Before the digital age, analogue recording was the only option. Acoustic analogue recording is when a small microphone diagram that detects the changes in the atmospheric pressure, or acoustic sound waves. It is then recorded on phonograph, or a medium similar to it, in a representation of the sound waves. The reproduction of this sound is the reverse process. A bigger loudspeaker diaphragm is used to cause the changes to atmospheric pressure and forms sound waves. Analogue recording began in 1857, with a Parisian inventor Èdouard-Lèon Scott de Martinville. Èdouard-Lèon Scott de Martinville invented the phonautograph, which was a machine that could record sounds as they passed through the air, but couldn’t replay them. The phonautograph used a vibrating diaphragm and a stylus to trace sound waves on sheets of paper. The human voice was recorded for the first time by the phonautograph, the recordings were called “phonautograms”. Created in 1877 and patented in 1878, Thomas Edison invented the first practical sound recording and reproduction device, the mechanical phonograph cylinder. The mechanical phonograph cylinder engraved the recordings on the outside surface, then replays them on a mechanical cylinder phonograph. A type of Phonograph record is the Edison Diamond Disc Record, created by Thomas A. Edison Inc.. The record, made of tinfoil, was wrapped around a metal cylinder with grooves and a stylus that was sound vibrated indented the tinfoil as the cylinder was rotated.

The phonograph led to what we now call records. The earliest form of records was called the “Gramophone”. The Gramophone was invented by Emile Berliner in 1889, in the US. The master recordings were recorded on zinc plate disks, then electroplated, and then a negative-image was made from them and used to stamp discs. Initially, recordings were made through all acoustic means. The sound would be collected by a large horn, then piped into a diaphragm, which would then vibrate the cutting stylus. Despite the success with the acoustic recording, in the 1920’s, engineers at Western Electric and Orlando Marsh created a way to capture sound with a microphone. The sound would be captured with a microphone, rather than a horn, which would amplify it through vacuum tubes, creating an electric signal. The vacuum tubes, originally dubbed Audion triode vacuum tubes, created in 1906 by Lee De Forest, were an electronic valve that amplified weak electrical signals. Using the amplified electric signal from the vacuum tubes, an electromagnetic recording head would be driven. Western Electric pioneered the use of mechanical analogs of electrical circuits. They created the “rubber line” recorder for cutting the groove into the wax master in the disc recording system. This started the recording system that is still occasionally used today to record vinyl records. Now that sound had become easier to record, people started to experiment with using it for films. During the 1920s, early motion picture sound systems like Phonofilm used optical recording technology. Optical recording technology is where the audio signal is graphically recorded on photographic film. When playing these films, the film projector used a light and a photoelectric cell to convert the recorded variations back into electrical signals, which were then amplified. The audience heard these amplified electrical signals after the signals were sent to loudspeakers behind the screen.

The ability to incorporate sound into media became easier after the invention of magnetic tape. Magnetic tape recording is when the sound waves vibrate the microphone diaphragm, then are converted into an electric current. This current is then converted to a magnetic field by an electromagnet. An electromagnet makes a representation of the sound as magnetized areas on a plastic tape, this tape is able to do the because of its magnetic coating. Magnetic tape was first invented in Germany by Danish inventor Vlademar Poulsen, and was based off magnetic wire recording. In 1924, Dr. Kurt Stille, developed Poulsen’s wire recorder for the purpose of creating a dictating machine. The wire recorder records things when a wire is pulled quickly across a recording head, which then magnetizes each point along the wire with the intensity and polarity of the electrical audio signal what was being supplied to the recording head at that instant. To play back the recording on the wire recorder, the varying magnetic field created by the wire passing makes a similar electrical current in the head, recreating the original signal. The tape head magnetically manipulates the oxide side of the tape, or the side of the tape that stores the information. Using the inventions created by Oberlin Smith in 1888 and Poulsen in 1898, Fritz Pfleumer, in 1928, created magnetic tape for recording sound. The magnetic tape was first used in 1951 to store computer data on the Eckert-Mauchly UNIVAC I.

The invention of magnetic tape made it possible for the first all electronic sound recording and the first practical commercial sound systems that could record and reproduce stereophonic sound. Stereophonic sound, or just stereo is sound reproduction that creates the illusion of sound coming from different places in the room. Stereo is created by using two or more independent audio channels through two or more loudspeakers or stereo headphones to create the impression of sound coming from multiple directions. Stereo systems can be separated into two forms. The first is “true” or “natural” stereo, where multiple microphones capture live sound. The second form of stereo is “artificial” or “pan-pot” stereo. “Artificial” or “pan-pot” stereo is recorded when a single-channel, or mono, is replayed through multiple loudspeakers. This is achieved when varying amplitudes of the signal are sent to each speaker and artificial direction can be heard. The two recorded channels are similar, but different because they have separate arrival times and sound pressure-level information. This is because each microphone records the separate wavefronts at different times; this leads to the wavefronts being out of phase. All of this creates constructive and destructive interference if both tracks are played back on the same speaker. In fact, the first commercially released film with a stereo soundtrack was Fantasia, released by Disney in 1940.

After magnetic tape gained popularity, the next big creation was the small cartridge-based tape systems, like the compact cassette. The Phillips Company popularized the compact cassette in 1964. Compact cassettes are made up of two miniature spools between a magnetically coated, polyester-type plastic film is passed and wound. A smaller, cooler replaced the vacuum tube, and less power-hungry transistor also accelerated the sale of hi-fi sound systems from the 1960’s onward. These new compact cassettes also use graphic equalizers, where the input is send to a bank of filters. A portion of the signal present goes through each filter and is changed into its own frequency or band. A slide control adjusts the amplitude passed by each filter by boosting or cutting frequency components passed by that filter.

After compact cassettes rose to fame, the next big invention was the compact disk. With the creation of compact cassettes and digital sound recording, the compact disk was created in 1982, and brought major improvements to consumer recordings. With digital recording audio signals picked up by a microphone or video signals picked up by a camera are converted to a stream of discrete numbers. The discrete numbers represent the changes over time in air pressure for audio, and Chroma and luminance values for videos, and are recorded to a storage device. Then, in order to play back the digital sound recording, the numbers are retrieved and converted back into analogue waveforms. The analogue waveforms are then heard through a loudspeaker. The process of this is fairly complicated. The analogue signal is taken from the input device and sent to an analogue to digital converter, or the ADC. Then the ADC converts the signal by repeatedly measuring the momentary level of the analogue wave. Once this is completed, the ADC assigns a binary number with a given quantity of wits, or word length, to each measuring point. The frequency at which this is done is called the sample rate. A digital audio sample rate at a given word length represents the audio level at that moment. This means that the longer the word rate, the more exact the representation of the original wave. The higher the sampling rate, the higher the upper-cutoff frequency of the digitized audio signal. The ADC creates an output of a sequence of 0’s and 1’s in a continuous stream. These numbers are stored in a hard drive, optical drive, or solid-state memory.

By yanam49

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