How is video recording even possible? More specifically how can changing the magnetic polarities of microscopic metal particles, bonded to a thin ribbon of tape, store knowledge, sound and video? In this opening section we are going to explore just the basics of how this is possible. It really is a fascinating story. One involving something that can't be seen, smelled, tasted or heard and isn't even fully understood, magnetism (and electricity). The discovery of electricity only happened very recently in human history, but it has always been around. Only within the last 150 years or so have we begun to understand some of it's properties. It's staggering to try and comprehend all we already know on this subject so we are only going to concentrate on just the part that deals with the electromagnetic storing of video and audio. It sounds complicated but it is really easy to understand and fun to know, so let's take the plunge.
Video recording is possible because of one of the smallest things in the universe, the atom. On the right side of the above graphic (PLATE 1) are three illustrations that represent an atom. No one knows exactly what they look like because they are too small to see. But by using indirect observation, mathematics and informed speculation we humans have decided how they should look. We also know a lot about how and why they behave the way they do and most of what they are made of. But we are still blowing them apart to find the smaller and smaller particles that make them up. (Is the Higgs Boson really the smallest particle?)4 Here we are only going to concern ourselves mainly with the electrons. They are shown as yellow balls with the minus (−) signs on them. They spend much of their lives held in place by the positively charged protons located in the center mass called the nucleus. The protons are represented by the plus (+) signs on them. They hold the electrons in a spinning circular orbit similar to the way the earth is orbiting around the sun. It is the number of protons in the nucleus that determines the weight, type of element and its characteristics. The number of electrons usually matches the number of protons. But the electrons are not permanently locked in their orbits and can move about under certain conditions or when enough force is applied. This ability to socialize gives electrons some very interesting capabilities. Like carrying electricity, holding a charge and creating magnetism. Electrons reside in orbits (also called shells or clouds) and kept fairly stable by the nucleus. It has been determined the shells want to hold a specific number of electrons to reach a state of electrical neutrality or balanced charge. If they don't have complete shells then that atom is looking to steal some from somewhere to complete their shell and get neutral. To do this they join up with other atoms. Electrons are shared in this way and the result can be a marriage with another atom of its own kind to form an element or with a different one to make a compound. The first orbit out from the nucleus (called the K orbit) wants to hold only two electrons. This is neutral atom is Helium. Any atom that has shells that are complete is an inert gas (also called a noble gas). The second orbit (or L) wants to hold eight to be happy. Once again it is neutral and is a noble gas called Neon. These atoms readily conduct electricity but they don't usually combine with other atoms to make compounds. They don't even mate up with their own kind. They don't need to borrow electrons from other elements to complete and neutralize their orbits. There aren't many of these noble gases. All the other elements known to exist have outer shells with orbits that are incomplete, so they want to get together with the other elements to share electrons. This joining of dissimilar elements happens during a chemical reaction and it results a totally different material than the two originals. A typical example of this is  where two hydrogen atoms (a gas) and one oxygen atom (also a gas) have bonded together to form water (a liquid at room temperature). These atoms are sharing electrons to complete their shells. They have formed a compound (and compounds can be made up of many elements all sharing electrons to get to a neutral state). Wow! Relax, this is as far as we go with the chemistry lesson, but If you want to see a great interactive chart of all of the atomic elements (called the "Periodic Table"), click here.
1The Brout-Englert-Higgs boson, or so called God particle, is an elementary particle discovered by colliding protons at enormous speeds in CERN's Large Hadron Collider. It's discovery could open the way to the understanding of how atoms acquire mass and in turn produce gravities embrace.
