The 1970s and 1980s were defined by a very particular sound, an almost mythical medium that carried us from our homes straight into the recording studio. We're talking about magnetic tape, which became the mass medium par excellence and gave us access to listening to music on our own and, above all, to recording it.
The turn of the century changed things, and digital music swallowed up the analog market. But now, more than a decade later, analog tape for recording and mixing audio is carving out a new niche in studios all over the world.
Mulann has spotted the opportunity this product offers and didn't want to miss the chance to win back a market that is booming more and more. That's why this French company manufactures analog tape for studios as well as for the film, defense and aerospace industries under the name “Recording the Masters.” What's more, Mulann owns the original patent for the legendary BASF and EMTEC tapes, such as the SM900, which is in high demand among recording studios. So how is blank analog tape made?
Before getting into all the technicalities involved in making this product, we need to clarify a few basic concepts: tapes use low-coercivity ferromagnetic pigments that render all the tonal variations of analog music. Coercivity is the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. For this reason, analog tapes, which are very sensitive to external magnetic fields, dust and fingerprints, must be handled with great care. The manufacturing process is therefore delicate and meticulous. It begins by coating one side of the base, the film, with a thin magnetic layer (about 15μm, where 1μm equals 1/1000 of a millimeter), while the other side is covered with a back coating to give the reel a perfect finish.
To carry out the whole process we're describing, the raw materials involved have to be taken very seriously: powders, liquids, bases and accessories. The powders consist mostly of magnetic oxide pigments, binders and pigmentation that provides color. The liquids used are basic solvents to disperse the emulsion, which are mixed with the binder powders so that the magnetic particles stick to the film base more easily.
In addition, in Mulann's process the solvents, like practically all the chemicals used, are recycled for reasons that are not only economic but also environmental.
The tape bases are rolls of PET polyester film, also known as jumbos, which are bathed in the emulsion. As a curiosity, polyethylene terephthalate, or PET, is an easily recycled petroleum-derived material widely used in clothing and food packaging, so it's not so strange to find it in tape. Depending on the type of film being produced, the base thickness ranges from 7 to 30 μm and the length from 6 to 21 kilometers. Other specific bases are used for magnetic instrumentation tape, since it has to withstand extreme conditions and truly high temperatures.
Finally, the accessories include items as varied as hubs, screws, plastics, metal flanges and cardboard shipping boxes. It may seem obvious, but if any of the raw materials fails or is defective, the entire manufacturing process could be compromised and the final product would not reach optimal quality.
Two different types of emulsion are prepared from the raw materials. On one hand there is a magnetic slurry and, on the other, a back-coating solution. The slurry is prepared by dispersing the magnetic pigments within the binder (in chemistry, a dispersion is a mixture in which tiny particles of one substance are spread throughout another). The binder is made up of small granules that dissolve in the solvent. To achieve a perfect coating finish, various additives are included, such as dispersants, used to separate the pigments; slip agents, which reduce friction between the tape and certain components such as the guides or magnetic heads of recording equipment; and softeners to ensure the coating stays flexible.
Every single tape that is manufactured requires a specific magnetic formulation. That's why, at Mulann, all the raw materials are first “glued” or premixed inside large special drums. Once the solution is ready, it is ground in a special mill. This stage is crucial, since the magnetic properties of the tape are related to the size of the distributed particles. Milling breaks up clumps of magnetic particles, and each particle gets coated with binder. This phase matters because the level of dispersion is directly related to the sound quality and noise of the tape, so the process is measured down to the millimeter and tightly controlled.
Once all these stages are complete, it's time for coating. The emulsion is drawn from its containers, carefully filtered, and a little thickener is added. The mixture passes through a die at a predefined pressure and enters the coating machine. There, the PET film is unwound from its reel, and an automatic system feeds film into the machine in such a way that the end of one reel and the start of the next are spliced together at very high speed.
Once the base is clean, the film reaches the die head, where it is coated with the magnetic emulsion. The whole process is carried out with great precision, since the thickness and length of the coating have to be consistent across the entire film and across all the reels.
Magnets force the magnetic particles into a vertical position, ensuring stability for storing information.
After this, the film is treated with a series of smoothing magnets that realign the magnetic particles in the same direction. Before going into the dryer, while the coating is still liquid, a series of magnets forces the magnetic particles to line up parallel to the tape. This ensures the best recording quality. Next, the film goes through the dryer, that is, an oven containing inert gas from the solvents in the coating emulsion. This step is truly important, since it's the part of the process that gives the tape the stability needed for long-term information storage.
As a finishing touch after the dryer, the calender, made up of several heated metal rollers, presses the tape coating to give it a polished finish. In this way, Mulann ensures that the contact between the tape and the magnetic heads of the recording equipment is optimal. This coating machine runs continuously, allowing new and empty rolls to be swapped without interruption, guaranteeing consistent quality.
Applying pressure to ensure optimal contact between the magnetic heads and the tape
Once the magnetic layers have bonded to the film, the reel goes back through the machine to finish the back side. After that, the drying process starts again. The next stage in making analog tape is slitting the coated reels into tapes of standard widths: 2 inches for 24-track audio recording, 1 inch for 16 tracks, half an inch or a quarter inch. Film reels are also compatible with the 16mm and 35mm formats. The cuts, which are made with extreme precision, require a completely clean, dust-free environment.
Once the film has been properly slit, it is mounted on plastic reels (for the end consumer) or specific reels (for recording studios), depending on its purpose. Finally, every product that comes out of this process is given a perfect finish, from assembly to packaging. All of this is accompanied by constant quality control by Mulann, which oversees everything from the raw materials to the final product.
