The Theory of Nothing

How do vinyl records, CD's and DVD's work?

How do vinyl records, CD's and DVD's work?

Now this is a wild ride through history because it demonstrates how we've changed the way we listen to recorded music and watch movies.

In the beginning, man used sheet music and learned how to play instruments such as a piano, violin or a horned instrument. This required the player to learn to read printed music. Then, some genius by the name of Thomas Edison had the audacity to invent the phonograph, a device that could record sounds, including music, and play it back again. This happened in 1877 and resulted in an explosion of interest in music among the masses, much like George Eastman brought photography to the same masses.

A record works by a process of allowing a needle to travel along a grove that makes the needle vibrate according to the original sound that was engraved in the groove. I won't go into the details of the process, but I included it to show you how this concept is mechanical in nature. The signal from the needle or stylus is amplified by amplification--a horn to mechanically amplify the sound at first, and then tube amplifiers to do it electronically, but eventually transistors. Records were around for quite some time as cylinders at first and then discs because they were easier to produce in volume. The record progressed from 78's on shellac to 45's and 33's on vinyl, essentially polystyrene. The number refers to the number of rotations per minute. Obviously, a slower rotation allowed a longer playing record, and that's what the 33's did. This form of music recording lasted until the late 70's when the compact disc came into commercial use. I might add that vinyl records are enjoying a nostalgic comeback along with tube-based amplifiers. Go figure!

Oh, and let's not forget the magnetic tape recordings that paralleled the vinyl record. This idea morphed from reel-to-reel tape, which was expensive, to 8-track, which was at one time popular in cars, to the cassette tape, which supplanted the other forms for quite a while both in the home and car. They have gone the way of high button shoes.

A CD, or compact disc, relies on laser technology, and it radically changed the music industry until just recently when the Internet has made them passé. A CD is a marvel of modern technology and it's a precursor to the DVD and Blue ray discs, which are predominately used for video. A CD consists of a 120 mm disc of polycarbonate that's 1.2 millimeters thick. The recording consists of a series of tiny 1.6-micron pits. On top of this is a shiny layer to reflect the laser light, followed by a lacquer layer protects the shiny layer, and then a top label containing the printing. The master CD disc is recorded by punching pits in a plastic master using a powerful laser. This is used to make a die, which is then used to create copies on softened polycarbonate blanks in a hydraulic press. Strangely enough, the so-called jewel case, the plastic container, is the most expensive part of a CD. The CD can hold up to 800 megabytes of data information, just enough for a typical album.

The CD player, which is a digital device, uses a solid-state infrared laser (780 nm) to read the pits on a CD. The CD format is much more reliable and longer lasting than a vinyl record, and combined with its durability and smaller size, made it instantaneously popular, only recently coming under pressure because of the Internet providing downloadable music.

The DVD is an abbreviation for digital versatile disc. This is the same size (12 centimeters) as the CD but uses much smaller pits--0.47 microns, and thus requires a red laser (650 nm) to read them, which means that a single sided DVD can hold 4.7 gigabytes of data. The main advantage of DVD's is that they can be double layered and hold 8.5 gigabytes of data. What this means is that a full-length movie can be recorded on a DVD in standard video size and letterbox. Both layers are on the same disc and the laser light is focused to change from the first layer to the second.

A Blue ray disc has even more capacity and uses a 405 nm laser that can store 50 GB on a dual layer Blue ray disc, enough to hold a HD video movie.

All of these technologies suffer from the fact that they must rely on a motor to rotate the disc. Solid-state music and movie players like the smart phone don't rely on any moving parts and have become the most accepted method of playing media.

Thanks for reading.