by HOWARD ROBERSON
At least once a year, Audio tests a number of the latest cassette tape formulations. The effort is concentrated on electrical performance, such things as frequency responses and maximum record levels. It has been a regular practice to check flutter and skew effects, but we have not taken a detailed look at the mechanical inter-relationships that are involved. This article delves into such questions as: Is there such a thing as a low-flutter cassette? Does it make a difference which deck is used? Do all tapes skew? What should I look for in a cassette if I want good mechanical performance? Are some cassettes more reliable than others?
Fig. 1--TDK's new Metal Alloy audio cassette comes housed in a Reference
Standard mechanism/shell. (Photo, courtesy TDK.)
Fig. 2--Disassembled Reference Standard mechanism. (Photo, courtesy TDK.)
Even with just a cursory examination in the course of buying tapes, you may have noticed that there is a great deal of difference in the way that the various manufacturers package the product.
This can be more important than it might at first seem. To minimize the possibility of getting harmful dust on the tape itself, the package should be sealed in some sort of plastic wrap. The little tab seal used by a few manufacturers will assure you perhaps that the tape has not been used by someone else, but the openings in the typical cassette box can allow a lot of dust to enter. After opening the pack age (a pull tab is a worthwhile convenience), follow good practice in keeping the cassette in the box when not actually being played. Do not store any tapes in dusty environments. If you must do so, try some of your own plastic protection, or stick to cassettes with better quality boxes with tighter closures. The new Memorex boxes provide better sealing from dust than the older standard-design ones do.
If you have purchased a number of different tape formulations, you will have learned that manufacturers do not agree on what makes the best label. We're not going to dig deeply into this question, but there are a few things to keep in mind. First of all, is there enough space to write in the necessary identification? Some labels are so small, you might need to use some sort of code or abbreviations. What can you write on the label with? Best of all are those which will accept almost anything, but some require a ball-point pen, making changes very difficult. Some cassettes have extra press-on labels, which is a definite help. Take a look at the outside card while you're at it: Some are good, and some have failings similar to those discussed for labels.
Now that we've talked about the wrappings and labels, it's time to take a closer look at the cassette shell itself.
Figure 1 shows the assembled TDK MA-R cassette, the most sophisticated design currently available. It is also relatively expensive, of course, so it is not surprising that most other assemblies are less impressive. The great majority of the premium cassettes sold have plastic half shells which are held together with screws. There are just a few that are sonic welded together, and their manufacturers feel that sonic welding can do just as good a job as screws. It is true that screws must be torqued correctly to hold firmly, but not so tight as to introduce unwanted stresses. It is also true that most of the really cheap cassettes are sonic welded, and that the cassette shells which are most nicely finished are all held together with screws. It is possible, of course, for a manufacturer to use more than one quality of shell and mechanism in its product line. TDK actually uses four, the Reference Standard Mechanism for MA-R tapes, the Laboratory Standard Mechanism for MA and SA-X tapes, the Super Precision Mechanism for SA, OD and AD tapes, and the Precision Mechanism for D tapes. We can't say that this is just the way to do it, but there is a great deal of sense in using a higher quality mechanical assembly to go with higher quality formulations.
To aid in the discussion of design requirements for the assembly, let's examine Fig. 2 which shows a disassembled Reference Standard Mechanism. In the center is the die-cast metal frame which must, and does, provide rigidity and stability, accurate outside dimensions and good finish, good support and accurate location for other components to be mounted in the frame, and parallel sides for mounting the cover plates. The cover plates must be flat with some rigidity and accurately dimensioned. The assembly of these two components has to provide the basic inside space for tape storage and guidance. There are two static-free slip sheets for low-friction restraint of tape wander during play or wind. Now, a cassette shell that is made out of plastic should meet the same basic criteria, ac curate dimensions, rigidity, stability, etc.
Carefully examine the cassettes you are using for surface smoothness, traces of plastic flash, resistance to bending or twisting, etc. Don't try to find their stress limit, but you may be able to weed out some questionable tapes.
When the tape pack is set into the shell, it is threaded over guide pins at each end and then over guide rollers, passing in front of additional guide pins, the tape pressure pad, and the mu-metal magnetic shield. For good mechanical performance, there are criteria that the tape pack itself must meet. The width must be constant, the slitting must not cause any deformation of the edges, the cutting must be a perfectly straight line, with no skew introduced, and the leader must meet the same criteria. As a fast check of the cassettes you have, look at the surface of the tape at the edge of the cassette. It should be perfectly flat and smooth. Any cupping or rippling might cause a range of tape problems, drop outs, changing levels, high flutter, and its getting wrapped around the capstan.
