Behind The Scenes (Mar. 1974)

TEN YEARS AGO Phillips of Holland introduced what they called the "compact cassette." In essence it was a miniature reel-to-reel tape system enclosed in a handy-sized plastic cassette. With a tape width of less than an eighth of an inch, and operating at a snail-paced 1 7/8 ips, the frequency response and signal-to-noise ratio were quite restricted, but deemed adequate for its intended purpose .. . that of a convenient format for dictation and sonic "note-taking." Incorporated into pocket-sized battery operated portable recorders, the cassette system soon caught the fancy of millions of people. As with any tape recording system, it was inevitable that the cassette would inspire experimentation as to its feasibility as a storage medium for music. In spite of the pitiful quality of those early monophonic recordings, it was obvious that quite a few people felt that the cassette had great potential as a vehicle for commercially produced recordings. A great deal of money, time and technology was lavished on the cassette to make it a viable music playback system, and the rest is history...

Today, the devotee of cassettes has a highly sophisticated system at his disposal. There are hundreds of models of cassette recorders, and from $150 units on up to $1100, Dolby B-Type noise reduction is virtually standard. Even the modestly-priced recorders have quite respectable motion performance. Blank cassettes come in a wide variety of configurations, replete with exotic ferric oxide formulations as well as chromium dioxide coatings.

Along with solid state electronics, these features have the cumulative effect of making cassette recorders available that have a 30 Hz to 15 kHz frequency response along with signal-to-noise ratios on the order of 58/60 dB. The owners of these cassette recorders have a voracious appetite for blank cassettes, whose sales keep skyrocketing higher every year.

As for commercially recorded music cassettes, there are thousands from which to choose covering every aspect of music. For quite a period it was a common practice of the record companies to have simultaneous releases of the same productions on disc and on cassette. The cassette world looked rosy indeed and, as you might expect, some of the rabidly enthusiastic cassette boosters and any number of pundits were claiming that the high fidelity quality of the cassette was as good as the phonograph record, and maybe even as good as open reel tape. Once again we were assured, the demise of the disc was at hand. However, in the midst of all this euphoria, you will note that I made my comment on the simultaneous disc/cassette release policy of the record companies in the past tense. And there, friends, hangs a tale ...

In this cold winter of our energy crisis discontent, the situation anent the release of recorded cassettes can only be described as bleak. The number of new cassette releases each month has been reduced to a trickle. RCA, for example, issues cassettes on a "selective" basis now, with only those productions they consider of "hit" status as candidates for the cassette format. Truth is, months have gone by without any RCA cassette releases. Ampex Stereo Tapes, once the fountainhead for a veritable torrent of recorded cassettes, is also operating on a "selective" basis. Of course, they represent so many different record companies, that even with this restriction, a fair amount of cassettes are released each month. Reduced output of cassettes is the order of the day with most record companies, with Columbia apparently the only record company maintaining its output at or near the levels of the past several years. To put this whole business of recorded cassette releases in the most candid perspective, let me say that it is fairly common knowledge within the industry that a number of companies would like to get out of the cassette business altogether.

The decline of the recorded music cassette is due to a number of factors. From the record companies viewpoint, it is simply a question of ever diminishing sales. Why are cassette sales down? To put it succinctly, and rather bluntly I'm afraid, the cassette at its present technological level cannot compete with the sound quality of the phonograph record. A strong statement this, and I can see the hackles rising on the necks of the cassette contingent. But examined dispassionately, in a direct cassette/disc comparison, the ear validates the quality differentials which tips the balance in favor of the disc. Before going into some of the problems encountered with recorded cassettes, let me state that I am not "anti-cassette," nor do I have any particular axe to grind for the phonograph disc. As far as I am concerned, the size, shape, speed or any other parameter of a music storage medium is entirely irrelevant. My one criterion is that the medium be capable of reproducing music with the highest possible fidelity.

I have been in Ray Dolby's laboratory in London where I watched him making Dolby B cassette copies from Dolby A-Type 15 ips master tapes. The cassette recorders he used were high quality units, but nonetheless were standard models available in any hi-fi shop. On direct A/B comparison between master tape and copy, it was difficult, if not impossible-to detect any difference between them. I have done the same thing with my equipment at home. The important factor here is that Dr. Dolby and I were making copies at a one-to-one ratio. This essentially is what every cassette recorder user does when he engages in the common practice of recording "off-the-air," or copies phonograph records. With virtually any standard recorder, using correct level settings, it is quite easy to produce high quality recordings, which is why this form of activity is so popular, and why sales of blank cassettes keep rising.

