Highway high-fidelity just keeps truckin' along picking up new riders all the time.

Of all the segments within the consumer electronics industry, car stereo suffered the least slowdown in 1979. Auto sound is now a billion-dollar-a-year business, with an annual growth rate of 15 to 20 percent.

In just five years, car stereo products have evolved from the industry's laughingstock into equipment that must be taken seriously. Auto sound even scored a major technical first with its microprocessor-controlled, quartz-locked electronic tuning systems -- just now being introduced in home receivers by the likes of Sony and Radio Shack.

During the same period, many millions of people have decided to hold onto their cars longer and sealed that commitment by upgrading their auto sound systems.

Growing consumer awareness of audio alternatives is also making better shoppers of new car buyers. Rather than routinely buying a factory-installed radio, they're buying an after-market system with much better specifications and features at virtually the same price of a factory unit.

Mix and match a basic radio-tape cassette player with power boosters, equalizers and multi-speaker systems, and create an environment in the car akin to nestling inside the world's largest set of headphones.

Careful do-it-yourself types can install a car stero on a weekend, but consult first with a knowledgeable dealer. It's foolish to invest in expensive speakers, unless you have sufficient amplifier power to bring out the best the woofers can offer. And too much power will blow out speakers designed for a low-end (one or two watt per channel) car radio.

Then too, many radio cassette combos simply will not fit dashboard cutouts -- especially the smaller spaces alloted in foreign cars. Same goes for speakers: there must be sufficient clearance in the door cavities or in the rear deck's metal substructure. Some car components come with oddball jacks and plugs that only fit other pieces made by the same manufacturer.

Choices are increasing. At the Winter Consumer Electronics Show in Las Vegas, both Kenwood and Altec-Lansing jumped into auto stereo exotica. And virtually every manufacturer was pushing high end receivers with advanced features: high power specifications, Dolby noise reduction, digital readout of station and time, search-and-seek channel tuning, station memories, automatic tape reverse, song-repeat capability, improved tape heads, multiple playing speeds, even TV audio bands.

Major features on the 13-model Kenwood line include ABSS, an automatic broadcasting sensor system that adapts the tuner to changing signal conditions; and a second FM tuning aid, ANRC, an automatic noise reduction circuit. In weak signal areas, ANRC blends the high-end frequencies into a monaural signal to reduce noise, and will cue a cassette if the signal becomes weak. Some Kenwood cassette models also have special circuitry that searches for gaps between recordings, so the user can program certain cuts. (Sharp and Alpine models also offer this.)

For those seeking a higher powered, all-in-one receiver, Craig is offering the new T687 model with alloy heads that can handle metal particle tape. It's claimed they are much harder and longer lasting than the typical permalloy heads. You'll also find this new tape head on Concord's HPL-505 and the Fujitsu Ten model DP-644.