It comes down to this: To get the most out of the tape, it must remain in intimate contact with the heads--easy if its own surface is flat (except as shaped to the head), impossible if its own surface looks like a badly misaligned tire.
Fig. 3--How tape skewing causes alignment errors. A, basic mechanical
interface. B, record head adjusted for same angle with tape as play head.
Note skewing tape. C, results from turning cassette over without readjusting
the record head. The effects are greatly exaggerated for clarity.
The tape must be fastened to the hubs, and yet the hubs must not intro duce any bumps as the tape winds on. The hubs must also be accurately round and concentric with the hub-drive opening. All the stationary guide posts must be perpendicular to the shell-frame reference plane. Their surfaces must be long-wearing and must not damage the tape in any fashion. The guide-roller surfaces must be smooth (TDK states "seam less"), concentric with the bearing pin (stainless steel preferred) and with flanges that guide and control tape wander without causing any edge damage. The magnetic shield should be accurately positioned behind the pressure pad. There are different approaches to the design of the pad and its support. Do check to see that the pad surface is flat to the tape and not misplaced crosswise. It is impossible to check out the internal construction of a typical plastic-shell cassette, unless you take it apart. Per haps if all that is not worthwhile, you would want to check what the manufacturer claims he has done to make his cassette a good one mechanically. If the edge of the cassette mates poorly and is not straight and smooth across, you should be suspicious of any claims for internal excellence. The key words are smooth, flat, perpendicular, parallel, round, concentric, rigid, stable and accurate.
With a few artistic liberties, Fig. 3 shows some of the cassette/recorder alignment relationships and how tape skew affects head alignment. In "A" the guide pins and rollers are shown to be exactly perpendicular to a rigid shell. The molded-in guide pins near the center of the cassette must also meet this criterion. The drive capstans and the record and play heads are shown as perfectly perpendicular to the recorder sup port assembly, which supports and positions the cassette shell exactly. This is our ideal of course, and if the tape ran perfectly straight, maybe it could really happen. First of all, recognize that if the cassette is not positioned accurately relative to the recorder components, some of the accuracy in the cassette itself is defeated. In other words, when you insert a cassette, make certain that it seats firmly into position. If there seems to be a favored position for best performance, use that all of the time.
Fig. 4--Record/ playback flutter with Akai GX-F90 deck. Top, TDK MA-R cassette;
bottom, BASF Studio I cassette. (Scales: Vert., 0.05 %/div.; hor., 1 S/
div.)
Fig. 5--Record/playback flutter with Technics RS-9900/US deck. Top. TDK MA-R cassette; bottom, ferric cassette. (Scales: Vert., 0.05%/div.; hor., 1 S/ div.)
Fig. 6--Flutter spectrum with Akai GX F90 deck and TDK MA-R cassette. Scales: Analyzer bandwidth, 1Hz; 'scope. vert. 10 Hz/div.. hor.. 10 dB/div.)
Now let's take a look at how tape skewing affects head alignment and record/playback performance. In "B" of Fig. 3, the play head is shown to be perpendicular to the support plate with the tape curving across it. The curvature of the tape and the resultant angles are greatly exaggerated to facilitate demonstrating what happens. The lines on the tape, are radial lines of the curve and perpendicular to the edges. If we adjust the record head to get it in best alignment with the play head, we get the result shown in "B." Next we flip over this cassette ("C") to see how things would work out, without readjusting the record head. For the play head, the radial lines are just put at the same angle on the other side of vertical. With the record head, however, the angular error is twice what it was before any adjustment.
These simple figures tell us a number of things about what is desirable and what to expect. Most desirable are cassettes which have no skew and which will seat accurately in the recorder. With such tapes, alignment with both heads will remain correct, including when the cassette is turned over. Maybe this sounds unlikely, but, in fact, we have been able to report on a number of tapes that consistently do not have detrimental skewing from sample to sample and from side to side, including both C-60s and C-90s. Obviously, the problem of poor responses from skewing is more severe with separated record and play back heads. Note, however, that skewing can cause some loss in response even in combination record/playback heads. This is particularly true if you are going to play a tape on another deck than the one used for recording.
We know that smooth tape motion is essential for low flutter and that rough mechanical motion would result in high flutter, but how much does it have to do with the deck? The first part of the investigation utilized an Akai GX-F90 which had shown low flutter, the Nakamichi 582 which had average flutter, and the older-design Technics RS-9900/US.
Figure 4 has plots of the record/play back flutter with the Akai deck using a TDK MA-R (top) and a medium-price ferric (bottom). The straight lines are the reference zeros, the vertical scale is 0.05% wtd. pk. per division, and in creasing flutter is in the negative direction. The 'scope traces show a number of peaks not indicated on the meter, but there is no doubt about the much lower flutter with the MA-R (0.03% meter) compared to the ferric (0.08% meter).
