Reel to reel tapes info

When reel-to-reel tape was still a studio/consumer product, BASF followed a naming convention that defined the product type. In 1984 it became clear that open reel tape was only going to be a professional product in the future, and the naming convention changed with the introduction of "SM 910"--Studio Master 910. The US market named the consumer products differently, and that accounts for addition confusion. The general run down of products and naming conventions follows.

The product type was first defined by a two-letter designation describing the playing length, followed by a number defining the total thickness of the tape in microns. If the tape were back-coated, an "R" for "rueckseite" followed the playing length. The final letters, if they appeared, described the type of coating.

SP 50 = standard play for 50-micron tape with 1.5 mil base film; 1200' reels
LP 35 = long play for 35-micron tape with 1.0 mil base film; 3600'/1800' reels
DP 26 = double play for 26-micron tape with 0.75 mil base film; 2400' 7" reels
TP 18 = triple play for 18-micron C-60 cassette tape; 15,000' pancakes
QP 12 = quadruple play for 12-micron C-90 cassette tape; 23,700' pancakes
XP 9 = extreme play for 9-micron C-120 cassette tape; 10,800' pancakes

"LH" stood for "low noise, high output" oxide used for better than average performance. "LHL" was a formulation for low printthrough, and "LHS" was an advanced oxide with slightly higher coercivity intended for consumer use at slower 3.75/7.5 ips recordings rather than the more common 15 ips speeds used in the studios. So the SPR50 LHL from the late 1970s was a 1.5 mil backcoated studio tape with lower printthrough than normal.

For the US, the names differed a bit:

Performance = 3600'/1800' reels of LP35 standard oxide
Studio = 3600'/1800' reels of LP35 LHS for slower consumer speeds
Professional = 3600'/1800' of backcoated LPR35 LH for professional use

In the mid 1980s, it was "clear" to the marketing departments that open-reel was dead as a consumer product. In the US, the product managers tossed out scores of unopened boxes of open reel tape into a dumpster. I climbed in and rescued them all for preservation and my own use. The professional group continued to sell the product, of course, and the naming conventions changed to distinguish the use of the product.

LM 920 Loop Master chrome tape in 1- and half-inch width for loop bins
LM 921 Loop Master bin tape with an improved formulation
SM 910 Studio Master tape in widths from quarter inch to 2 inch; 50 microns
SM 911 Studio Master tape with reduced modulation noise that replaced 910
SM 468 Studio Master tape inherited from Agfa; very high coercivity
SM 900 Studio Master tape to compete with Ampex 499 and 3M 996
LPR 35 a throw back to the old naming convention for 1 mil tape

It should be noted that BASF, unlike Agfa, Ampex, and 3M, never used the polyurethane infamous for breaking down over time and causing sticky tapes. I've used a lot of open reel tape over the years, and there is no other tape that outperforms BASF mechanically. Maxell made a great open reel tape; but in published, independent comparison tests for electro-acoustic properties of consumer open reel tapes, BASF was the regular winner. All of the tapes I salvaged years ago still wind perfectly with no significant rub off and no sign of shedding.

The story I heard was that our chemical group refused to use the questionable polyurethane binder, not because of environmental concerns about longevity, but because Agfa-Gevaert held a license for it. They refused to pay Agfa for anything. That's why PEM 469 and 469 had shedding problems and SM 468 and SM 911 / LPR 35 LH(S) did not.

If you're not having a problem with the sample you have and all of the others come from the same lot, then you may have product that Agfa produced with a different binder. They caught on quickly to the breakdown and were one of the first to promote the heat treatment for temporary salvage. I'd keep the tape and watch it closely for awhile. If no problems show up, you've got a great tape.

After we bought Agfa, I wanted to stay with PEM 469 because it was already in use in some studios. The problem was that Agfa had a very small market share compared to Ampex and 3M, and PEM 469 had a reputation sullied by the binder breakdown. We decided to bring in SM 911 and 900 instead and price it slightly below Ampex and 3M. That was the biggest mistake of my career at BASF. No one was interested. Fortunately, no one noticed either. So I changed my mind and raise the price 15% above Ampex and 3M. That's when the studios got curious. (A "cheap" European tape is not interesting; but an expensive Porsche/Mercedes/BMW/Audio image is intriguing--especially when the client, not the studio, pays for the tape.) That's when sales really began to increase. Once 3M dropped out, we had the future wide open--until BASF sold the tape division off and fired all the experienced people.

cassette tape info

A data sheet for a tape has almost all the explanations of tape differences. However, they are hard to understand because of all the curves. Tape experts can judge a tape's electro-acoustic performance from a data sheet and estimate what it will sound like on a machine calibrated for a different tape and know what adjustments need to be made in order to align a deck to the tape described on the data sheet. The only quality parameters not mentioned on a data sheet are mechanical ones: rub-off, adhesion to the base film, stiction, surface polish, and so forth. (If I ever get time, I'll finish the paper on how to read a data sheet.)

