For many years, there were just two basic types of cassettes: those using iron oxide as magnetic particles, usually called ferric tapes, and those using chromium oxide, called chrome tapes. Ferric tapes are cheaper, but chrome tapes tend to have a brighter sound with more clearly defined high frequencies and a quieter background. However, many brands of ferric tapes have recently been upgraded, using smaller and more evenly distributed magnetic particles to improve their response at the high end. (The small grain permits more sonic detail to be recorded, just as fine-grain photographic film yields sharper detail in pictures.)

These improved ferric tapes offer a well-balanced and musically satisfying frequency response with notable smoothness of sound, and many listeners find them entirely adequate. Outstanding examples are BASF Professional I, TDK-AD, Fuji FX-1, Sony SHF, Maxell UDXL-1 and Scotch Master I. They all sell for about $4 to $5 for a one-hour cassette (C-60) and are often available at discount. Among the slightly higher-priced chrome cassettes, BASF Professional II is outstanding for added clarity of highs, exact definition of musical details and low background noise.

Quite similar to chrome cassettes in their bright and punchy sound are the so-called chrome-equivalent tapes, sometimes also called high-bias tapes. While they contain no chrome, they achieve close sonic resemblance to chrome tapes by using ferric particles chemically bonded with cobalt. The result of this sophisticated approach yields excellent sound, as witness TDK's SA, Maxell's UDXL-II, Sony's EHF and Fuji's FX-II. Along with the pure chrome tape, these high-bias chrome-equivalent tapes rank among the favorites of audio fans with good equipment who are seriously concerned with fidelity. Prices average about 50 cents more than for ferric cassettes.

To get the best possible results from different kinds of cassettes, you must adjust the circuits of your tape recorder to match the requirements of the tape. That's why the better tape decks have selector switches by which the recorder can be optimized for the kind of tape you choose. If your machine has no such switch, and some of the less expensive portables do not, probably it has been factory adjusted for ferric tapes, and you had better stick with them.

In addition to the basic tape types already mentioned, two other formulations have lately attracted attention. Among these are ferrichrome tapes, in which a thin layer of chrome is superimposed on a ferric substrate in an effort to combine the virtues of both materials. The chrome gives clarity to the highs while the ferric material adds strength to the bass.