When we tried the same cassettes in the Technics RS-9900/US (Fig. 5), the flutter with the MA-R was higher, the flutter with the ferric was lower, and they were pretty much the same with this deck.
Fig. 7--Flutter spectrum with Akai GX F90 deck and a ferric cassette different
from the one used to generate the bottom curve in Fig. 5. (Scales: As in
Fig. 6.)
Fig. 8--Flutter vs. tape and deck. Top. mediocre cassette with Nakamichi 582; 2nd, poor cassette with 582; 3rd, mediocre cassette with Aiwa AD-3600; 4th, poor cassette with AD-3600, and bottom, poor cassette with Aiwa AD-M700. (Scales: vert., 0.1% wtd. pk./ div., hor 1 S/div.)
Fig. 9--Record/playback 10-kHz phase error and jitter between channels. (Scale: Hor., 30 deg. /city.)
Fig. 10--The two Loran cassettes shown here were exposed to high temperatures
in environmental test chambers along with four leading cassette tapes,
labels removed. (Photo, courtesy Loranger.)
We went back to the Akai deck and plotted (Fig. 6) the MA-R flutter spectrum for 50 Hz each side of our test tone with a 1-Hz analyzer bandwidth. There are sidebands at ±4 Hz, 23 dB down, and at ±24 Hz, 35 dB down. Figure 7 shows the results with the same deck and another ferric cassette, which had shown twice as much flutter on the meter as the MA-R. Note that the side-bands at ±25 Hz are up to-21 dB, and that there is a lot of energy at a higher level at other points. Similar checks with the Nakamichi 582 showed spectra with reduced discrete sideband levels but with considerable "random" energy close to the test-tone carrier. The meter reading of 0.09% wtd. pk. was indicative of the total level of these many flutter components, even though the energy was not concentrated in a couple discrete frequencies.
Subsequent to taking the above data, two Aiwa decks were obtained which had low flutter with many cassettes. A search was made to find cassettes that had mediocre to poor flutter performance. The results from some of these tests are shown in Fig. 8. Please cote that the vertical scale is 0.1% per division, as compared to 0.05% per division in the earlier figures. As before, the straight-line traces are the reference zeros, and increasing flutter is downward.
The two topmost sets were run with the Nakamichi 582. The so-called mediocre cassette showed no values greater than 0.08% wtd. pk., and an excellent 0.05% was typical. The poor cassette was really that with relatively frequent readings to almost 0.2%, and a few close to 0.3%! The next two sets were made with the recently introduced Aiwa AD-3600. Preliminary tests had shown very low flutter with many cassettes. The first run with the "mediocre" sample showed most readings below 0.06%, with around 0.04% or less very common. These are certainly excellent figures, but on to the challenge of the cassette that had per formed so poorly just before in the other deck. These results (next to the bottom of Fig. 8) were quite unexpected, but the plotted figures were really quite typical--few peaks over 0.06%, with most meter indications less than 0.04% wtd. pk.! This low-flutter result left space for a run with the same cassette in the Aiwa AD-M700 deck, which had also shown well-controlled flutter. There is a notice able increase, compared to the AD-3600 deck, but the 0.08% maximums are still quite acceptable and much lower than the Nakamichi 582 results. In case there is any question, let it be stated here that exactly the same section of tape was used for each recorder and re checks were made of all the results.
In general, if you need very low flutter, you must have a good performing deck as well as a good cassette. A cassette cannot force a deck to have low flutter, but many decks are definitely sensitive to the characteristics of the cassette.
The Aiwa decks used in the tests reported above were the best seen to date in giving low flutter, regardless of the cassette used. Under a number of conditions TDK MA-R appeared to be the lowest flutter cassette. Some of the other good-performing tapes were Ampex EDR, GMI and GMII. BASF Professional II and III, Fuji FX-I. Maxell UD-XL I-S and UD-XL II-S, Memorex MRX-1, Osawa Cr, Realistic Supertape Chrome, Sony SHF, and TDK MA and SA-X. These conclusions must be considered tentative be cause of the limited, relatively short-time testing and because of the proven influence of the deck.
The last of the tape/recorder inter face effects to be discussed is record/ playback phase jitter. If the tape motion were perfect across the head, without waving or vibrating, there would be no shifting in time between channel A compared to channel B. Figure 9 shows the output of both channels of a recorder with a 10-kHz test tone, and with the scope locked to "A" (top). The relative phase jitter of "B" causes the trace to move back and forth on the screen, as shown in this timed exposure. The sweep speed was adjusted for 30 degrees per division, and we can see that the total jitter is about 40 degrees, which is fairly good for a cassette deck. A misalignment of about 40 degrees was purposely left in, evidenced by the displacement of the average position of the "B" trace. This angular discrepancy of the 10-kHz tone indicates an 11-uS time difference. Actual jitter and alignment errors can be much greater than that shown. The conclusion drawn after a series of tests with a selection of cassettes and a number of decks was this: Phase jitter is primarily determined by the deck, but the cassette has some influence on the exact results. The deck with the smallest distance between the record and playback gaps is most likely to have the least jitter. Recognize that such jitter will exist in any subsequent playback. It is also a fact that jitter and skewing can cause fairly high level losses at the higher frequencies when a tape is played back on another recorder, especially when there are head alignment errors.