1) Frequency response curve--although data sheets are full of curves, those curves represent the effect that bias current has on the output of number of signals at different frequencies. None of the curves is flat. If the sheet shows that a sweep of 12.5 kHz is 6 dB below the output for 315 Hz at -20 dB below the reference level, then the record pre-emphasis must be boosted by 6 dB at 12.5 kHz in order for "flat" response. I have nver seen the type of frequency response curve familiar to consumers on a tape data sheet because that type of curve is reliant on the hardware.

2) MOL is a very important characteristic, but it is offset by noise. Metal tapes have very high MOL values, but they also have poor noise levels. Their signal-to-noise ratios are often little or no better than those for high performance Type II tapes with lower MOL values and lower noise. MOL is a function of magnetic pigment, coating thickness, loading values (ratio of pigment to binder), and uniformity of particles and alignment. The values given in remanence figures correspond to MOL.

3) SOL defines short wavelength output at the point where an increase in input level no longer produces any increase in output because the tape saturates, that is, the high signal level begins to erase the output. This point is hard to define, so greater precision is given when two tones having a frequency difference of 6% are recorded simultaneously and the intermodulation between the two reaches 26.6 dB. SOL values are largely dependent on coercivity. The harder it is to coerce or force a particle to switch its magnetic poles, the harder it is for the particle to self-erase. Type IV metal tapes have the highest coercivity and, therefore, the highest SOL values for cassette tapes. For open-reel tape, SOL is less critical because the higher tape speeds increase the room for wavelengths and dramatically reduce the effect of self-erasure. However, note that "consumer" tapes often show slightly higher values of coercivity because they are designed for acceptable performance at 3.75 and 7.5 ips rather than the studio speeds of 15 or 30 ips.

4) Noise--there are several different measures of noise. Bias noise (a function of particle uniformity and alignment), modulation noise (a function of uniformity of dispersion within a coating, particle uniformity, and surface smoothness), and DC noise (particle shape and distribution). These noises depend on the tape design and processing far more than on any hardware. Chromium dioxide tapes are the best for all of these types of noise because the particle is a "perfect" shape--a long, thin glass-like rod with no external deformities. The shape makes the pigment easy to disperse and align in a coating and gives chrome the low noise values it has. Metal particles, although extremely small and nicely shaped, are very difficult to align because of their enormous coercivity. Coercivity gives metal tape the highest SOL values and excellent MOL values, but those values are reduced by the very high noise levels. For standard oxides, lower noise is a function of the pigment processing to reduce deformities of the particles (often called "dendrites"--Greek for "tree" because the uniformities look like branches coming from a tree trunk) and of the milling process to isolate and evenly disperse the particles within the coating. Ions of cobalt can be added to some standard oxide particles to raise their coercivity at the risk of some instability unless processing steps are taken to reduce the risk of lost remanence from physical forces (the magnetostrictive effect).

5) Uniformity is critical for tape, but what you described is a function of physical stability within a cassette housing, which brings up all sorts of other issue. Tape uniformity can mean two things: A) no deviation from batch to batch; and B) no deviation from beginning to end or from width to width. BASF held very tight specifications for batches of tape so that sensitivity at 315 Hz, for example, did not vary more than +/- 0.5 dB and for 10 kHz more than +/- 1.0 dB for millions of kilometers of duplication tape. This was because duplicators did not want to have to realign equipment for every batch that was delivered for their music cassettes. The beginning of a 23,000-ft cassette pancake should have exactly the same values at the end of the pancake so that the first cassette from the roll should sound exactly like the last cassette.

In studio production, it was even more critical because the sensitivity across a 2-inch width of tape should not vary at all because multiple tracks had to remain in balance. BASF used a knife coating method, and the knife was controlled by a computer that sensed output of the coating and automatically adjusted thickness for uniformity of output. The values of thickness could change slightly through a reel or pancake, but the sensitivity did not. (I believe that Ampex and 3M also used the knife method while the Japanese used gravure coating. Stories about Nakamichi selecting only "center cuts" from TDK production may indicate why BASF/Agfa, Ampex, and 3M produced 1-inch and 2-inch mastering tapes and not the Japanese.

There was a very distinct difference between tapes not only in pigment but also in processing. Now that there are only a few producers making only a few types, the differences are fewer that they used to be.