HOW IS your image these days? That is, the image your home stereo system is supposed to create. Devices to improve it are now offered by Carver Corp., Sound Concepts and Omnisonix. A fourth model is expected soon from Dynaco, and a studio system developed by JVC may be offered later for consumer use. Reportedly, several other companies will be marketing similar devices this year.

The image devices are designed to restore a more convincing sense of stereo space both laterally and in terms of front-to-rear depth than is possible with conventional loudspeakers. The aural effect, to put it perhaps over-simply, is more like listening with headphones, whereby the sound seems to exist well beyond the physical domain of the devices producing it. In manipulating the normal stereo signal in a playback system on its way to the loudspeakers, the image device effectively expands the apparent sound field set up by the speakers but it does not, as a concomitant, degrade the "center image" or create a "hole in the middle" between the two stereo speakers.

This is a neat trick, and it does work. The Carver, Sound Concepts and Omnisonix units are all capable of doing the job, but there are differences among them that are important to potential buyers.

At $200, the Omnisonix is the lowest priced. It also is the easiest to connect into a stereo system. All these devices are intended for connection into the tape monitor loop normally found on today's receivers and amplifiers, but only the Omnnisonix replaces that facility with its own tape-monitor jacks and switch. To use the others, you must disconnect the existing tape-monitor function and reconnect it with the image device. Some, but not all, receivers or amps have an external signal-processing loop that can be used. Alternately, if you want to keep a tape recorder connected in the normal way, you will have to purchase an additional accessory known as a "tape monitor loop extender."

The Omnisonix also is the easiest to ue, but this is a mixed blessing. It has no operating controls, and so its image-enhancement is fixed. The other two units have operator controls that vary the image enhancement according to source materials, speaker placement and your own listening position. This last factor is critical in that the most apparent image improvement is perceived from a relatively limited listening area equidistant from both speakers. In this regard, the Sound Concepts unit provides a fillip not found on the others -- it comes with extension cables that permit you to adjust it while you listen from your chosen spot in the room. This unit costs $229. The Carver C-9 unit costs $279, and is also incorporated in an elaborate preamp-control unit -- the C-4000 priced at $900. i

Listeners disagree in their reactions to the three units. The Carver and the Sound Concepts devices seem to do the same things to reproduced music -- all good. The Omnisonix lends an apparent increase in high-frequency volume to some musical passages, which some listeners found agreeable. Others felt the same effect could be had by turning up the volume control. We tried this, but the effect was not quite the same.

None of these devices will filter out noise in a program source. On the contrary, they tend to emphasize noise such as record-surface ticks, or the hiss from older tapes or from some FM broadcasts. To get the most from any of these units, really clean source material is required.

The image devices do their job without the need for extra speakers or a second amplifier, but their maximum effectiveness is restricted to a fairly small listening area in front of, and equidistant from, the two stereo speakers. In this sense, it becomes a kind of "private trip" for one or two listeners. Whether or not that trip is necessary can best be decided by trying it at a hi-fi dealer.