By MIKE JONES
There was a time, not long ago, when the cassettes you recorded at home by copying LPs would sound superior to any of the music cassettes you could buy from your local record store.
The same cannot be said today. The current music cassette, duplicated at high speed using Dolby HX Pro (see Audio, August 1984) and the latest tape formulation, is capable of superb fidelity. Its quality can compare favorably to mass-produced vinyl records-particularly those with more than 22 minutes recorded on each side.
Dolby HX Professional and new tapes are just part of the story, for in truth the music cassette has under gone major development during the last few years, benefiting from better cassette housings, improved mastering techniques, and new duplicating equipment. Another important factor has been the attitude of the duplicators themselves: They are newly and increasingly determined that their cassettes will be the best they can produce, comparable to those that can be produced at home. Indeed, the leading duplicators are so committed to improving quality that many of them attended a seminar organized by Electro Sound in California last year, following a similar event in London, to discuss various ways in which the quality of music cassettes could be improved even further.
Strange as it may seem, the largest obstacle to progress on quality is not a technical problem for duplicators but one of persuading the record companies to make full use of current technology-let alone what might be developed in the future. Despite the large profit margins involved, some record companies are willing to use only the cheapest materials for cassettes, in order to achieve maximum profits. They say that the consumers who buy their products do not care about quality, and the evidence given to support this claim is that they receive very few complaints.
Boldly speaking, they have a captive market of 10- to 25-year-old music listeners who, if they wish to buy cassettes of their favorite groups, have to accept whatever quality the record company decides to pro duce. Why some record companies do not aim to give good value is quite beyond most analysts, especially since they could obtain enormous improvements in quality using their existing equipment by paying more attention to detail during the transfer and manufacturing stages.
I believe that it is incumbent on the record producer to insist on good quality throughout; indeed, he can help make the necessary funds available by not allowing his group to waste valuable studio time, as is often the case.
Quality from the Beginning
Even when the best materials are used, the sound quality of a cassette can be easily ruined by an inferior master, and many of the speakers and dele gates who attended the California seminar expressed concern over this. Ideally, the source master from which cassettes are duplicated should be either a digital or a first-generation analog copy of the stereo master. If subsequent-generation analog copies are used, the signal-to-noise ratio and distortion will deteriorate, thus restricting the dynamic range. Unfortunately, many record companies do not seem to realize or care about this, often sending fourth- or fifth-generation tapes for duplication. Under these conditions, it is this running master-not the cassette tape or the duplication process-that will limit the sound quality. A far better alternative would be to use digital transfer, which avoids many of these problems.
Before I go any further, I should explain why digital transfer is superior to analog with respect to deterioration of the audio signal. Once a recording has been converted to digital format, and providing that any subsequent editing, mixing or transfer is executed in the digital domain, avoiding D/A and A/D converters, it will not matter how many copies you make from the initial digital recording, or how many generations you produce-they will all sound identical to each other and will undergo no loss of quality.
The use of chrome tape and the ad vent of Dolby HX Professional have in creased the dynamic range of cassettes, so that the use of high-quality masters is more crucial than ever. This subject was considered so important by the seminar organizers that an en tire session was devoted to it. Ken Gundry of Dolby Laboratories gave an extremely interesting presentation on how Dolby HX Pro can be used to extend the dynamic range of music cassettes at high frequency, up to 10 dB at 15 kHz. When you listen to a cassette recorded with HX Pro, the improvement can be quite dramatic, with ferric tape sounding like chrome and the latter like metal. Some material similar to what Ken presented is shown here. In addition to demonstrating the beneficial effects of HX Pro on cassette tape, he also showed how easy it is for the performance of the running master to restrict the quality of the cassette, especially when the cassettes are duplicated at up to 64 times normal speed. Ideally, what we need is a method of extending the dynamic range of the running master as well as that of the cassette; this is exactly what is achieved by fitting Dolby HX Pro to the recorder on which the running master is recorded.
