By RALPH HODGES
GLOSSARY OF TECHNICAL TERMS- 10
Direct-coupled usually describes an amplifier whose power-output transistors are connected directly to the speaker system, without any intervening capacitors or transformers. In a stricter technical sense, it can also refer to an amplifier that is fully direct-coupled internally: that is, with no capacitors or transformers anywhere in the signal path from input to output. Direct coupling generally results in less nonlinear phase shift and a frequency response down to d.c. (0 Hz). The technique is being used more and more in modern amplifiers and receivers.
Discrete, meaning "separate" or "individually distinct," designates a four-channel system or medium in which the four channels are retained as electrically separate entities all the way from the recording studio to the playback speaker systems. The term is often used in opposition to "matrix," a technique in which the four channels are temporarily combined into two for recording purposes. (A discrete system is theoretically capable of perfect separation between channels, while current matrix systems are limited in this respect.) All the completely discrete program sources currently available are tape systems, such as open-reel four-channel tapes and Q-8 eight-track cartridges. The CD-4 four-channel disc system is described as discrete because it offers the audible equivalent in separation be tween channels. However, purists point out that since CD-4 employs matrix processing during recording and reproduction, it does not fall within the strict definition of a discrete system.
Dispersion, as a rule, refers to the directional properties of a speaker sys tem-the solid angle over which it radiates its output at various frequencies. This is particularly significant for high frequencies, which a conventional speaker may project straight forward in a relatively tight "beam" unless steps are taken in the design to prevent this. Wide dispersion speakers are often credited with a "spacious" sound, probably because of the wealth of room reflections they create. On the other hand, some listeners find that speakers with narrower dispersion produce a more precise stereo image.
A second meaning for "dispersion" comes from the magnetic-tape industry, where the word describes the density and uniformity with which oxide particles are spread over a tape's surface.
Distortion, in the broadest audio-reproduction sense, is any change in-or addition to-the original sound (usually excluding noise and hum). It can be introduced by any component in the re production chain, from the recording microphone to the playback speaker sys tem. The distortions that are purely electrical in origin-especially harmonic and intermodulation ( IM) distortion--usually receive the most attention in audio-component specification sheets; they will be discussed under their proper separate headings in future columns. Other forms of distortion include phase, amplitude, and frequency-response distortion, as well as more complex distortions occurring when the mechanical, electrical, or magnetic limitations of recording and reproduction devices are exceeded.
These last types, often called "overload" or "overdrive" distortion, may have such causes as phono-cartridge mis-tracking, amplifier "clipping," or magnetic-tape saturation.
When present in audible amounts, distortion can obscure the clarity of reproduced sound and add spurious, some times annoying, sonic qualities. The amount of distortion is usually expressed as a certain percentage of the desired signal, with 0.5 percent or less being typical of high-fidelity amplifiers, for example. The percentage that is audible in any given circumstance depends on the type of distortion as well as many other factors.
Also see:
TECHNICAL TALK--What Is Noise?
NEW PRODUCTS--A roundup of the latest in high-fidelity equipment