Surround Sound Past Present and Future Essay Example

stereo and mono. These systems are known as '4-2-4' systems. However, it is mathematically impossible (Holman 91). Matrix quadraphonic systems have survived in the film industry as Dolby Surround, a development of the more common original systems.

Although surround sound systems can produce impressive auditory effects in the movie theater, they are not ideal for replicating natural soundfields. However, commercial consumer decoders are now available to decode surround-encoded film soundtracks for home video releases. One major issue with traditional quadraphonic techniques involves the limited ability to synthesize spatial localization, particularly when quadraphonic mixes were performed in the studio. Typically, level-based localization was the only method used, usually with quad pan-pots. This approach has already been identified as disadvantageous for stereo listening positions, and this issue is exacerbated for quadraphonic listening as the listener is restricted to a central location amidst the loudspeaker arrangement.

Many recording techniques, especially coincident pair methods, retain various aspects of the soundfield like level and phase data. The difference is noticeable when coincident stereo pairs are combined with mono spot microphones. For instance, when recording an orchestra with coincident pairs, the resulting image possesses stability and the ability to reproduce distance from the listener. In contrast, adding a spot microphone to enhance a solo instrument does not offer those benefits; it creates a straight line between speakers when the listener moves. This stimulated the development of Ambisonics, a UK-made surround-sound system in the 1970s that initially aimed to capture and play natural soundfields in three dimensions with possible height. Nowadays, sound processing tools based on this principle enable engineers to synthesize soundfields in their studios for surround-sound decoding or stereo recordings with

increased depth and image stability beyond conventional localization techniques that only rely on level.

The Ambisonic system is based on Blumlein's stereo recording method from the 1930s. Blumlein used two microphones, one omni-directional to sum the left and right signals, and the other with a figure-of-eight characteristic pointed towards the left to derive the difference signal. The sum and difference signals were then sent to a matrix decoder to produce left and right feeds. Ambisonics expands this technique onto three dimensions. These signals can be created using a "Soundfield" microphone or synthesized from mono or stereo sources with the aid of signal-processing devices during mixing.

The signal known as 'B-Format' holds the necessary data to locate a sound source in 3D space across its four channels. The rise of Surround Sound was promoted through the release of DVD in 1997 and the promotion of "Home Theater." This event has seen technology, aesthetics, and economics all align. DVD technology enables more high-quality sound channels to be accommodated due to its capacity for increased electronic information compared to VHS videotapes.

Surround Sound systems do not have compatibility issues, unlike Quadraphonic. The signal of Surround Sound is encoded so that it can function with mono or stereo systems. This is also aesthetically justified as movies have soundtracks that come from speakers in the front and back of theaters. As equipment prices continue to decrease, more individuals are buying Surround Sound systems.

The availability of programming for surround sound is on the rise, along with the number of releases and broadcasts that feature Surround Sound. Dolby Stereo Digital includes a six-channel digital optical soundtrack, positioned between the film's sprocket holes, in addition to

a four-channel SR analogue track on the same 35-mm print. These prints can be played in any Dolby Stereo cinema, or by adding digital readers to the projectors and a digital decoder that connects with the cinema's existing Dolby Stereo processor. The six channels on the digital soundtrack are configured as Left, Centre, Right, Left Surround, Right Surround, and Subwoofer. This format is identical to the one used for Dolby Stereo 70-mm magnetic with stereo surround but without the costs associated with a 70-mm print or magnetic stripe process.

Additional digital formats have been introduced, such as Matsushita/MCA/Universal DTS (Digital Theatre Sound) and Sony's SDDS (Sony Dynamic Digital Sound). DTS features a 6-channel system that is configured like Dolby Stereo Digital. The digital soundtrack is stored on CD-ROM discs and linked to timecode that is optically printed on the film. Meanwhile, SDDS uses five full-range channels for the screen (Left, Inner Left, Centre, Inner Right, and Right), along with stereo Surrounds and a Subwoofer. Two digital tracks are printed on the outer edges of the film for SDDS.

