Sound and Phonograph We do not have the sounds of our ancestors talking or singing, but some fragments

7.2.3 Sound and Phonograph We do not have the sounds of our ancestors talking or singing, but some fragments

of their music have survived to this day, due to the invention of music notation and symbols, which can be found in cuneiforms from as early as 2000 BCE. They are the equivalent to written texts, and they require special knowledge to decipher the pitch and duration of each note, and whether the music included the harmony of many notes together. The most familiar musical scales repeat the notes at each octave, and the most important scales are the pentatonic (5 notes), the diatonic (7 notes), and the chromatic (12 notes).

Sound involves pressure waves in the air, and the human ear can hear frequen- cies between 20 and 40,000 Hz, or vibrations per second. An instrument such as the flute has a relatively pure sound, where one note consists of mainly one frequency and the loudness of the sound produced depends on the amplitude of the vibrations. An instrument such as the oboe produces a complex sound that is the mixture of many frequencies. A sound recording device must faithfully capture and record all these instantaneous vibrations by frequency and amplitude as they change with time, and be able to play them back with amplification.

The key inventions in the phonograph involve the ability to (a) gather and magnify sound waves, (b) record the vibrations on a durable medium, (c) play back the sound, and (d) reproduce many copies. Thomas Edison invented and developed the carbon microphone, which consisted of two metal plates with a pack of carbon particles between them. When the sound wave hit the front metal plate that acted as

248 CHAPTER 7 INFORMATION

a vibrating diaphragm, the carbon particles became alternately compressed and loosened, so their electrical conductivity alternately became higher and lower. He also developed the first successful phonograph in 1877, by gathering the sound from a large area with a large trumpet, and focusing them onto a small stylus. His recording device was a hand-cranked cylinder wrapped with a tinfoil sheet, and

he used the stylus to cut the vibrations onto grooves on the rotating tinfoil. The frequency and depth of the cutting was controlled by the sound vibrations. The playback was on the same machine, with a needle in the grooves to feel the varying frequency and depths, and to translate them back into sound to be amplified by the trumpet. It was not a commercial success because the grooves wear out after only a few plays, the tinfoil cylinder was difficult to store, and there were no good methods for copying and mass-producing cylinders for the listening public. Many other materials were used for the cylinder later, including a wax-coated cylinder and hard plastic cylinders.

Flat disk recordings became the winning technology, despite the disadvantage that a disk had to run at a constant number of revolutions per minute, so the outside grooves moved faster than the inside grooves. Later in 1877, Emile Berliner came out with his gramophone that had a recording surface made of a flat zinc disk coated with beeswax containing spiral grooves, into which the sound signals were cut at varying widths while the depth remained constant. Berliner’s disk could be copied and mass produced by stamping, and was easier to store than the cylinder. This method led to a separation of the professional recording instruments from the consumer listening devices.

An entirely different method of recording was created by Valdemar Poulsen of Denmark, who made a magnetic wire recording in 1898. Each small domain on the wire could be magnetized to point north or south, and this alternation could be made to code the sound. This led to the later development of recording on the more economical magnetic film and tape. Memory devices were also made with electronic tubes and transistors, which have so many advantages that digital record- ing has replaced analog recording. Today, one of the most efficient methods of recording is the optical Compact Disk, where the sound signals are cut into a plastic and aluminum disk as digital dots and dashes.

Playback of sound recordings was originally done by a large trumpet, which only focused the sound in a specific direction without making it louder, which would be needed for a large audience in a concert hall or public gathering place. Amplifiers were developed to magnify the strength of electrical signals, so that even faint electrical signals could be converted into signals that are 100 million times stronger. Loudspeakers came in to convert electrical signals back into sound waves, often by driving a diaphragm connected to a horn. Reproducing sound faith- fully over a large range of frequencies can be more an art than a science, and it is usually necessary to build large horns for the low frequencies, called “woofers,” and small horns for the high frequencies, called the “tweeters.”

In 1901, Eldridge Johnson founded the Victor Talking Machine Company and began making many famous recordings including the Red Seal records of tenor Enrico Caruso, violinist Jascha Heifetz, and pianist Sergei Rachmaninoff. The

249 world was ready for the synchronized recording of cinema with sound, which

7.2 RECORDS

became the “talkies” that swept away the silent movies.