Compounds usually are pretty stable when joined in this way because their electrons can easily move around on each other and completing their shells. But electrons can get knocked out of their orbits as they spin. All it takes is for a little outside energy to enter the picture. For example when two clouds (moist air masses) rub against each other they create friction, which is a form of energy. This action can knock around a bunch of electrons. And when enough electrons get loose and roam out of their orbits they can pile up in one place. This creates a very large negative charge with electrical potential. Nature likes everything to be neutral and "in balance" so at some point that negative charge is going to want to find a positive one. Enough charge and a massive discharge occurs. Lightening is a perfect example of electrons moving very violently from the ground or between clouds in an attempt to bring opposing charges back to the neutral state. This is illustrated above on the upper right. (The earth is huge compared to the size of the atmosphere and it can absorb a lot electrons.) This electrical action constantly goes on in some form all over our planet. This is because our atmosphere is always on the move creating massive mountains of electrons. THIS A VERY GOOD THING! Another way to store up a charge of electrons is to rub your feet along the floor and then touch a door knob to release it, as illustrated below the lightening. This wandering nature of electrons can be controlled and when they are harnessed a lot of good can come from it. In fact, life would probably not be possible if it weren't for the harnessing of electrons. (Of course all the subatomic particles are important but the electron is the major player.)
But friction is not the only way to get electrons moving. Chemical batteries can release electrons through a process know as "the breakdown reaction". Here metals and compounds are used that like to give up electrons when requested. These compounds are electron rich and when they react electrons are released. The sun can also force electrons to move in certain types of atoms when light strikes them. Solar panels are an example of this. But by far the most useful and controlled way to get electrons moving is by using an electron generator. Power plants are giant electron generators. They make electrons move by passing a magnet over a wire. Click on the graphic above and lets see why and how this happens (PLATE 2).
With electron theory behind us we are now going to concentrate just on electricity and magnetism and what great benefits they give us. First off everything conducts electricity to some degree (that is to say the moving of electrons from one atom to the other) but some materials are better at it than others. Atoms or compounds that freely let electrons hitch a ride over their outer shells (with little resistance) are called conductors. Atoms or compounds that resist electron movement are called insulators. (Please examine the above illustration.) Notice the green insulation around the wire. Also take note of the red circles with arrows that represent a magnetic field. Inside the insulation is a wire made out of a metal that conducts electrons very well. In this case it is copper. Shown also is the direction in which the electrons travel in the conductor from one end to the other while making the charge neutral. This wire encourages electrons to follow in a specific path without wandering off. (Electrons like taking the path of least resistance… but don't we all?) If the conductor is good at passing electrons and the insulator is good at keeping them in line the electrons can be sent over great distances without the majority of them getting lost along the way. I am setting the ground work here for some interesting phenomenon. But before I go there let's look at what goes on with a conductor on the atomic level, shown at the top and lower left. The reddish colored balls represent copper metal atoms, their orange centers are the nuclei and the yellow dots are the electrons (with the negative signs on them). Air would be the insulator in this case but the illustration is mainly for showing how electrons hop from one atom to the other (see the curved black arrows at the very top of the row of reddish atoms). They don't have to travel the entire length of the wire all at once. They only have to jump the length of an atom. During conduction that happens very fast. (The insulators transfer rate, in this case is air, for electron travel is very slow.) Not at all would be ideal. The only requirement in this little game is that the same number that goes in on one end has to come off at the other (only theoretically because some would get lost due to resistance and heat, no conductor is perfect 2). All you have to do to get electrons flowing is to create what is called a circuit. Technically you would provide electrons at the negative end of a wire to feed a hole at the other end called the positive charge (or well). Do this and electrons will happily travel along from one end to the other until you stop feeding it electrons. As long as there are electrons being added at the negative end and being removed at the positive end they will create a current. Also as the electrons jump across the atoms they emit a pop of external energy, Something we call magnetism. It can be used push and pull at metals, send waves, and more. Plus these electrons can be store for later use using the right materials. Electrons, gotta love 'em. We have something great here… and we are going to put these little buggers to work for us. The magnetic field is illustrated above as pulsing out around the green insulated wire. Fortunately, magnetism has no problem penetrating the insulation. The only barrier for it is distance. I say fortunately, because when you wind an insulated wire around a material that can absorb the magnetic field some really good things start to happen. Wrap it around a bar of a suitable metal, such as iron, steel or nickel and it can make motors, transformers, electromagnets, relays and a whole list of other electrical gizmos. It is the electrons that do all the heavy lifting. But they do so much more than grunt work. We have figured out through experimentation that we can make them do almost anything. We are only limited by our imaginations. Now would be a good time to take a break, get some refreshments and when your ready, we'll discuss how magnetism rocked our world.