At the time of this writing, Loranger has just introduced a line of cassettes which have shells made out of Lexan.
Among other things, the manufacturer claims that these shells are much more stable with elevated temperatures, such as might be found in car tape players.
Figure 10 does show very noticeable damage to the non-Lexan shells, so I subjected C-60 spares to oven temperatures of 120° to 160° for one hour, a temperature period that might well be found on a car dash. I found that the cassettes most sensitive to heat distort quickly. Only one-third to the end, though some shells were a bit distorted. The Loran Lexan shell showed the least effect, and it should be noted that the Maxell shells showed very little warp. This certainly is a valid area for investigation, and I will try to gather more information for possible publication later or.
Winding
In past years, there were a fair percentage of cassettes that would not survive very many fast winds, and occasion al ones that would not even play through one time without jamming. These types of failures are now much less frequent, and there are fewer cases of various types of sounds, squeaking, moaning, chattering, etc. There are still tapes, however, that are very noisy on one deck and most quiet on another. In general, it appeared that the cassettes with the smoothest winds (quietest) had the lower flutter and the least likelihood of jamming. There were a number of exceptions, and only very lengthy testing would prove whether there is much of a correlation. Good guidance to the tape pack with slip sheets did reduce over the-pack failures. Finally--and once again--the total cassette system performance depends upon the mechanical and electrical characteristics of both the tape and the deck.
The New Cassettes: Performance Update
by HOWARD ROBERSON
Fig. 1--High-frequency losses with repeated plays vs. tape type and deck used Top. Maxell UD-XL I-S on Nakamichi 582, second, Maxell UD-XL on 582: third. Maxell UD-XL I-S on Aiwa AD-3600. bottom: Maxell UD-XL II-S on AD-3600
This annual cassette tape survey covers 29 different formulations, 14 Type I (ferric/normal), nine II (chrome-type/high bias), two III (ferrichrome type), and four Type (metal particle). There are both new and updated versions of well-established products. Of particular interest tapes from manufacturers new to industry, such as Loran (from Loranger Manufacturing) and Osawa.
The Audiophile's Choice and Direct-to Recording have products with the material itself made by others. Each the manufacturers was requested to supply three each of both C-90 and C-60 lengths. Three samples allows the consistency of the product and the second length gives an indication of possible performance shifts with a in length by the user. Some of manufacturers did not supply all the requested for one reason or an but tests were conducted on what was supplied. Table I lists to what extent supplied the manufacturer's and prices.
We had pretty well standardized our scheme from past years' expert but some recent events caused us add some checks not run before. For one thing, it had been rather difficult to get consistent flutter data, so tests were this year on a number of samples three different-model tape decks had been some question raised as the validity of making cassette tape on a particular deck which is not such as the Nakamichi 582 is the one used for such tests. A of crosschecks were made on and maximum record levels three other, "more-typical" decks assess some possible discrepancies. Although the other-deck testing was not all complete in comparison with the tests, there was confirmation of all in a relative sense for each of the investigated.
As in the past, responses were made a swept-sinusoid source from 20 Hz 20 kHz. To ensure that each of the shown was a true playback they were made by recording sweep, rewinding the tape, and then the response on playback. With three-head deck, it is very easy to such plots simultaneously while re Unfortunately, this method can spurious results since there may be inter-head leakage or effects from bias leakage, or perhaps insufficient allow ante for the time-delay effects among the record, playback, and plotter relationships. The UREI 200 plotting system used locks to the frequency of the play back signal it is not dependent on time synchronization.
TABLE I--MANUFACTURER'S SPECIFICATIONS
The swept responses were made at both Dolby level (200 nWb/m at 400 Hz) and 20 dB below that. In addition, an investigation was made of the possible losses at high frequency with repeated playings. I had planned to run some tests, primarily comparing CrO2 and Fe Co formulations, based upon comments made by various people feeling that the Cr02 tapes "kept their sound better. The interest in this particular facet was heightened considerably by letters to Audio from a reader, Edward F. McLain, Jr.
