Surround Sound

Nowadays movie makers make full use and exploit sound technology to tell a story and enable a viewer to experience full visu

Well, times have changed. You used to sit back comfortably in your deep sofa and enjoy your television programs and movies. You could hook up your TV to your stereo system to enjoy stereo sound for your movies. What's wrong with that? Isn't it much better than just sound coming off the television speakers? Well, you might be interested in surround sound which envelops and immerses you in the movie sound. Surround sound makes you feel you are at the scene at the movie experiencing what the protagonist is going through.

Dolby Stereo

Dolby Surround used in movie theaters is called Dolby Stereo. It comprises 4 or more channels. Just like conventional stereo, it has both left and right channels. The third channel is the center speaker channel which is responsible for carrying the dialogue as well as sound effects and music. The final channel is the surround channel which is used to carry the ambient sounds and special effects needed to create a total spatial environment for realistic sounds.

Dolby Surround

With the success of Dolby Stereo in cinemas, it was a matter of time before it made its way into the home in 1982. This comprises of the usual left and right channels as well as the surround channel. A total of three channels. The two surround speakers carry the same signal and therefore the surround sound is in monoaural. There is no center channel and therefore dialogue is not well articulated and defined.

Dolby Pro Logic

It was introduced in 1987 and comprises of 4 audio channels . This is the same set up as Dolby Surround with the addition of a center channel which is responsible for carrying the dialogue content as well as other information. Why do you need the center channel? Well, a person may be sitting in the extreme right can hear only part of the sound coming from the left speaker and vice versa. This is only one optimum spot where viewers can fully enjoy the sound. With the introduction of the center speaker every one gets to the dialogue and other sounds clearly too.

Dolby Digital

The creation of Dolby digital in movies is nothing short of a marvel. Dolby engineers discovered an optimum sound for movies required six channels of sounds. However, the film print lacked space to accommodate all these new information. Using digital audio compression technology, the information is optically encoded in the space between the sprocket holes of the film.

Dolby digital consists of six discrete or independent channels of sound. You have the left and right channel, the center channel, surround left and surround right channel and the last channel carries the low frequency sound and contains only one tenth of bandwidth compared with the rest of the other channels and is therefore the "0.1" in Dolby Digital 5.1

Dolby digital set up is one up from Dolby Pro Logic . Now both the surround sound speakers each have the own individual and separate signal.

What 's so good about Dolby Digital? You really get immerse in the movie. As if you are there. When a plane takes off , not only do you see the aircraft moving from left to right, you can actually hear it too. The sound moves from the left speaker to the center and then to the right. Another great thing about Dolby Digital is that it is digital. That means no leakage of signals from one stage to the next during recording and encoding,

Localisation.

The beauty of surround sound is that it creates a spatial environment. The role of the surround sound is to provide ambient sound and to envelop you as well as to create the spatial effect. In a real environment, a dog barks in front of you. Some of the sound gets reverberated back to you by the wall behind you.

However, there is a problem with surround sound system known as localisation. If we hear a sound coming from the back, we would naturally turn back to the source of the sound. That is not the intention of surround sound. In the cinema we want to focus our attention on the screen in front of us. We do not want to get distracted by sounds coming from the rear or the sides.

How to overcome this problem?

There are two tricks here.

Human psychology is such that we tend to associate the sound where it is first heard. Dolby Surround delays the sound you hear on the surround speakers. Even though we first hear the sound in front and then later in the back, our focus is still in front and we are not distracted at all.

The 2nd trick involves limiting the sound frequency range from 100 Hz to 7 Khz. That means the top 13,000 Hz are eliminated. Sounds above 7Khz are basically harmonics just to allow us to identify the nature of the sound. Also, high frequency sounds are also highly directional. Lastly,

Errors also occur at higher frequencies due to the many times of transferring recording from one medium to another.

Most sounds which human hear are 4Khz and below