2Check out the fantastic world of "super conductors" by searching the internet.
Up to now we've talked about electrons only going in only one direction, minus to plus. This one way movement of electrons is called direct current, or DC and it is very useful and necessary in our daily lives. But there is another type of conduction method is called AC or alternating current. It uses the same electrons but this time they don't go from one end to the other but they just jump back and forth between the atoms. This is done by having the polarity on each end of the wire to cycle or oscillate from plus to minus. With AC the hole or well now alternates back and forth between the two ends of the wire. The electrons now just have to travel back and forth between its neighbor, and only the width of the atom. This action produces some characteristics the DC current can't duplicate. The shorter traveling distance produces less heat with fewer electrons lost. And since they don't have to move very far AC can travel greater distances more efficiently than DC. Plus the alternating magnetic field creates some outstanding possibilities because it too cycles back and forth as the current changes direction. This changing magnetic field can be used to transfer current from one coil of wire to another coil when the two are wound together. This phenomenon allows the creation of transformers that can supply several different voltages from only one input. The ratio of the primary coil winding to the secondary coil or coils in the windings makes this possible. Pretty nifty. So now let's explore the magnetism created from making the electrons move and let's use it for doing something specific, like making magnetic recordings. You knew this was where I was heading. Click on the picture (PLATE 3).
As mentioned earlier if a wire is looped in a coil around a suitable metal, such as iron, and DC current is passed through it a magnet will be created. The moving electrons will cause the atoms in the iron to line up in a special way that generates magnetism (as the electrons pass through the wire). Iron isn't the only element that has this ability, but it's just very good at it. Many metals are (magnetically) polar and have what is known as opposite instances from one side of an atom to the other. Some metals can retain their magnetism almost permanently, but others will revert back to a neutral state when the electric current is turned off. The ability of some metal compositions to switch magnetism rapidly is especially useful for things like relays, solenoids and recording heads. The faster they can be cycled the higher the frequencies that can be realized. Magnetic attraction is different from the atomic attraction between the electrons and protons. For one thing the two poles of magnetism don't cancel each other out, both the negative (called the SOUTH pole) and the positive (NORTH) are always present3 and one pole can't be stronger than the other. The attraction force of a magnet is called its field (also lines of force or flux). A representation of this field is shown in the upper left of the illustration above. A number of metals such as iron, steel, chromium, nickel and others are attracted by this magnetic field. When in the presence of the field the metals provide a path for the lines of force and also become magnetic. Everything in nature is influenced to some degree by magnetism but the ferrous family of metals (see the periodic table of elements) are especially affected. Another important trait of magnetism is that if a magnet is passed by a coil of wire the electrons in the coil will be excited and create electricity. This generated electricity can be used for a lot of things powering cars, or homes and to send to an amplifier for the playing back of previous recordings. As you can see in the illustration the shape of the core metal doesn't have to be straight. It can be formed into various shapes and the lines of force (and the two poles) will follow it. In the lower right it is shown being shaped into a "U" shape. The opposing poles can be brought very close to each other. When this is done the resulting air gap between the poles results in a very close and very strong magnetic field that can be specifically shaped and easily controlled. This "U" shape magnet is used in magnetic recording and is commonly called the recording head, pick up or coil. This tiny gap, shown as the radiating rings of white, is where the magnetism is transferred to a ribbon of tape4 for use in video and audio capture. During recording a moving strip of film with microscopically fine iron particles bonded to it is passed next to the gap. When the magnetic field is varied in strength a pattern of the fluctuations is recorded or stored by the metal bonded to the tape. This stored pattern can be read if it is passed over the same or similar "U" shaped magnet during what is called playback. This is a pickup or passive response. The magnetized particles will cause an electrical field to be generated in the magnet now being used for playback. This happens because when the magnetized particles passing by the now "passive" coil generates an electrical pulse in the wires wound around the metal. These electrical pulses can be used to read the information stored on the tape. This is the way almost all magnetic recording is done. So now that we have the atomic, electronic and magnetic process down let's look at the interesting way iron (or other magnetic alloys) are bonded to a ribbon of film so they can be used for magnetic recording. Click on the illustration again (PLATE 4).