Two manufacturers, Otari and Studer, currently produce the new type of mastering machines. Studer has also improved the phase response and tape guidance of their recorder to in crease the stability of the tape as it passes across the heads. The result is a cleanup of the phase response at the top end of the spectrum and an improved stereo image. This has proved necessary because the masters for duplicating cassettes at 64:1 are normally recorded at 3 3/4 ips.
---------Block diagram of cassette duplication.
---------S/N in three frequency ranges, for master tapes and duplicated cassettes.
From left to right, the first two sets of bars represent 1-inch, 4-track tape
with Dolby B NR. The remaining four sets of bars are for cassettes duplicated
at 32:1 speed ratios, using Dolby B NR. Frequency ranges are: Low, 1 kHz for
open reel, 375 Hz for cassette; medium, 1 to 10 kHz; high, 15 to 20 kHz.
Upgrading or replacing existing equipment, to enable a duplicator to take advantage of Dolby HX Pro, is an expensive business. While there is no doubt in my mind that it is worthwhile, some duplicators say that they cannot tell the difference between cassettes which have been recorded with HX and those which have not. If this is the case, then they should look very closely at their system or their duplicating methods and masters, for something is definitely wrong.
Any doubters should try listening to the prerecorded cassettes, currently being produced by Capitol and EMI Records, which carry the "XDR" logo.
Not only were Capitol and EMI the first companies to use Dolby HX Pro on both sides of the Atlantic, they were also the first to develop a system whereby they could control the consistency and quality of the cassettes they produce on an international basis. The XDR program is one of continual development and one that benefits the consumer a great deal. Unlike the "Chrome for Quality" logo, the XDR symbol means that the cassette has been produced to exacting standards which cover the entire recording chain from studio to final product. If just one part of the chain falls below specification, then the XDR logo is not used.
I hope that Dolby Laboratories will control the use of the HX Pro logo in a similar way so it, too, will become a symbol of quality. There is no doubt in my mind that BASF missed a golden opportunity to improve the standard of prerecorded cassettes when they al lowed the industry to use the "Chrome for Quality" logo without any effective control as to how or when it was used.
Now all it really states is that chrome tape has been used, which doesn't say anything about the quality of the re cording-unlike XDR or Teldec's Direct Metal Mastering (DMM) logo, both of which do.
The Basic Particle
Having decided to produce the highest quality cassettes possible, what tapes are available to the cassette duplicator? The most common type is coated with gamma iron oxide, more commonly known as ferric, and it is similar to many of the Type I blank cassettes that you can buy. While gamma oxide tape has been around since the late '50s, the tape we use today is nothing like the product that was produced at that time. As Frank Diaz of Columbia Magnetics explained at the seminar, a new ferric particle is developed every five years or so. Modern ferric tapes are quieter, offer more dynamic range, and are far more stable than their predecessors.
But is ferric good enough, or is there something better? Judging the issue on purely technical grounds, I have to say there is a better product, chrome tape, and I believe that the majority of the experts who attended the seminar would agree with me. Chrome tape's superiority is largely due to the efficiency and shape of the chromium dioxide particle and the way in which it outperforms pure ferric formulations for most applications, including audio, video and data. Indeed, chromium dioxide could be regarded as the Rolls-Royce of magnetic particles.
In audio recording, chrome's output level is similar to ferric's at low frequencies, but it provides a higher output at short wavelengths, which enables it to handle synthesized music and digital recordings with minimum compression. Because the chromium dioxide's particle size is smaller and more uniform than its ferric counterpart's, chrome can be packed onto the tape more evenly and with greater density, thus reducing bias noise and tape hiss and increasing output. Of particular interest to the critical listener is the substantial reduction in modulation noise that is obtained with chrome; this feature, in my view, makes its universal use for music cassettes well worth while. In addition, an old problem has been overcome by the introduction of new manufacturing methods; print-through has been reduced to a point where the figures obtained for chrome are now lower than those for many cobalt-doped tapes.
