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 December 15, 2005 From Coding to Recording: Audio's Journey Music, like speech, has been an important element of human culture since men and women first began to organize themselves into communities. From the beginning, these forms of organized sound have been used by people to convey information and to stimulate emotions. Music and language played such central roles in society that the urge to preserve them sprang up early, as each generation sought to pass along to its successors both its verbal wisdom and its ceremonial music.The recording medium, to begin with, was memory. Parents taught their children the culture’s lore, both in words and in music, so they could recite or play it to their children in turn -- the oral tradition. What was passed on by this method was the means to re-create the music or the words in each succeeding age; the actual sounds were new each time, dissipating as soon as they were made. Each generation passed along the instructions for performing specific, relatively unchanging sounds, but each time they had to be created anew. The process was made more efficient by the introduction of writing, both of words and of music. Alphabetical and musical notation systems are both types of codes that tell musicians and speakers specifically what sounds to make. Writing had the advantage of being permanent: a long-forgotten document could be understood and acted on, even though the chain of direct transmission had been broken. And writing was relatively insensitive to the condition of whatever it was written on; if a manuscript became soiled or damaged, a fresh copy could always be made, as long as the information on the original was legible. Nevertheless, the speaker or musician reading such a document still had to use the codes it contained to create the words or notes anew. In the aftermath of the Industrial Revolution, a number of inventors sought to remove the human re-creator of sounds from the chain by developing such automatic devices as the music box, the hurdy-gurdy, and the player piano. In these cases, the coded instructions told a machine, rather than a musician, what to play, but the machine still had to create the sounds itself. Such devices were limited as to what sorts of sounds they could make: a player piano could sound only like a piano, not a violin or a human voice. Although such gadgets were popular for a time, what was needed was something that would capture and preserve sound itself, not a written interpretation of it. When an object vibrates, its motion alternately compresses and decompresses (or rarefies) the air around it. Air is elastic; a group of compressed air molecules tends to spring back, compressing the next group of air molecules in turn. Thus, the vibrating object’s vibrations tend to be radiated outward in waves of compressions and rarefactions. At any point in the surrounding area, the pattern of these differences in air pressure will be the same as the object’s vibration, delayed only by the time it took to arrive at that point. When such waves strike an object, they may be reflected or absorbed. Or, because they contain energy, they may set the intervening object in motion, that motion following the pattern of the air’s compression and rarefaction, and hence the pattern of the original vibrating body. The air-pressure differences are said to be analogs of the original body’s motion, and the second body’s induced motion analogous to both. Such fluctuations, whether of air or of solid bodies, have two properties. The distance a body is displaced from its resting position when vibrating, or the pressure difference between a compression or rarefaction and normal air pressure, are said to be their amplitude. The number of such alterations per unit of time is called frequency. If a body vibrates within a certain frequency range, sending a pressure analog through the air, and if the wave hits our eardrums, we hear the pressure variations as sound. The greater the frequency, the higher the pitch; the greater the amplitude, the louder the sound. During the 19th century, a number of scientists and inventors reasoned that the energy in a soundwave could be harnessed to drive devices that would either carry sound over long distances or preserve it in a permanent medium. Two figures in particular can be considered the fathers of audio: Alexander Graham Bell and Thomas Edison. Prior to Bell’s and Edison’s seminal inventions, the need for rapid long-distance communication had been met by Samuel Morse’s telegraph. This had a major impact, as it provided virtually instant contact across a country or around the world, but the telegraph was a very simple device. The sender of a message translated it into a simple code of long and short pulses, which he then tapped out on a key that was nothing but a switch that turned an electrical current on and off. At the other end of the wire, a device made a clicking sound whenever the power was turned on or off; by judging the length of time between clicks, the receiver could decode it into words. Bell’s innovation was a method of replacing this on/off system with one that used a varying current, determined by sound at the sending end. He devised a capsule filled with carbon granules, one surface of which was a membrane that could vibrate in response to sound. As the membrane moved, it varied pressure on the carbon in the capsule, changing its electrical characteristics. Feeding electricity through this now-varying resistor altered the current in step with the variations, resulting in an electrical analog of the original sound. This was the microphone. Edison was more interested in storing sound than in transmitting it over long distances. His device used sound energy to move a diaphragm attached to a movable stylus, which could carve a pattern in a suitable surface, thus creating a physical analog of the sound. A needle placed in this varying groove, and connected to a somewhat larger diaphragm, could reconvert the pattern to sound. Edison’s machine was the first to preserve actual sounds rather than instructions for making such sounds. It recorded rather than coded, and thus revolutionized the accessibility to music and speech from the past. By today’s standards, Edison’s phonograph was primitive. All the energy for making a recording had to come from the sound itself, and all the playback energy had to be contained in the record’s groove. The system was entirely mechanical. Electrical recording became a reality in the mid-1920s, when a version of Bell’s microphone, connected through an amplifier, was used to drive the stylus cutting a record. The amount of power available could now be controlled electrically, rather than simply by playing or singing louder, and multiple microphones could be employed and mixed at different levels. Not long after, the electrical pickup and the dynamic loudspeaker revolutionized recorded music at the playback end as well. While there have been many refinements in the decades since, most of the essentials of modern sound systems date from this marriage of electrical recording and playback technologies. The introduction of electrical circuitry to the reproduction of music, from both the phonograph and the radio, which made its debut as a form of public entertainment in the 1920s, changed forever the nature of home entertainment equipment. What had been a fairly simple acoustical-mechanical device was now much more complex, its parts more specialized. A fairly convoluted process carries a sound from a recording artist to your ears. For part of the trip, the information travels as sound: from a singer’s vocal cords to the microphone, for instance, influenced in various ways by reflections and other physical characteristics of the studio or concert hall where the performance took place. Again, once your loudspeaker has reconverted the material to sound, it is affected enormously by physical factors in the listening room -- speaker positions, room dimensions, furnishings, and the like. All the forces that come to bear when the sound is actually re-created as sound are generally termed acoustics. In between, we speak of audio. It has been said that audio is one of the most "technical" fields most consumers will ever encounter. It lives on specifications and technical terminology, and the buyer who doesn’t have some grasp of how things work and what the words mean is at a considerable disadvantage when it comes to making sensible purchasing decisions. ...Ian G. Masters
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