3This has recently been revised. Check out the strange world of the mono pole magnet by searching the internet.
4This also applies to magnetic disks, drums and a myriad of other storage devices.
The process you see above is used, in one form or another, to make all kinds of magnetic recording media. That includes hard drives, floppy disks and recording tape. Looking at the illustration we see that finely ground and shaped metallic particles are mixed with solvents, binders and encapsulated lubricants in a big hopper. From here it is precisely applied to a long thin sheet of film called the substrate. (For hard drives it is applied to a disk.) The magnetic particles are passed through a magnetic field so they are aligned to be in a neutral (or scattered) state and then heated to bond it to the surface. It is engineered to be uniform and to remain permanently attached. (Lubricants are not used in memory disks, hard drives, etc.) The film is then cooled, cleaned and then polished a number of times to make it smooth and uniform. It is then slit and wound upon large rolls (called pancakes) for loading into video cassettes. Now that we know how recording tape5 is made let's bring it all together to see how we can use it store and retrieve information. Let's go to the next graphic (PLATE 5).
5Using magnetic particles bonded to a substrate is the most common method for making audio recordings but early on other methods were experimented with. Since many metals hold magnetism in the next section you are going to see a device that recorded audio using a spool of wire.
From the illustration above you can see that what is going to be recorded is being picked up by an electrical device, in this case it is a microphone. To keep this simple in this example we are only concentrate on sound recording. Video is similar only the mechanical method is different (more on this later). The sound waves traveling in the air hit upon the internal components of the microphone. It is a coil attacked to a membrane that vibrates around a permanent magnet This generates a small amount of electricity. This variable current when amplified can be used to record, transfer data or cause a specific action to take place. In this case the current is being used to create a current to generate a field in a recording head. Recording is illustrated in the lower left in the above graphic.
The method goes like this. (Referencing PLATE 5) The physical movement from a sound waves makes electrical pulses in a pickup device, in this case a microphone. A processor sends this to the recording head that produces waves of magnetic force in the tiny air gap near the tape (shown as white rings). Passing a recording tape by this gap at a uniform rate produces a pattern, or magnetic signature along the tape (shown as north and south or "N S" in the picture). The magnetic force aligns the iron particles in such a way that they will remain locked in a stable position until they acted upon again by another field during some later recording event (this process can be done over and over again). To access the pattern the tape is rewound and passed across the same head for playback. Now the head is passive and becomes a pick up device that reads the information stored on the tape. The magnetized particles in the tape now generates a small electrical current in the passive head as they pass by it (this is called induction). In the case above electrical pulses are amplified and made to flex a moving cone of a speaker to reproduce sound that resembles the original source. To do this the speaker has a wire coil located near a permanent magnet attached to a flexible cone. It vibrates and creates the sound using mechanical waves of force. Simply put we have sound going into using a microphone, it's converted, passed on to an electromagnet and saved to magnetic particles on a tape. The tape is rewound, passed over the head again for playback, it's converted and amplified so the sound that was recorded earlier comes out of a speaker. There you have it. Now, there are many factors that can affect the quality and strength of the recording and we're going to look at some of these now. I'm headed somewhere important with this so keep reading, grasshopper (PLATE 6).