------------- High-speed cassette duplication frequently uses a continuous-loop
master tape running at high speed through a loop bin. In this Electro Sound
8000 system, the master runs at 240 ips, while slave units record onto large
pancakes of cassette tape at 240, 120 or 60 ips. Quality increases as the slave
speed and speed ratio to the final cassette go down.
So, in pure audio terms, chrome has a lot going for it, and those recordings duplicated on chrome have a clarity and transparency that would be hard to obtain from any ferric tape. But be cause of commercial interests, chrome has not received the universal support from the industry that it should have obtained on purely technical grounds.
Like Dolby HX Pro, some duplicators cannot hear any improvement when they use chrome, but again, this is likely due to problems with their equipment or low-quality masters. What they must realize is that to achieve the excellent results that chrome is capable of, the duplicator must pay a great deal of attention to detail if there's to be an audible difference in the finished product.
Because of the impact chrome has had on the industry, other tape manufacturers who do not have licenses from DuPont to produce chrome have produced alternatives such as Magnetite (from Agfa) or CS-1 (from Capitol).
The initial results obtained with these new products are very promising, and in subjective listening tests they come close to those obtained with chrome. The important thing to remember is that all of them are a vast improvement over standard ferric formulations, providing they have been duplicated correctly and from a good-quality master.
Cassette Housings
Another seminar session dealt with cassette housings, and the majority of those attending agreed that, while the tracking accuracy of cassette housings has improved a great deal in recent years, there is still room for improvement. In truth, higher quality recordings place a greater demand than ever on the cassette housing (or shell), which has to be made more precisely so it can guide the tape across the playback head more accurately. Poor tracking will have the same effect as a playback head which is in need of azimuth adjustment.
Concern was expressed at the seminar over the way some consumers store their cassettes, particularly those who use cassettes in cars, where temperatures can easily climb above the softening point of plastic. The point to remember is that the plastic body of the cassette will distort long before it melts. Distorted housings will not track well, nor will they sound right.
I had the pleasure of moderating the final session of the seminar, where the attendees took a look into the crystal ball at the future of the industry. Of course, the conversation soon came 'round to the Compact Disc and alter native digital systems, such as the dig ital cassette. Most agreed that the Compact Disc will soon become the major competitor to cassettes, especially for the classical market, and that vinyl would eventually fade away. Although digital cassette systems are being developed in Japan, manufacturers have not yet agreed on a single common standard. Because of the public's general awareness of the Compact Disc and of improved re cording technology, a great deal of pressure will be put on the duplicating industry to improve the quality of cassettes even further. Pressure will also be put on the record industry to make use of current technology and future improvements. The danger is that the record companies may, in actual practice, do the opposite: Master from low-quality or noisy masters, as happened with the early Compact Disc releases.
As technology pushes forward we should take advantage of it in order to enrich our enjoyment of music. Under the leadership of companies such as Electro Sound, the duplicating industry has demonstrated that the quality of prerecorded cassettes can be very high indeed. However, it will only be through increased and continued public pressure for quality recordings that the market will more widely exhibit such quality. So long as sales and profits do not suffer because of low quality, record companies can hardly be blamed if they let quality slide by not investing in newer and better equipment and materials. They are, after all, in business to make money, and they need to be shown that Gresham's Law (that bad money drives out good) does not apply to music cassettes.
--------- Tape-tracking errors due to cassette-shell defects, such as the
slanted pins shown in the lower drawing, have the same effects as playback-head
azimuth alignment errors.
Table I--Tape speeds in various duplicating systems.
(Audio magazine, Jun. 1985)
Also see:
Cassette Test Update: 12 Formulations (Sept. 1984)
58 Cassettes Tested (Sept. 1978)
Performance of High Energy in Magnetic Materials in Audio Cassette Recording Tapes (Sept. 1978)
Cassette Tape Update: 49 Formulations (Jun. 1986)
= = = =