Contrast this one-to-one recording, with the standard duplicating process used in producing recorded music cassettes. Naturally the dictates of economy call for higher speed multiples in commercial duplicating, with a ratio of 32 to 1 in general use. There are problems enough with this duping ratio, so one is aghast when stories circulate about the use of ratios as high as 128 to 1! The tiny width of the cassette tape operating at these speeds imposes severe guidance problems in the transport of the slave recorder and often gives rise to tape "skew," which can cause crosstalk. In fairness, it must be said that nowadays the guidance problems are far fewer than they were several years ago.

The main problem with high speed cassette duplication is modulation noise. Modulation effects are caused by magnetic discontinuities. If the tape stock used for duplication has poor crystal structure, which cause the formation of dendrites (clumping particles and accretions which appear on the surface of the tape as protuberances), dropouts will occur. Although some of these dropouts would be detectable at the 17/8 ips real-time speed of the consumer cassette recorder, at the 32 to 1 duping speed multiple dropouts are passing by the recording head. This causes the sound on the recorded cassette to have an undulating, wavering sort of characteristic. On many types of music this is not too noticeable; the ear simply is aware of a general lack of clarity in the sound. However, in any music where woodwinds such as flute, clarinet or oboe are in an exposed position, especially in solo passages, the instruments sound blurred and buzzy.

When a consumer plays back a recorded music cassette on a unit which is in optimum operating condition, he may encounter any or all of the following. The sound may wow and waver in a rather gross fashion, especially noticeable during sustained piano chords. This wow is not inherent in the unit, but can be the result of a poor wind in the cassette tape pack or a poor quality and insufficiently lubricated inner liner in the plastic cassette. On sections of the cassette, the sound may exhibit occasional distortion because in the process of duplication the tape overload limits have been exceeded and the magnetic particles have become saturated. As mentioned earlier, the most frequent flaw is the "burbling" sound of modulation noise. I should mention that for the most part there are no problems with the playback of Dolby B Type cassettes, but there is the factor that because the Dolby process has reduced the tape hiss, this often makes the modulation noise more apparent.

It is all these noise and distortion problems, singly, or in combination, which have frustrated those people who have wanted to use recorded cassettes as a viable alternative to phonograph records. Of course, not all cassettes have these playback problems. Nor does everyone have the quality of associated playback equipment which is more revealing of these sonic flaws. Nonetheless, enough hi-fi enthusiasts are aware of the problems to account for the declining sales of recorded music cassettes.

Can anything be done to resolve these cassette problems? I should note here that the worst culprit, the modulation noise, is not a consequence of high speed duplicating ratios alone, but a combination of the speed and the quality of the tape oxide. As noted in these pages before, Advent Corp. is planning to issue recorded music cassettes which have been duplicated at a speed ratio of only 4 to 1 and use chromium dioxide tape. This approach is all right for a specialized "premium" product, but most engineers feel that this is not an economical idea for large scale duplication. Mr. M.B. Martin, an engineer for the Memorex Corp. writing in the November 1973 issue of the Journal of the Audio Engineering Society on cassette duplication, has some very interesting ideas. In essence, he feels that the modulation noise problem could be solved by the use of higher quality tape oxides, and he lists the various oxides and describes their properties.

He acknowledges the generally superior characteristics of chromium dioxide, such as the almost perfect acicular particle which makes it free of dendrites, its higher coercivity, improved short wavelength (high frequency) performance. He also points out that chromium dioxide requires a much higher bias current for optimum recording, it is higher in cost than any other oxide, and there are special equalization criteria to be met. Understandably, Mr. Martin is keen on Memorex's new MRX-2 ferric oxide tape, and gives some very cogent reasons for its use in duplication. If what Mr. Martin says holds up in practice ... and I'm inclined to think that it will ... it would be a shame if the duplicators didn't try such a product. As Mr. Martin points out, the extra cost involved in using his oxide is on the order of 3 cents for a C-60 cassette, and a nickel for a C-90 cassette. If the better oxides, used at the same standard duping ratios, results in a cleaner, better-sounding cassette free of modulation noise, the record companies should make such a product available to the consumer, even if it had to be sold at a slight premium to offset higher costs.

I have an experimental Dolbyized chromium dioxide cassette recording of La Traviata, sent to me by Ampex Stereo Tapes, and some similar cassettes from BASF. Significantly, they are free of modulation noise, although they are not perfect in all sonic respects, i.e. some tape saturation. It is food for thought at least, and maybe some people will be interested in the resuscitation of the recorded music cassette.

(Audio magazine, Mar. 1974; Bert Whyte)

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