One of the major factors that affects tape recording quality is the speed (or rate) of the tape travel. The faster it goes by the head the more information can be stored during a given time frame. The larger the area that goes by the more particles to store the information. But there is a physical and practical limitation to this. Too fast and friction causes things to heat up, wear increases and the mechanical components start to move too fast to be practical. Too slow and quality goes down because of fewer particles going by. To help offset this problem tape manufacturers make the magnetic particles on the tape very small so they can hold more information. Making the gap smaller on the heads also helps. But there are physical limits. Look at the picture above and you will see three charts (PLATE 6). The speed of tape travel is shown here as inches per second (IPS, CMS or centimeters per second is also used). The squiggly line going across these graphs is the frequency response (how much force the atom particles will hold before they can't hold any more). What you're looking at is a graph showing the physical limits of tape verses speed as it applies to the recording capability of magnetic tape. These charts are for sound recording and as you can see when the tape that is going by at 7 1/2 IPS in the chart at the bottom shows that the higher frequencies of 30,000 cycles and above are being lost (cycles is also called Hertz in honor of a famous scientist so the expression 30 kHz or 30 kiloHertz is usually used). They are simply being lost because not enough particles are passing by (and taking their maximum charge of magnetism) in a short enough time to register these higher frequencies on the tape. There is only so much magnetism that can be imparted into a specific media. Lots of different formulations and processes are used but every one has a limitation. So to overcome this limitation we crank up the speed. Now look at the 15 IPS in the middle, twice as fast, and we start to see that much of the higher frequency is getting recorded. Twice as many atoms are going by per second, but the very highest frequencies are getting weak. At 30 IPS it gets better, but as stated before, there is a physical limit. Why are high frequencies harder to record than the low ones? The highs are vibrating very fast (cycles) and require more particles to be magnetized for recording. Lows are large, vibrate slow and are easy to record. Sound is one thing but recording the high frequencies needed for recording video are beyond the capabilities of the linear (traveling by the head in a straight line) method shown here. But we have laid important groundwork, so read on.
So far we've concerned ourselves with audio recording but things get really dicey when you try to record a signal as high in frequency as video requires. Click on the picture (PLATE 7). 50,000 cycles per second is about the highest audio frequency a human can hear and about the limit that audio tape can record. So standard linear recording works pretty good for audio. But the vibrations required to make a video recording is in the range of 650,000 to 8,000,000 cycles per second (8 MHz). Wow! How do you record such a high frequency? You can speed things way up. In the first attempts at video recording that is just what was done. Tape reels as big as barrel heads held tape that traveled by the recording head at over 160 inches per second. This could record a thirty minute stretch of video. But it was impractical. The recording head became so hot that it had to be physically cooled. No telling what would happen if the tape broke during on of these sessions. A better way needed to be devised. In the picture you can see the computation used to arrive at 160 inches per second for linear video recording. There isn't any problem with creating magnets that reproduce frequencies high enough but putting them on to a recording medium (in a practical manner) is. To overcome the size and speed issue a new system of recording was developed for video. Click the picture to see how it is done (PLATE 8). The ingenious answer is to spin the recording and later, playback, head(s) at high rate of speed. Now the recording head moved very fast and the tape could travel by at a reasonable speed. The heads could also be made smaller and any heat was carried away by the tape. This system allowed for a high writing rate and provided the frequency response needed for video. This method is called scanning and it is the backbone of most video tape recording. In the picture you see the two types of scanning methods. At the top is the vertical (edge to edge) system. While this system is good and allows for a lot of signal to be recorded it isn't practical for things like home recording or portability. While the tape traveled at a reasonable speed it was two inches wide, and the reels were still pretty big, so this system found it's way mostly into the broadcast industry. The bottom illustration is the longitudinal (going long ways) method of recording. It has a tape speed similar to audio and still will allows a high speed video track to be placed on it. The obvious advantage here is the tape, reels and the machines can be a lot smaller. This is the system that eventually became the standard for most video recording.
Now, that wasn't very hard was it? And we covered a lot of ground. But I bet you already knew most of this already. So next we look at how this longitudinal (long ways) scanning system was first adapted for broadcasting and then how it eventually made it's way into your home. Before we go to the next panel I want to answer a question that might be on your mind. How do you get a current to a spinning electrical part without there being a dedicated connection? It is possible due to a phenomenon know as coupling, which is very similar to magnetic recording. A pulse of current is introduced to a flat coil (called the primary) that is in close proximity to another flat coil that is passive (called the secondary). Current introduced into the primary is transferred to the secondary. It works in reverse, too. This is also how a transformer works and this is why the spinning heads of a video drum do not have to be hard wired. If you would like to see this neat arrangement click on the picture one more time. To go to the panel on reel-to-reel recording click here.
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