written by
Ziga Rezar

Tape types

Tech Gear 5 min read

If you’ve ever taken any interest in tape machines or even just had a good look at all the controls of some of the software emulations, you know that there are different recording tape types in existence. They are some times called “formulations” or “tape chemistry”.

Audio engineers used magnetic tape in all kinds of different audio work. Besides recording the next hit song in a recording studio, they record live shows, play commercials on the radio all day long, archive important conversations or speeches... You get the picture - you can find tape everywhere.

These different tasks required a very different level of performance and price point. Accordingly, recorders were also specialised in the same way and sometimes only worked well with a specific type of tape.

Russian spy pocket miniature tape recorder
Spies used recorders that would fit into the pocket and be mechanically quiet!

To satisfy all those different needs, a number of types were developed and manufactured. A lot of them are still available today! In this article, we will help you understand the differences and similarities between them.

Shopping for tape

You can still find lots of interesting vintage/new-old-stock offerings on various online shops and auctions. This can be a perfectly fine solution if you need a single reel every half a year to bounce a few stems. In the case of mix:analog, we are running a 24/7 online service with more than a single tape machine, so we want something more consistent and reliable for our users.

At the time of writing, two brands of new tape are available reliably - Recording the Masters and ATR Magnetics. Between them, they offer those formulations (click on the links to find out more about them):

Before you delve into the datasheets of each one, let’s first see what are the main properties by which you can compare tape.

Magnetic layers
A cross-section of magnetic tape with various layers that make it

Polyester tape base thickness

Polyester base thickness influences two properties of the recording medium. The first is physical rigidity and consequent longevity, and the second is print-through. Print-through is not so important for bouncing stems like in our use case.

Longevity, on the other hand, is really important! Dozens of users will use the tape each day and the reel has to rewind every 45 minutes of usage! So for our use case, the sturdier - the better! A thicker base tape will absorb more shock and be more resilient.

telefunken m15 tape machine
Telefunken M15 tape machine at mix:analog

Metal oxide coating thickness

Metal oxide coating thickness decides the maximum level that can be printed on the tape. As a somewhat vague example, you could say that the metal oxide coating thickness is like the number of bits per sample of an AD converter. More bits, more dynamic range.

A desirable consequence of a thick oxide layer is a higher obtainable signal-to-noise ratio. But it also means driving the tape bias electronics a bit hotter. This can result in slightly more distortion (depending on the make and model of the tape) but the better fidelity usually outweighs that.

We want ta nice thick layer but not too thick because some of the old tape machines don't have the juice in their electronics to actually print that well on a thick oxide tape layer.

Back-coating tape type and thickness

Back-coating mainly serves two purposes :

  1. open-reel pancake stability - and
  2. static charge dissipation

The additional layer that’s rich with carbon prevents slipping while handling an open reel. This is invaluable in preventing a very probable nervous breakdown if the pancake unravels and you have to put it back together by hand.

open reel tape pancake
A pancake of tape - can you see how quickly it could fall apart?

At the same time, the graphite form of carbon in the coating layer also acts as an electric conductor and prevents the static charge to gather on the tape.

The downside of this additional layer is that more tape dust is produced with usage and it’s possible to develop “sticky shed” syndrome. This can be a problem if you plan to store the reel for a longer period of time.

Which one do we use and why?

First, to minimize the number of rewinds, we choose the longest reel of tape that fits on the deck. That translates to a 1100 metres (about 3600 feet) of tape. That leaves us with three main contenders, the RTM LPR-35, RTM LPR-90 and ATR MDS-36.

Both are strong and modern tapes made to give an awesome performance and long life. The differences are subtle, but let’s take a look:

  • The polyester base thickness is 20𝜇m for both LPR’s and 24,1 𝜇m for the MDS-36.
  • Oxide layer thickness is 11𝜇m for both LPR’s and 12,7𝜇m for the MDS-36.
  • The LPR-35 only has a black color back coating, while the LPR-90 has a back coating thickness of 4,5𝜇m and the MDS-36 has a 0.76𝜇m thick back coating (judging from the thickness also just a thin layer of color).

Considering all of the above, the prime candidates for our use case would be the LPR-35 and MDS-36. The additional back-coating thickness on the LPR-90 might be useful if you’re handling the open pancakes a lot, but any additional dust that could potentially be generated is not desirable.

The tape verdict

Out of the final two candidates, we chose the LPR-35 for reasons that, at least in our minds, outweigh the thicker substrate and oxide layer in the MDS-36.

Recording the Masterst LPR-35 reel
LPR-35, the long-play version of the SM 911

First, the price - the LPR-35 in Europe is almost half the price of the MDS-36.

The second is the delivery format - the LPR-35 is available on a trident reel that’s compatible with both our tape decks - the Studer 812 and the Telefunken M15. The MDS-36 is only available on a NAB reel and that would require an additional adapter and handling to be useful.

Lastly, a vast majority of users use the tape at mix:analog for bouncing whole mixes. That translates into dynamic ranges far lower than those of single instrument tracks, so a dB or two of additional SNR that the MDS is not really useful when compared with the downsides.

If you think we should switch to a different formulation, drop us a line at mixanalog.com and let us know more. We’re always looking to improve our service!

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