By RALPH HODGES
GLOSSARY OF TECHNICAL TERMS--21
Load is the impedance presented to an audio component by whatever is connected to its output. The terms "load" or "load impedance" can therefore be used almost interchangeably with "input impedance," referring, of course, to the input of the component following the one in question. (In addition, the impedance of the interconnecting cables is also part of the total load "seen" by a component's outputs.) Amplifier specifications and test re ports frequently refer to "8-ohm loads." These are merely heavy-duty resistors connected to the outputs of an amplifier to simulate loudspeakers during tests on the amplifier.
Loudness is the subjective impression of a listener as to how intense a sound is. It differs from "volume," an arbitrary measure of the amount of electrical or acoustical power involved in a sound's production, because it is a nonlinear response to acoustical power that varies with frequency and, strictly, with the hearing of the individual. Therefore, turning up the volume control on an amplifier increases its power output by a measurable amount, but the correspond ing increase in loudness a given listener will perceive is not generally predictable.
Loudness compensation is an operating feature found in many amplifiers and receivers that compensates for the ear's insensitivity to the extremes of the audible frequency range at low listening levels. Music reproduced more softly that it would be heard "live" can sound thin and muted. Loudness compensation tries to make up for this by automatically boosting the bass and, frequently, the treble as the volume control is turned down. It begins to function at a certain low point in the rotation of the volume control, and it increases as the control is turned down. On some units the loudness compensation cannot be switched off, but it is preferable to have it activated by a separate switch.
Master has at least two meanings in audio. First, it designates an original recording, such as a master tape or master disc, or any one-of-a-kind version of a recording from which copies are made to sell or otherwise distribute. Second, it designates a "master" control-master volume or master gain-that simultaneously overrides the effects of a number of subsidiary controls. For example, a four-channel receiver might have separate level controls for all four channels, plus a single master volume control that raises and lowers the levels of all the Matrix is a word with several meanings in audio, but it is most familiar as the term for a family of four-channel recording/reproducing techniques employing (in most cases) only two trans mission channels. The original four channels are combined (encoded) into two channels in a special way and then recorded in that form. Upon playback, a special electronic processer (decoder) retrieves the original four channels by separating the signals according to certain specific clues (usually phase or amplitude differences) encoded into them at the time of recording.
Matrix systems were developed as one solution to the problem of recording four-channel pro grams on the two channels of phono discs. The two major systems at present are SQ, developed by CBS, and QS, designed by Sansui. (CD-4 is not considered a matrix system since it employs a 30 kHz "carrier" to embody the additional quadraphonic information.)
Mid-range -- roughly the four octaves between 500 and 8,000 Hz-is the range of frequencies to which the human ear is most sensitive and the range in which the greatest energy content of most music lies. The intermediate driver in a three way speaker system is called the mid range (and, infrequently, a "squawker"); however, it is seldom called upon to re produce the entire four-octave span.
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