[This article can be read without the footnotes, which give additional information and/or provide a level of detail, that may not interest all readers.]
1. The needle vibrated laterally, that is to say: horizontally; in the plane of the groove.
The first recording of Sound in the United States, and perhaps in the world, was made by a device invented by Thomas Edison. The recording medium was a cylinder coated with a wax compound. The recording was cut into the wax by a needle vibrating in response to sound as the cylinder rotated at a controlled speed of about 25 revolutions per minute1. The sound was reproduced by a similar needle riding in the grooves that the first needle’s travel had made. The pattern that had been scratched into the grooves caused the reproducing needle to vibrate, and those vibrations were mechanically amplified2. The cylinder held several minutes of sound.
The next generation of recordings, those that most of us seniors grew up with, were on flat, circular disks having 10 and 12 inch diameters. They provided approximately 3 and 5 minutes, respectively, of music or speech. The underlying principle was exactly the same as that in Edison’s machine, but the flat disks rotated 78 times per minute (78 RPM), and their grooves were traced from the outside edge to the inside. By the time we came onto the scene, amplification was electronic rather than mechanical.
The disks were brittle and, because they were much thinner than the old bakelite cylinders, they broke easily. In the 1930s, the “microgoove long-playing” record”, or “LP”, appeared. The disks rotated at only 33-1/3 RPM but a 12-inch disk could hold more than 20 minutes of sound, not only because of the slower rotation but because its grooves were much narrower than those of the “78”. LP’s would not be widely available commercially until the 1940s, but then they rapidly supplanted 78 RPM recordings.
In the late 1940s, a smaller disk was developed. Like the LP it was made of vinyl, and also had narrow grooves, but it was only 6-3/4 inches in diameter and it had a large central hole. Its rotational speed was 45 RPM. It provided the same recording length as a 10 inch “78”. In both LPs and “45”s, the vinyl material produced much less background (or “surface”) noise than the 78 RPM disks, and vinyl disks did not break. However, they were much more vulnerable to scratches.
The long-playing record remained the standard for commercial sound recordings well into the 1980s, and the 45 remained popular as well.
During that period, a method was developed of recording two channels of sound in one groove, thus making stereo LP’s and 45’s possible3. During that period also, magnetic recording technology was being developed. Recordings made first on special magnetizable wire, and then on flat mylar tape coated with magnetic material, became an alternative technology. Commercial tape recordings were never as successful as LPs, but magnetic tape did prove to be the most practical medium for recording television signals, and video tape cassettes are still used widely to offer movies for rent, although the DVD (see below) is now supplanting it.
In the mid 1980s, the “CD”, based on radically new technology, came onto the market. Its diameter was the smallest yet, less than 5 inches, and like the “45” it had a large center hole, yet it could hold more than an hour of recorded sound. One major departure lay in the fact that the width of the recording path was microscopically narrow, an achievement made possible by the laser. And it was not a physical groove but rather microscopically small markings on the surface. The other major change was that up to that time, all sound recordings sold to consumers contained an “analog” pattern of the same nature as the sound waves that had produced it, but on a CD, the recording consisted of a sequence of numeric “digital” codes4.
Among the superior features of the CD were: uniform sound quality throughout the recording5, almost none of the pops and clicks (referred to hereinafter just as “clicks”) that are universal on vinyl disks6, and freedom from the variations in pitch called “wow and flutter” 7. Furthermore, since the CD is read by a beam of light8, there is no needle to wear down the sound pattern in the CD’s “grooves”. Therefore the CD does not deteriorate rapidly with use. CDs have now almost entirely supplanted vinyl disks in the commercial market, although some vinyl disks are still produced, because many audiophiles insist that the sound on vinyl disks has more “presence” than the sound from a CD9. (Earlier in this article we mentioned magnetic tape recordings. We note here that this medium, too, has begun moving from analog to digital technology.)
A successor to the CD is already on the market: It is the digital video disk, or DVD. A DVD it can contain an entire 2-hour color film with a stereo soundtrack, as you already know if you rent movies at video stores10. It can instead contain several hours of music.
Of course, the DVD is (or rather, was) just one more step in the evolution of recording: The technology is already at the next step, “Solid state” storage: No moving parts, no laser, just electronics. If you have a digital camera, you already use it: The memory card that stores your pictures is a solid state device. And if your children (or more likely your grandchildren) have MP311 players such as the iPod, they are listening to music that is playing from solid state storage. An MP3 player the size of a pack of cigarettes can provide hours of music, which is far more than a music CD, and players that hold even more music are already being sold.
It does not require exceptional foresight to conclude that as the size and expense of solid state storage continues to come down12, that medium will likely come to dominate recorded music, movies and data. Will there be anything beyond memory cards? In a 1970s science fiction film, audiences saw a thin beam of light illuminate a tiny crystal cube, which responded with a voice reading from a vast encyclopedia. We already use laser beams to read CDs and DVDs, will laser-illuminated crystals be the next step in high-density data storage?
W. A. Shapiro
2. The wax cylinders were used as molds for multiple copies made on thick bakelite material, which produced a sturdy recording.
3. The dual-channel recording in a single groove was achieved by making the recording needle vibrate both in the plane of the groove and perpendicular to that plane. Of course, reproduction sensors had to be developed that respond in both planes.
4. Among the many new things made possible by this approach is that CDs can record not only sound but also data and even imagery.
5. The quality of the sound on a 78, a 45 or an LP, is progressively less as the playback needle moves towards the center of the disk. This is because the rotational speed of the disk is constant, so the linear speed of the needle along the groove, which depends on both the disk’s rotational speed and the needle’s distance from the center, gradually decreases along its path. (The slower the linear speed, the less well the higher pitch tones are preserved.) The rotational speed of a CD, however, is electronically controlled by the recording and playback systems to keep the linear speed constant and high..
6. A CD’s “grooves” contain information mixed in with the sound. The additional information consists, in part, of codes that allow the CD player’s electronics to correct for errors including those that would otherwise produce the clicks. In addition, the lack of mechanical contact with a stylus (mentioned later in the article) saves the disk from suffering the little gouges that dust causes when the needles traverses it on a vinyl disk, and that would in turn be “read” by the player as clicks.
7. Wow and flutter are produced by variations in the speed at which the playback sensor moves along the groove. All except the most expensive, professional quality turntables for LP’s, were operated by a mechanical system driven by a simple motor. The motor and other components of that system were subject to significant variations. In CD players, the electronics that control the rotational speed as described in an earlier footnote, control that speed to high precision.
8. The light beam is produced by a laser, which can focus its beam to a spot much smaller than the diameter of the physical needles that are used to play vinyl disks. This is one of the factors that allow a little CD to store so much.
9. Similarly, some amplifiers that use vacuum tubes instead of solid-state circuitry are still manufactured because enough audiophiles prefer their sound.
10. The DVD can also hold much more data than a CD.
11. “MP3” refers to a method by which digitally-coded sound can be highly compressed, so that it takes up far less room than the uncompressed form, at the expense of only a slight reduction in sound quality.
12. and as data compression methods become more and more sophisticated