Mr. McLain had observed high-frequency losses with repeated playbacks with one of his recorders, and he had con- ducted a fairly extensive series of tests to pinpoint the cause. It seemed a bit surprising that he was having this problem with a Type I tape; immediately, such a thing seemed more likely with an out-of-date cobalt-doped formulation. Mr. McLain very nicely provided copies of his own plots, and there was no doubt about the losses with repeated replays.
A check among three decks on hand showed that there were similar losses with the Nakamichi 582 and the Aiwa AD-M700 decks, but no such losses with the Aiwa AD-3600. Figure 1 shows part of this comparison. Fifteen replays were made with each tape/recorder combination. Just the first, second, fifth, tenth. and fifteenth were plotted for UD XLI-S and the 582 deck. All other traces are the results of 15 consecutive overlaid plots. The repeatability with the AIWA AD-3600 with either tape is quite evident. The AD-M700 deck was used to get the data on all tapes under test as it could be set for automatic cycling of one playback after another. The output level of the 1 5-kHz playback was recorded on a strip chart for easy comparison among tapes and more accurate data reduction. There does appear to be some element here of pressure and/or tape tension, perhaps related to the magnetostriction and Curie-temperature proper ties of the formulation. We do not have a definite explanation for the reader on how this effect occurs. What we do re port later is the 15-kHz loss for 10 replays on a particular deck. You may never experience this problem, but you will know that it is a possibility, and that it appears to be most likely with a Type I tape. Perhaps the tape and deck manufacturers will solve the problem and educate us all at the same time.
The maximum record levels were those where a 3% DL (distortion limit) was reached with harmonic distortion checks form 100 Hz to 2 kHz and twin tone IM tests from 5 to 10 kHz. The signal-to-noise ratio was referenced to the 400-Hz DL, and IEC A weighting was used. Modulation noise checks used a 1-kHz tone at reference level, with the tone notched out and 500/1500 Hz bandpass filtering on playback. Data was taken on the sensitivity and bias of each tape, but the correlation to the manufacturers data sheets (were supplied) was not high. The bias figures obtained are reported as a guide--within a particular tape type--for possible high-frequency response shifts from changing a tape without readjusting bias. Remember that going to a higher bias tape will get boosted high frequencies. and going to a lower-bias tape will result in a loss of high frequencies, un less the original bias is changed to match the new tape. Skew was measured with pink noise and a 1/3-octave RTA and observing the effect on the high-frequency levels with turning the cassette over, after record-head alignment for the first side. A 3-kHz tone was used not only for the flutter checks, but for tests of output-level stability and dropouts.
TABLE II TEST RESULTS
Test Results
The great majority of the numerical data from the tests are listed in Table II. Take note of the fact that the tapes are listed alphabetically in type number categories. There are also frequency response plots for each formulation for both C-90 and C-60 lengths, if both were supplied. Also included on each of these figures is the 3% DL (distortion limit--harmonic or twin-tone IM) from the MRLs for the C-90 (for the C-60 only if no C-90 was supplied). These maximum record levels (in dB in Table II) are referenced to the 400-Hz record level for 200 nWb/m in playback. The actual output levels will be different to the ex tent there are response variations from flat and compression because of the high levels. Below there are additional comments on each general type and on each specific formulation.
Type I
-----------------TYPE I
The general impression of these tapes was that there had been a general improvement in the quality of what was available. This was particularly notice able in better output-level stability and lower skew. The losses at 15 kHz with repeated plays (on the test deck) were pretty much restricted to this type, al though there was quite a range of losses from one tape to the next. A number of cassettes had excellent performance in all respects.
Ampex ELN: The frequency responses of this new formulation were quite smooth and extended, and could have been made more so with a slight de crease in bias. It had average performance for the group (a good one) in other areas. There was slight skewing on some samples, and it varied with time.
The output-level stability was good, and the occasional dropouts just approached the audibility threshold. Flutter and the 15-kHz play loss were average, for all of the cassettes tested.
Ampex EDR: The performance of this formulation was very close to that of ELN, and slightly less bias would have extended the EDR's responses as well.
The MRLs were a little on the low side for current cassettes. Flutter was slightly less than average, but the 15-kHz play loss was above average. Output level stability was excellent, one of the best measured. There were no dropouts during the test period, and the maximum perturbation was only 0.5 dB.
AudioMagnetics Tracs: This tape was not quite average in performance for the group, but its low price could make it appealing for a number of uses. Flutter was average, and the 15-kHz play loss was less than average. There was very little skewing in any of the samples, including the C-60s. The output level stayed fairly constant (within 0.4 dB), and the few dropouts never approached the audibility threshold.
AudioMagnetics High Performance: The performance was good in most respects, with nice responses and good MRLs.
