electromagnetic Radiation Spectrum.

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).

Recording 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, an electromagnetic (EM) field is generated suitable for wireless 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 telephone jacks.

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 system.

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.

Router 1. 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 called matrix-mixers.  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.



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