Audio review: The magic of surround sound
Gatot Tio, Contributor, Jakarta
What makes a surround sound system different from a stereo system? First, a home theater system has more sound channels than a stereo system. Second, in the two-channel stereo, the impression of realism is merely based on soft sonic cues.
In most ordinary two-speaker stereo systems, these subtle cues can easily be vanished, causing the playback to sound flat and "uninvolved".
Multichannel surround systems, on the other hand, can provide this involving presence in a way that is robust, reliable and much more consistent.
Multichannel sound is known as the 5.1 channel system. This is the system which can move a theater to our home. The name 5.1 stands for five channels (in front: left, right and center, and behind: left surround and right surround) of full-bandwidth audio of between 20 Hz and 20 kHz, plus a sixth channel, which will at times contain an additional bass sound to maximize the impact of scenes such as explosions.
This channel has only a narrow frequency response (3 Hz to 120 Hz), thus it is sometimes referred to as the .1 channel. When added together, the system is sometimes referred to as having 5.1 channels.
At present, digital 5.1 sound format is widely used in movie theaters and in home entertainment systems. In the movies, there are three main formats - Dolby Stereo Digital (DSD) by Dolby, DTS System by Digital Theater Systems, and Sony Dynamic Digital Sound (SDDS) by Sony. These three formats are currently used in about 4,000 major movie theaters in the world. The DTS system is used in most theaters. However, the number of SDDS equipped theaters are on the increase now and could even overtake the number of DSD installations within one or two years.
On the home entertainment front, there is only one big name at the moment, and that is Dolby. Here, Dolby's format is known as Dolby Surround Digital. In movie theaters, AC-3 is used in their film sound format, Dolby Stereo Digital. In the home theater, Dolby Surround Digital is also based on AC-3 coding.
In order to enjoy multichannel sound, we must have a surround decoder. This device is used to translate surround sound from the video source -- like a video or TV show -- and then it makes sure the proper sound goes to the proper speaker. This surround decoder usually has built-in audio equipment such as amplifier, receiver and even a player (in DVD player).
An amplifier or receiver can process four to five (even seven) sound channels, then route it to as many speakers as are available.
The system can also provide a myriad of variations on surround sound. They include features like digital signal processing (DSP) which can make your room sound like a cathedral, jazz club or concert hall. Many A/V receivers come with switchable power, which allows the sound output to be directed entirely to the front left and front right speakers for listening to music, or split among surround speakers for home theater viewing.
With the amount of technological advances that are occurring in the field of surround sound, it is no surprise that stereo as we know it will probably disappear. That is the magic of multichannel sound.