There was very slight skewing on some of the samples, not enough to be detrimental. Bias needs for the C-60s were slightly less than for the C-90s, generally true for most of the tapes tested, a minor effect at the highest frequencies. Flutter was just slightly above average, and the 15-kHz play loss was above average.
There was an occasional 0.3-dB wander in the 3-kHz output level, quite minor.
There were few dropouts of very small amplitude.
Audiophile's Choice: This brand is new to the test program, and the results indicate quite a good product for its fairly low mail-order price. The 15-kHz play loss was less than average (for Type I tapes), but flutter was higher than most.
The MRLs and S/N ratio were good, and the output-level stability was within 0.3 dB peak-to-peak. Infrequent drop outs were just to the audibility threshold.
BASF Performance: The responses were good with this formulation, but the MRLs were among the lowest for the Type Is, and noise was rather high. Skew was very small among all of the samples, including the C-60s. The output level remained steady; there were a fair number of dropouts, but they were of limited depth. Flutter was average. The 15-kHz play loss was less than average.
BASF Professional I: This is one of the better Type I cassettes with good responses and high MRLs. The output level stability was fairly smooth, although there were some dropouts approaching the audibility threshold. There was just a little skew with some of the C-90 samples, even less with the C-60s. Flutter was average. There was no 15-kHz re play loss, a possible advantage to owners of high-tension (?) decks.
Direct Agfa Super: In general, this relatively low-priced mail-order offering de livered above-average performance. Responses and MRLs were really quite good. On the other hand, there was noticeable skew at times, actually affecting the response plots. There was some wandering in the output level, but it usually kept within 0.5 dB overall. Dropouts were infrequent and of low amplitude.
The 15-kHz play loss was above aver age, but flutter was very slightly lower than most.
Fuji FL: The responses were quite good, but the MRLs were lower than the aver age for Type I. There was some skew with the C-90s, substantially none with the C-60s. Flutter and the 15-kHz play loss were both a bit less than average.
The output level was stable within 0.3 dB, and there were few dropouts, none of any significance.
Fuji FX-I: One of the better Type I tapes with excellent responses, good MRLs, and a high S/N ratio. Skew was very low on all samples. C-60 bias was very close to C-90 bias (most showed more difference). The output level was very stable and smooth, and there were no drop outs. Flutter and the 15-kHz play loss were both somewhat lower than aver age.
Loran Ferric/Normal: The products from Loranger Manufacturing are of interest not just because they are newcomers to the industry. Their cassettes are the most expensive in their respective type categories, which has to raise more than a few eyebrows. Everyone claims a quality product, of course, but Loranger literature is quite emphatic on this point.
Their most salient feature for many will be the r use of Lexan for the shell, with claims of greatly superior thermal stability. The tape itself showed good responses and MRLs, but the modulation noise was the highest of all tapes tested.
There was some skew, more so with the C-60s. There appeared to be a shifting of bias needs with time, but this might have been confused by skew problems The output level was stable, and all dropouts were less than half way to the audibility threshold. Flutter was about average. The 15-kHz play loss was less than average.
Maxell UDXLI-S: Once again, one of the UD series sets the standard for others to follow. Smooth, wide responses, very high MRLs, the lowest modulation noise of all tapes tested and next to the best S/N ratio. In addition, there was no skew observed in any of the total six samples. The output level stability was excellent, and there weren't really drop outs, just infrequent perturbations to-0.8 dB maximum. The flutter was less than average. On the other hand, the 15-kHz play loss was the greatest of all of the tapes tested, and it appeared that additional plays would have brought additional loss.
Memorex MRX-1: The tests were con ducted on C-60s only, as the manufacturer did not supply C-90s. The responses were wide, the MRLs were very high, and the S/N ratio was the highest for Type I tapes--in other words, one of the best of the tapes tested. There was very little skew in any of the samples. The output level stability was quite good. Although there were observable dropouts quite frequently, none of them reached the audibility threshold. Flutter was slightly less than average. The 15 kHz loss with repeated plays was much higher than most.
Realistic Supertape Gold: The test results of wide responses and high MRLs puts this Radio Shack product into the category of one of the better Type I tapes, with a price that is certain to in crease its appeal. There was less than average loss in the 1 5-kHz replay tests, but there was noticeable skew, which can result in high-frequency losses.
Flutter was average. There was some variation in the output level, but it was always less than 0.5 dB overall. There were many small-amplitude dropouts, but none observed of any significance.
Type II As the Type I tapes have continued to improve, there has become less and less difference between their overall performance and that of the Type II tapes. Of course, there are good and bad in each category, but there are some criteria we can consider in making any comparisons. First of all, an examination of the results table and the Type I and II response plots will reveal that from the standpoint of responses and MRLs, the Type Is are just as good, or even better than the Type IIs with the test deck used.
