Copyright Michael Karbo, Denmark, Europe.

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    Chapter 1. Development of sound reproduction

    About sound reproduction

    There is sound everywhere in our surroundings. A part of the sound is reproduction of sound, which are recordings. Recordings are made, for example, while we talk in the telephone, on the radio and on television stations and in record and film studios. All these recordings are reproduced (or played back) all around us in our daily surroundings. We are going to deal with many different forms for recordings and playback in this booklet. We will start in the booklet’s first part by looking at the recording and reproduction of sound.

    Our aim is to understand the particular digital sound, which is found in computers, but before then we have to be able to understand reproduction of sound in a more comprehensive sense. I will start with a little historical summary of the different technologies that have been used for sound recording. We will look closer at what sound, in fact, really is before we delve into the technologies of today.

    Scientists have worked with recording and reproduction of sound (especially music) for about 150 years. During the last 5-10 years the development has progressed particularly rapidly with new formats for digital sound. But if we look back in time, then analog sound formats have actually been changed lots of times. Equally we can see that the entertainment industry has also earlier been hard pressed by technological development – there is nothing new in this.

    Fundamental technologies

    When it comes to the recording and reproduction of sound, then there are a number of technologies that have been developed, altered and improved on all the time.

    These are:

  • The principle for sound reproductions

  • Storage media for recording and reproduction

  • Signal/noise conditions

  • Storage media capacity

    These conditions have reoccurred again and again over the years. The original principle for recording was purely mechanical. Later it became electronic, but continued to be analog. During the last 20 years the industry has continued working with electronic sound reproduction, but now in the light of digital sound.

    Figure 1. The phonograph was the first mass media for music.

    Further consequences of technological development have been big changes and displacement in the entertainment industry. We witness this at the moment while record companies are in a crisis due to, among other things, digital copying in the form of the mp3 format. My point is, however, that there were equally tremendous upheavals during the last century as, for example, when radio and then television appeared in homes. So in one way or another history repeats itself...

    Mechanical sound

    The first experiments with the recording of sound started around 1850. The commercial pioneer was Thomas Edison, who patented his mechanical phonograph, which recorded sound by making scratches in a cylinder.

    The cylinder could afterward be played back in a corresponding machine. The phonograph was used in the beginning especially as a dictating machine but later it became possible to buy music in the form of a cylinder.

    Figure 2. Mechanical dictating machine from 1907. Sound waves are picked up in the horn and transferred to a needle, which makes scratches in a cylinder.

    Flat gramophone records later replaced the cylinders, but recording and play back still took place purely mechanically.

    Figure 3. Record collection in the year 1912.

    Electric equipment

    The Dane, Valdemar Poulsen, developed somewhere around the year 1900 a recording machine which used wire as a storage medium. The wire was magnetically charged ”in time” with the sound waves; the machine was, in fact, a forerunner for the tape recorders, which 50 years later were sold by the millions.  Poulsen’s machine was commercially used as a dictating machine and telephone answering machine.

    At the start of the nineteen-twenties, however, the music industry changed from mechanical to electronic recording, where sound is picked up in a microphone. It is made up of a disk, which captures vibrations in sound and transfers them to an electric coil, which is suspended in a magnetic field. When the coil moves in the magnetic field, alternating current is induced. This alternating current is sound information in analog and electric form:

    Figure 4. The principle behind both microphones and loudspeakers.

    If alternating current is sent inside the coil, which is in the magnetic field, then it will move. When the coil is connected to a membrane, it can produce vibrations in the air; it is in this way that we get a loudspeaker, which is, in fact, the opposite of a microphone.

    Good sound quality

    With the electronic equipment of the 1920’s there was a fast improvement in sound quality. 1930’s Hollywood films (such as ”King Kong” from 1933) gave an, up until then, unheard of sound quality in stereo. At the same time, however, the radio butted in as a sound media and it nearly just about broke the back of the record industry …

    In the following decades, media and sound principles and then video were further developed at a furious pace. Figure 5 gives a short summary:



    Important new technologies


    The war triggers off development in new electronics. Tape recorders break through commercially.


    Grammophone records switch from 78 to 45 revolutions a minute.
    Television becomes a sales success just like hi-fi music centres with stereo grammophones.


    FM stereo radio.
    Philips introduces cassette tape recorders (Compact Cassettes), which become an immediate success among young people.


    Sony ”Walkman”.
    Betamax and VHS video formats.
    Dolby noise reduction for tape recorders.
    Quadrophoni (4 channel hi-fi equipment) was a whopping great flop.


    Dolby Surround (1982)
    Dolby Pro Logic (1987)
    The first digital sound media:
    Sony and Philips audio CDs.
    Digital Audio Tape (DAT)


    Large numbers of digital media:
    Sony MiniDisc and Philips Digital Compact Cassette. In the computer world: mp3, Real, Quick­Time and other streaming formats for sound and video. DV video, webcam, etc.


    Video discs in DVD and VCD formats seriously become a hit. Home Cinema.
    Digital television, video and radio.

    Figure 5. The last 60 years’ development within sound and video.

    What we are seeing, then, is that media for sound and moving pictures have changed a great deal. And because these formats and media play a central role in the entertainment industry, then they have brought about large displacement in this line of business.

    The latest change in the development was the change from analog sound to the digital sound that can be handled by computers. In analog sound systems, the devices work with analog signals like, for example, electric voltage, which varies in time with the music. In digital sound systems, sound is translated into numbers. Later in the booklet, I will show how translation and the interplay between the analog and the digital sound systems take place.

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