Invention, or at least innovation, has long been a hall mark of the audio field. Right now we're witnessing a remarkable trend -- that of the "one-brand system" -- supported by more than two dozen well-known names in component stereo hi-fi, with the number likely to increase. This type of system, typically installed in a vertical open- shelf housing or rack mount, appealed to stereo buyers who wanted to let it all hang out in bold, studio-like fashion. The display of closely packed audio gear with its panoply of knobs, switches, dials and meters was a source of pride to its owner. And since the upright housing took less floor space than a horizontally spread-out installation, it also appealed to those with limited floor space. The speakers still occupied their own spots apart from the vertical setup. Whatever its original reason, this idea is expected to stimulate stereo sales among consumers who aren't steeped in the jargon that was part of buying the "mix-and-match" audio system. The one-brand system obviates many of the decisions formerly involved in buying high-quality audio components -- matching of components, choice of turntable and so on. From a cosmetic standpoint, the one-brand system looks uniform: The parts are matched visually as well as electronically. Buying it all from the same source also means the consumer need cope with only one dealer if service problems arise. And a dealer is more likely to offer a discount when selling several components at once than when selling one at a time. Above all, the one-brand system offers stereo performance that -- depending on the system chosen -- can rival or top that of the older mix-and-match system. This brings us to a major point and a little recent history. The kind of system we're talking about is nothing like the system typically found in the console radio- phonograph of some years ago. In those filigreed monsters, there was a series of compromises known as "interlocking neuroses." The speakers in those systems were housed in the same cabinet as the record player and electronics. One problem stemming from this design was the inadequate baffling of the speakers for full bass response. Another was the danger of feedback from speakers to record players. Indeed, if the speakers had been designed for full bass, feedback probably would have resulted. Here we see two negative features combining to create a "lesser evil" or "negative advantage." With bass response deliberately restricted, it became useful to restrict the extreme high-frequency response, too, in the interest of a "balanced spectrum." The amount of propaganda launched to justify this frequency restriction in "psychoacoustic" terms -- when it was basically a commercial expedient -- is amazing. This approach was used not only on the speakers, but also on the amplifier, which obviously would not be required to furnish the full audio range. And with a restricted response, there was no need to offer a really high- quality pickup cartridge, which in turn meant the tone-arm could be skimped on. And since the deep bass was missing, the turntable itself could have an amount of low-frequency noise (rumble) that would be intolerable in a wide-range playback system. This "interlocking neuroses" approach applied first to pre-stereo consoles. When stereo came along, it also was tried for the two channels. But a new problem emerged: The two speakers in the single cabinet couldn't possibly be wide enough apart to produce a good stereo effect -- except for someone sitting very close to the system. A idea grew more popular. If the component approach began displacing the older one-piece console approach, why is the one-brand system coming back? There are two main reasons. One is that the kind of involvement with specifications and technicana that typified the hi-fi buyer a few years ago simply doesn't apply to the entire population. The kind of buyer who's now ready to invest in high-quality sound for the home is not necessarily a hard-core audiophile, but just someone who wants good value for money spent -- ready to buy hi-fi stereo despite a lack of specialized understanding. The emphasis is on the musical performance of the system as a whole. The second reason one-brand system is coming into its own is that manufacturers are getting better at doing more things well. At one time, Company A was known mainly, or only, for its amplifiers; Company B for its turntable; Company C for its tape decks. In the past decade or so, as a result of industrial expansion, mergers and acquisitions, this picture has changed. At last count, the roster of companies capable of offering all, or most, of the components needed for a complete stereo system includes: Aiwa, Akai, Bang & Olufsen, Fisher, Harman-Kardon, Hitachi, JVC, Kenwood, KLH, Marantz, Mitsubishi, Nikko, Onkyo, Optonica, Panasonic, Pioneer, Revox, Rotel, SAE, Sansui, Sanyo, Scott, Sharp, Sony, Technics, Toshiba and Yamaha. The list is expected to grow. Prices for systems offered by these firms range from a few hundred to a few thousand dollars, depending on performance, features and the number of components. For instance, the Fisher System 2100 for $699. It includes a tuner, a control amplifier rated for 30 watts per channel, a turntable, cassette recorder and two speaker systems. At a higher price level, there's the Harman-Kardon 700 series. For a little under $1,500, you get a digital tuner, separate preamp, 65-watts-per channel power amp, turntable and equipment cabinet. Speakers, which are not made by H-K, remain the buyer's option -- something that the companies who specialize in speakers are hardly unhappy about. That the one-brand system is also aimed at affluent and/or more technically stimulated buyers is seen in the Revox lineup, which includes a linear-tracking turntable, a receiver that costs $2,899, tape decks ranging up to $3,000, speakers up to $2,300 and a $365 rack-mount. One-brand system development is seen as heralding new twists to the marketing, advertising and even the instruction manuals supplied with equipment. Specifications as such will become more the shop-talk among insiders; their significance in actual sound will be emphasized to the consumer. While the traditional audio specialty shop will continue to cater to the mix-and-match aficionado, more equipment will be showing up in department stores and discount houses. Many of the things taken for granted in the past by manufacturers in their communications with the people buying their products will have to be rethought and rephrased. The fact that someone is willing to spend $2,000 for a stereo system no longer implies that he or she also knows what such terms as "impedence" or "tinning the lead-ends" mean. If they're not quite "selling the sizzle," at least they won't be bending your ear with the specifications of the steer.