Note specifically that the Type II MRLs are lower than the Type l's until 10 kHz.
Some of the Type II S/N ratios are better, but Maxell UD-XL I-S and Memorex MRX-1 are better than many Type IIs, including their own corresponding products. (The 70-µS EQ, however, gets lower noise in the high-frequency region.) It is at least interesting to note that the fall off in the DL (or MRL) curve is similar in slope and level at 10 kHz for all Type I, II, and III tapes. Type IV tapes have similar DL-curve slopes, but the 10-kHz point is higher. We are not certain of the significance of the many possible contributing factors, such as equalization, properties of the pigments, head design, etc. We can see that if this curve is accepted by the tape user as a practical limit because of distortion, the Type IIs would offer limited advantage over the Type Is, which offer higher distortion limits at lower frequencies. The exception, of .course, is the lower tape noise with 70-µS EQ. It should be noted that a number of tests were run using other decks than the test Nakamichi 582, and the Type I and II MRL results were generally the same.
BASF and others have not joined the ferri-cobalt bandwagon and emphasize that they believe that CrO2 is the superior material. In the Type II plots that accompany this section, the tapes using CrO2, except BASF Professional II, can be characterized as having considerable loss in level with increasing frequency, particularly at Dolby level. There may be less total difference between highs and lows at-20 dB, but the final rise at the highest frequencies causes of a saddle like response. There did appear to be some rise in the low end with the 582 for all tapes, but it was less than a dB at 100 Hz most of the time. Tests were run with four other recorders, and the responses were almost exactly the same.
Perhaps there are decks which will deliver flat responses with these tapes, out none of the five decks tried would do so.
Good Dolby system performance requires flat responses, so there may be problems in the use of a tape with a response saddle (or mound).
AudioMagnetics High Performance II: Fairly good responses and moderate MRLs give the tape a fairly good Type II rating. There was very low skew among all of the samples. There was no 15-kHz play loss, but flutter was higher than most. The general output-level stability was good, but there were many drop outs up to the audibility threshold. The sample passed all of the functional tests.
BASF Professional II: This true chrome tape had among the highest MRLs, and the S/N ratio was the highest for the Type IIs. The responses were excellent in notable contrast to the other Cr02 tapes. Overall, this is one of the best Type II tapes. There was no skew among all of the samples, except for one short period during test. The output-level stability was excellent, and any of the drop-outs were very limited in amplitude.
There was no 15-kHz play loss. Flutter was below average.
Direct Type II: This mail-order tape corn pared most favorably with others, showing good responses and MRLs, low modulation noise and a high S/N ratio, as well. There was considerable skewing with both lengths, but there was very little 15-kHz play loss. Flutter was slightly above average. The output level was constant on the average, but there were some rapid fluctuations up to about a dB p-p. There were many dropouts, but only occasional ones approached the audibility threshold. There were no Type II sensing holes, which prevents use on some machines.
Fuji FX-11: The responses were good, and the modulation noise was low, but the MRLs and the S/N ratio were moderate.
There was very little skew or loss in 15-kHz playback. The output level was very steady, and there were only a few fluctuations of limited amplitude that might have been called dropouts. Flutter was average.
Loran High Bias/Chrome: This is the other Lexan-shell cassette introduced by Loranger, and it also includes the handy built-in, rotatable erase-prevention tabs--easily set for "safe" or "record." The manufacturer states that there is a double layer, ferric oxide for "low-end boost" and CrO2 for "high-end boost." As the plots show, the middle, unfortunately, gets left out, and there is a noticeable loss in highs at Dolby level. The S/N ratio is high, but so is the modulation noise. There was substantially no 15-kHz play loss, but there was a little effect on the highs by occasional skewing. Flutter was average. There were mi nor wanderings of the output level, probably undetectable. There were many dropouts, occasionally up to the detection threshold, very rarely over.
Maxell UD-XL 11-S: This is one of the best Type II tapes with wide, flat responses, high MRLs and S/N ratio and low modulation noise. There was no skew observed in any of the samples of both lengths, and the measured 15-kHz play loss was close to zero, 0.1 dB. There was a little roughness in the output, but the average level was stable. There were quite a few dropouts, although none approached the audibility threshold. The flutter was slightly better than average.
The cassette passed all of the functional tests.
Memorex HBII: This new formulation immediately showed itself to be one of the best of the type IIs, smooth and wide responses, high MRLs and S/N ratio, and very low modulation noise. Skewing was slight, and there was no 1 5-kHz play loss. Flutter was very slightly above aver age. The output had a 0.4 dB bump every three seconds, and the dropouts were fairly frequent although none were deep enough to be detectable. There were no Type II sensing holes.
