Anyone contemplating the purchase of a cassette recorder these days might well wonder about a very wide difference in the prices being asked for different models that, on the basis of performance claims, all seem to offer pretty much the same general level of audio competence.

There are models that cost less than $500, and there are others priced higher than $1000. Yet if you study the specifications, you will not discern any really significant difference in these price classes as regards such basic criteria as frequency response, distortion, signal-to-noise ratio, wow-and-flutter , and recording signal headroom.

What's more you will notice many similarities among these differently priced models. They all include Dolby noise-reduction (or the ANRS equivalent), switching to adjust the recorder for handling different kinds of tape, reliable signal-level indicators, the normal complement of inputs, outputs and level controls.

So what does the higher price tag get you? One fairly universal feature in the kind of tape transport system that operate with "feather-touch" buttons in a solenoid "logic-control" system. In contrast to the lower-cost mechanical key system, the fancier version makes operation of the dock a little easier and faster. It permits "fast-buttoning," whereby you can change instantly from one transport mode to another without the need to press the stop button (which is how decks operate).

Beyond this embellishment, the options available in the high-priced cassette models vary, depending on what their manufactures deem importance enough to justify a major design effort that is in turn calculated to justify the higher price. A unique metering system, or some form of microprocessing, or an elaborate bias adjustment may be offered. The most novel of these is found in the new Hitachi D-5500, which contains a built-in "microcomputer" that automatically sets bias, equalization and recording levels for different kinds of tape and has a "memory" circuit that stores the data and makes it available at the press of a button.

If you care to spend the premium prices such cassette recorders command, you can enjoy top-grade cassette sound plus the particular kind of sopthiscated features one or another model offers. However, its also is possible to get top-quality cassette sound at far lower cost, albet with-out the super-fast-acting transport controls or some of the other special emballishments. Remember, the special features in themselves, while they can make a recorder easier or more fun to operate do not in themselves contribute to better sound.

A case in point, which indeed strikes me as the most significant one to date, is the new Harman-Kardon hk-3500, which lists for$170.

In our lab tests, this model had a frequency response using standard low-noise tape of 30 Hr to 10,000 Hz. Signal-to-noise, with Dolby, came to 67 dB. Harmonic distortion was well below 1 percent, and recording headroom was quite ample at plus-6 dB. The musical sound of this machine-thanks to Harman-Kardon's avowed use of "wideband" circuitry is second to none, regardless of price.

The less-than-$500 price of the hk-3500 is of course made possible by the use of a mechanical transport rather than the more sophisticated kind. Even so, the machine runs very smoothly and has a wow-and-flutter of only 04 percent WRMS, which rivals that of costlier models and is audibly insignificant.

The metering in the hk-3500 is conventional but accurte, and peak levels are clearly shown. For tape selection, there are separate swithces for bias and for equalization, plus a bias "trim" that may be used in conjuction with a built-in test tone while the correct reading is obtained on the deck's own meters.

It also is possible to calibrate the Dolby circuit using another built-in test tone and referring to the meters.

Other features that are surprising in view of the deck's cost are separate heads for records and play, input, mixing of line and microphone aignals, a record-mute option and even a fine-speed adjustment to "tune" cassette playback to a given musical pitch for special purposes.

Maybe the hK-3500 is the expection to the rule, but it certainly seems an exceptional value in cassette recorders today.