What exactly are the differences among different classes of tape, and among brands offering the same class?

A series of laboratory and listening tests, just concluded, provides some new insights into this subject. The full results of these tests, in which I was involved, will be published in the May issue of the magazine Modern Recording. With their permission, I can give you a sneak-preview of the highlights.

Cassette samples from seven manufacturers were tested for key performance aspects. The samples included the premium offerings in standard or normal-bias tapes, high-bias tapes (chromium-dioxide or "equivalents"), and the new metal-particle tapes, which take the highest bias. Corresponding equalization values were 120 microseconds for the normal-bias tapes, and 70 microseconds for all the others. The seven brands tested were Ampex, Fuji, Maxell, Memorex, Scotch, and TDK.

At the risk of oversimplifying, here is what we found. For frequency response at normal recording levels, there were only slight differences between various brands of any class of tape. There was perhaps a bit more difference between one class as a whole and another class. That is, the high-bias tapes had a slightly wider overall frequency span than did the normal-bias tapes, while the metal tapes had the widest frequency range of all. But every tape tested responded at least from 25 Hz to 20,000Hz.

At higher recording levels, no great differences could be discerned between normal-bias and high-bias tapes. Metal tape, however, did noticeably better in this test, demonstrating an ability to record greater signal levels, especially in the highs.

While signal-to-noise ratios were about equally good for both normal-bias and high-bias tapes, they were much better for metal tapes, reaching levels greater than 60db without Dolby, and at least 70db with the Dolby switched on.

Distortion was a standoff between normal-bias and high-bias tapes. It was significantly lower with metal tape.

It was impossible to single out a clear winner among either the normal-bias or the high-bias tapes. If you read the full report in Modern Recording you will see why in terms of the specific test results. You also may see why some tapes seem more suited than others for specific recording chores, although on final balance, all were quite good. Among the metal tapes, Fuji did score highest in more tests than any other brand. Again, however, differences between it and the others were truly small, as were the difference among those other metal brands themselves.

High-bias oxides, were not "all that great" in direct comparison. Their most audible benefit seemed to be a slightly better definition of complex orchestral passages, although even on this point there was no universal agreement among the listening panel.

The one thing that did emerge with certainty from the tests is that the metal tapes do offer greater recording headroom, mostly for the highs but with some improvement generally along the entire frequency spectrum. They also permit you to record at a more favorable signal-to-noise ratio, and with lower distortion. But to realize the benefits of metal tape, you must use it only on a deck that is competently designed to handle it. Otherwise, it's a waste.

You can, of course, play a recorded metal tape on any deck (including car tape models) that has the 70-microsecond equalization option. Even without this feature, the metal tapes can be played, although you may want to turn down the treble tone control. FEEDBACK

CORRECTION: The answer to a question on wire thicknesses (in Show, Feb. 24) was given incorrectly due to an error in the retyping. The second paragraph should have explained that four No. 22 wires provide the same thickness as one No. 16 wire. Similarly, four No. 20 wires would equal one No. 14 wire.