Copyright Michael Karbo, Denmark, Europe.


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    Chapter 10. Surround sound

    We have in the earlier sections, looked at analog and digital reproduction of music – first and foremost in the form of ordinary stereo/hi-fi sound. But the really big development lies in the segment multi-channel sound and Home Cinema. Where you can work with several channels of digital sound, which can be compressed and stored in different ways.

    Digital advantages

    Digital sound systems have great advantages compared with the analog. First and foremost, it is much easier to store tracks precisely and safely. If you have a digital version of the music, then it is very easy to distribute completely identical copies. Analog media like LP records and cassette and VHS tapes inevitably lose some of their quality.

    The music industry made early use of digitizing with the normal audio CDs, which replaced LP records. These audio CDs contain a stereo sound with only two channels, right and left. Stereo sound has been used since the 1930s, and within the area of analog sound, it gives the best quality of sound.

    But the electronics industry wanted to make even better systems than those in stereo. With a stereo system the source of sound is usually in front of the listener. If you place several loudspeakers all around a person, then it will give new options for sound reproduction (see also page 3). Due to the development of special multimedia chips for DSP (Digital Signal Processing) in the second half of the 1990s, things got moving in earnest within the digital sound and video industry. These small DSP devices are found today in all DVD players, in sound cards, in mp3 gadgets, etc.  And with them it became possible to create a digital surround sound.

    What is surround sound?

    When you increase a sound system from two to, for example, six loudspeakers, then the sound signals will reach the listener from all sides. This makes it possible to program the sound so that there is a completely different feeling of space. This form for sound reproduction is recognised from cinemas, where loudspeakers are put in many places in the locality and where you can, for example, hear the sound of a train move through the audience.

    For use in the home, surround sound is used for:

  • DVD film with spatial sound (Home Cinema with Dolby Digital, DTS, THX etc.)

  • Computer games with 3D sound in their standards DirectSound, OpenAL, A3D, EAX, etc.

  • Hi-fi reproduction of music of the highest digital quality (with SACD and DVD-Audio).

    The absolutely most widespread of these is seen in the Home Cinema systems, which will probably be used as stereo systems in the home more and more in the future.

    Spatial effect with 5.1 sound

    The most widespread form for surround sound consists of a so-called 5.1 sound which is often illustrated with this symbol:

    There are five main channels for sound plus an extra bass channel in a system with 5.1 sound. The six channels are distributed as below:

  • A centre channel

  • Two front channels

  • Two back channels

  • A LFE channel (Low Frequency Effects).

    The film’s soundtrack is encoded so that the main characters’ speech comes out of the centre channel. The rest of the sound and music is encoded with spatial effect to the four front and back channels. Finally, the LFE channel works either as a subwoofer or for special effects such as earthquakes and such like.

    With a Home Cinema sound system (as in Figure 29 on page 3) you can reproduce the soundtrack of a film with the same effects and the same spatial effects as is heard in a cinema. The system consists of in all 6 loudspeakers, which should be placed in the room as in the arrangement in Figure 54.

    The LFE loudspeaker functions also as a subwoofer so it can be put anywhere:

    Figure 54. Theoretical arrangement of a 5.1 sound system, where the centre channel should be placed near the television.

    Dolby Digital

    The American company Dolby Laboratoriums has worked with professional sound for more than 30 years, and their norms and standards are widespread within the electronics and entertainment industries.

    In 1997, the multi-channel sound system Dolby Digital was introduced onto the mass market (that is to say, all of us ordinary users), and it is used for sound, for example, on absolutely the majority of DVD players. We are talking about a digital and compressed sound format, which can give a multi-channel sound with a quality, which equals mp3.

    The compression principle is called AC-3. It works almost in the same way as mp3 and as Sony’s ATRAC – by removing “unnecessary” data from the soundtrack. With Dolby Digital, the soundtrack of a film can be encoded in a number of qualities – like, for example, 5.1 sound with a bit rate of, for example, 448 Kbps. You can settle for a stereo or mono sound, if the film involved is an old film, which is to be reproduced on DVD. These sorts of sounds are called Dolby Digital 2.0 and 1.0.

    Figure 55.The DVD box always contains information about the sound system. The example on the left has a 5.1 sound, the one the right has a stereo sound.

    Compatibility

    So Dolby Digital sound is encoded with AC-3 and, therefore, is decoded similarly. What is smart with the system, however, is that it is compatible with normal stereo and mono.

    In practice, this means that if you connect a DVD player to an old-fashioned mono television, then all the sound is gathered in a common channel quite automatically, even though the sound is encoded in the 5.1 format. You can also get the sound in stereo. If you have a Home Cinema system, then you will get the full Surround sound. Some players have a circuit called TruSurround, which can encode 5.1 sound into a stereo signal with an artificial spatial effect.

    The big system

    A Home Cinema system can be built up in many different ways. Common, however, for them is the fact that there has to be both decoders and amplifiers/loudspeakers for all the channels:

    Figure 56. The different components that are part of a Home Cinema system.

    A lot is happening within the development of Home Cinema systems in these years. New products are put on the market every week. Most DVD players have built-in Dolby Digital decoders, but require a connection to a surround amplifier, so that the sound can be amplified up to the loudspeaker system. More and more inte­grated systems are coming onto the market, which will probably be one of the big sales successes in the coming years. Her e you can get lots of functions built together in the same box:

  • DVD player with med Dolby Digital.

  • 5.1 surround amplifier set.

  • FM radio.

  • Complete loudspeaker set.

    An integrated player like this can work both as a DVD and stereo system, but can also play normal CDs, mp3 files and much more. The only thing missing is that manufacturers can find out how to build in a MiniDisc.

    If the system also includes a complete set of loudspeakers, then we are talking about a Home Theater In a Box (HTIB) (see Figure 29 on page 3). The biggest problem with these complete sets is that the loudspeakers are not always of a good quality and that is a shame. Because, with good loudspeakers, a Home Cinema system could both be a compact and a versatile hi-fi-system with a high-class sound.


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