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SOUND; New Tapes Strive For CD Standards
By Hans Fantel
Published: Sunday, April 16, 1989
No tape recorder can be any better than the tape running in it. No matter what the capabilities of the machine, the tape itself is the carrier of the recorded sound and affects such vital factors as frequency response, the level of background noise (tape hiss) and the dynamic range. Lately, these matters, often taken for granted, have received lots of renewed attention.
The past several years have seen an effort to upgrade cassette recorders to bring them more closely in line with the new sonic standards set by CD's. For example, almost half of all the better cassette decks now being made include HX-Pro circuits. These circuits widen the dynamic range of the recorder to approach, though not equal, that of a typical CD, making it easier to copy CD's onto tape. Moreover, the frequency response of many tape recorders has been extended to capture more of the digital original during such copying.
These engineering changes have left the capabilities of the tape itself lagging behind those of the better recorders - a challenge now being addressed by many tape producers. Among them, TDK and Maxell, two of the best-known brands, have come up with new tape types specifically formulated to take full advantage of today's improved cassette recorders.
On average, a CD has about 10 decibels greater dynamic range than cassettes could accommodate in the past. So, to permit unconstrained copying of CD's, those extra decibels somehow had to be squeezed onto the magnetic layer. In other words, the dynamic range of the tape had to be enlarged.
Dynamic range is the span between the loudest and softest sounds the tape can retain. It is also important for this range to be uniform at all frequencies. For example, some tape types may have a wide dynamic range for the middle frequencies but skimp on highs when the music gets loud. Conversely, low bass notes, played very softly, may be buried in the residual background noise and thus become lost to the ear.
In concocting their new magnetic mix, tape chemists and engineers therefore tackled the problem of dynamics at both ends: They increased the relative high-frequency output (relative to the rest of the sonic spectrum) at the top of the loudness scale; and they lowered residual noise level to allow very soft sounds to be heard clearly. That way, the overall range was expanded to the point where - on a good machine - all but the most exceptional CD's can now be copied onto cassette tape without the need for constantly adjusting the level of the recording to avoid overloading the tape or losing the soft passages.
For example, Maxell's XLII-S top-ranking Type II (oxide) formulation attains a dynamic range of 56 decibels, and TDK's SA-X tape surpasses even that remarkable figure to reach 59.1 decibels. This is not to say that the copies made with these tapes will be indistinguishable from the original - that's impossible without using digital copying methods, which are not yet widely available in this country.
But these new top-grade tapes allow audio fans to copy CD's easily and effectively with only slight sonic loss. Tape manufacturers tend to be rather close-mouthed about the details of their trade, but during an informal discussion at a TDK-sponsored seminar, it was disclosed that, aside from modifying the magnetic material itself, the orientation of the microscopic particles had been re-arranged.
The new particle layout allows greater packing density; i.e., more particles can be crowded into a given area on the tape. Since the magnetic force of the particles is cumulative, the greater number of magnetic units adds up to a greater magnetic force - hence higher output and dynamic range.
Wanting to capture the striking limpidity of the best CD's as well as their dynamics, both Maxell and TDK became concerned about a hitherto neglected aspect of tape performance known as modulation noise. This is caused by the plastic cassette housing vibrating as the tape rolls within it, which makes the sound slightly muddy.
To cope with these infinitesimal jitters of the cassette, both Maxell and TDK developed new cassette housings whose materials and construction make them less vibration-prone than before. In the case of TDK, the two molded halves of the housing consist of materials with different vibrational periods. So when the two cassette halves are bonded together, their dissimilar vibratory motions cancel each other because one half vibrates out of phase with the other. The result is a measurable reduction of modulation noise with a corresponding gain in sonic clarity.
A C-90 cassette of Maxell's XLII-S lists at $4.39 and TDK's SA-X at $3.50, though both are often sold at discount. Both are Type II tapes, which means that they must be used with the tape selector switch on the recorder in the high-bias position.
Intensive development work has also been done on other tape types. The less expensive, low-bias Type I tapes as well as the pure-metal Type IV tapes have also been upgraded. Yet among the variety of tapes now offered, the two new entries discussed here represent likely choices for serious audiophiles. They stand up admirably to even the most demanding recording tasks.
A version of this article appeared in print on Sunday, April 16, 1989, on section 2 page 25 of the New York edition.
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