Osawa Cr: The manufacturer states that the tape is a dual-layer cobalt-doped ferric. Cobalt-doped tapes in the past have not been that good, but this formulation performed quite well in all respects, including zero loss with 15-kHz playback.
There was Pose to zero skew among all of the samples. The output level was very stable, and there were substantially no dropouts. Flutter was average.
Realistic Supertape Chrome: For the most part, this tape would be classified as one of the better Type IIs. MRLs were quite good, and the S/N ratio was quite impressive. Skew, however, was erratic at times, and rapid variations in level in the 15-kHz play tests required some guessing at levels. Flutter was very slightly below average. The output level was stable on the average, but the fast analyzer scan to check for dropouts showed many rapid variations up to 2 dB. Fortunately, only rare ones got to the 3-dB detection threshold.
------------TYPE II
Type III
There are very few Type III cassettes being manufactured, and a number of decks do not have provisions to ruse them. In general, they have shown various performance limitations in the past, poor high-frequency headroom, a saddle-like response at lower levels, and poor amplitude stability. Lately BASF has been promoting their Professional III for car use, and they could work reason ably well for that.
------ TYPE III
BASF Professional Good MRLs at low frequencies, but more limited at high frequencies and high levels, causing a considerable slope in the response at Dolby level. The results shown were checked on other recorders, and they showed as much or more discrepancy between the 200-Hz and 2-kHz levels. The S/N ratio was high, but so was the modulation noise. There was very low skew, and there was relatively little 15-kHz play loss. Flutter was below average (better).
The output level was constant over a period of time, but there were many rapid variations revealed in a fast analyzer scan up to a dB, with occasional drop outs up to the detection threshold. Osawa FC: This is another dual-layer formulation from this manufacturer, and it showed less of the response deviations of the typical FeCr. There still was limited high-frequency headroom, however.
There was very little skew in any of the samples, and there was no 15-kHz play loss. Flutter was average. The output level showed some cycling, but it was limited to a total of only 0.3 dB. There were quite a few small-amplitude drop outs, none of them even close to the detection threshold.
Type IV
-------TYPE IV (Metal)
Each year other manufacturers join the metal tape suppliers, JVC, Memorex and Osawa this year. Because only one sample each was received for the two JVC and the one Memorex formulations, the results must be considered as tentative. It is impossible, of course, in these cases to make any statements concerning consistency. Along with other types, metal tapes have been get ting better in the areas of amplitude stability, skew, and dropouts. Some readers had written about certain problems in including loss of pigment on guides, rollers, etc. Perhaps there was some sort of tape/deck interaction in one reported case of shedding. My own checks of the same tape with 25
plays per cassette showed absolutely no deposits. Each reader, however, should draw his own conclusions from what happens with his own tape/deck combi nation.
JVC ME and ME-P: The responses for these two excellent tapes are shown in the same figure, and slight adjustments in bias could have made them look just the same. Small differences appear in the table of results, but with just one sample each, there was no proof of which was the better--they both were excellent in every way with the exception of some output level wandering (within a dB) and dropouts up to the audibility threshold.
Memorex Metal IV: This metal-particle entry from a long-time manufacturer of tapes showed smooth, wide responses, very high MRLs and S/N ratio, and low modulation noise. There was substantially no skew in the one sample, and there was no 15-kHz play loss. Flutter was average. The output level stability was good, and there were no significant dropouts.
Osawa MX; This formulation gave another demonstration of the wide responses, very high MRLs, and high S/N ratio that go with metal tape, along with low modulation noise. There was no skew ob served in any of the samples, and there was no 1 5-kHz play loss. Flutter was average. The output level stability was excellent with variations limited to 0.3 dB.
With the analyzer in fast scan-looking for dropouts-the output level was just as smooth most of the time, with just infrequent and sporadic dropouts almost to the detection threshold.
Summary
The general quality of cassette tapes is improving, and a number of those tested this year evidence that fact. Improvements in decks, of course, have been part and parcel of the increasing fidelity possible in the cassette format. Type I tapes offer excellent performance, al though this year's tests indicate the possibility that some formulations might have high frequency losses with repeated plays on some decks.
For Type II in general, ferricobalt tapes gave better frequency responses than did CrO2 on all of the decks tried, but BASF Professional II was a definite exception. There may be decks which are better matched to the non-BASF CrO2 tapes, however. Type III formula lions are still appearing, but the responses remain mediocre at high and low levels. Each new Type IV (metal) tape that is introduced provides another example of a noticeable raising of the DL/MRL curve in the high-frequency region. compared to other types.
(Source: Audio magazine, Sept. 1981)
Also see:
Performance of High Energy in Magnetic Materials in Audio Cassette Recording Tapes (Sept. 1978)
All That Data: Tape Deck Frequency Response and Headroom (Jan. 1981)