Both current systems utilize standard Dolby Stereo optical soundtracks, allowing for one print to be suitable for both digital and non-digital equipped cinemas. Bit rate reduction is used by all three systems to compress digital data into the limited space of the chosen soundtrack storage format (Holman 20). There is now significant potential for filmmakers to extend the profitability of their productions through video, cable, and broadcasting rights. It has become customary for feature films to be released on video, followed by viewings on cable and pay-TV channels shortly after release, and eventually - typically in proportion to the

box-office success of the film - aired on public television.

Due to the increased availability and quality of film and multi-channel sound in the home, the consumer hi-fi industry has shifted its focus to the 'Home Cinema' market, offering multi-channel soundtracks that can be transferred to video using an LtRt format. While adjustments may need to be made to the dynamic range, the encoded centre and surround information remains embedded in the 2-channel signal for broadcast or duplication purposes. A Dolby Surround decoder can provide matrix decoding facilities similar to those found in cinema decoders, allowing consumers to enjoy cinema-like multi-channel sound in their homes. Looking ahead, widescreen television is expected to further complement multi-channel sound technology.

The SMPTE has suggested a 5.1 channel standard, which includes Left, Centre, Right, LeftSurround, and Right-Surround wide-band channels, alongside an optional Subwoofer channel for low-frequency effects. This format is currently being used by Dolby Stereo Digital in cinemas. The audio coding employed by Dolby Stereo Digital is AC-3, which will also shape the future of multichannel consumer audio technology via Dolby Surround Digital. In fact, AC-3 has already been chosen as the standard for upcoming HDTV systems in the United States.

With Dolby Surround Digital, it will be possible to convert Dolby Stereo Digital cinema soundtracks to a new home format in a single AC-3 bitstream, instead of analogue surround. To set up basic monitoring arrangements at home, only AC-3 decoding, extra amplifiers, and loudspeakers will be needed. Compatibility is crucial since there are many Dolby Stereo and Surround encoded programs currently available.

The AC-3 consumer decoder can decode 2-channel LtRt and create surround sound through a Dolby Surround Pro-Logic

decoder, ensuring the program is reproduced as intended. However, consumers with less than 5 channels can use the AC-3 decoder to down-mix 5-channel productions to their speaker format. Mixing for multi-channel productions will be similar to mixing for conventional Dolby Stereo or Surround, but with a different encoder and a five-channel mixing console with a master level control. Additional monitoring channels will be required for the stereo surrounds. Multitrack music studios typically record and mix music tracks before transferring them to film for dubbing.

The music studio provides a pre-mix for music, but this may vary if creating a film with on-screen effects or for a musical film. In these cases, a pre-mix would likely be completed at the film dubbing studio. With larger budgets, films can now afford to record their own music rather than rely on library tracks. As a result, music studios will add specific monitors for creating film soundtracks with Dolby Stereo technology.

The SEU4 encoding matrix combined with the reference SDU4 Dolby Stereo matrix decoder allows music engineers to adjust their mix according to how the matrix will affect their sound. Both the encoder and decoder have a 2-track input/output configuration, identical to pre-mixing in film studios. The SDU4 output also features a monitoring section with a 4-channel monitor level control, mono and stereo compatibility check buttons, and a pink noise facility for calibrating acoustic levels to the standard listening level of 85 dB(c) in Dolby Stereo mixing facilities and cinemas. The main difference between conventional stereo mixing for recording and mixing music for Dolby Stereo films lies in the number of monitoring channels available.

To achieve a proper sound

system, it is necessary to install a third speaker as a centre channel. This is because the front stereo information is conveyed through three speakers, not two. Therefore, the third speaker and its power amplifier should match the type used for the left and right channels. If speakers are pre-installed, experts recommend using three separate high-quality speakers and amplifiers temporarily. Moreover, as part of the sound design, at least two additional speakers must be used for the surround channel behind the listeners. There is no need for these speakers to be of high-quality. In fact, the main objective is to deliver a soundfield instead of a specific sound point location, thus necessitating more than one surround loudspeaker.

In order to create a surround sound effect in a cinema, it is necessary to use speakers located all around the walls of the back half of the auditorium. The surround channel is band limited to avoid high-frequency sound that could result in the listener perceiving point sources instead of a soundfield. To ensure that the music sounds the same in the studio as it does in the cinema, it should be mixed with the matrix included in the monitoring chain. It is recommended to mix the stereo 'wide' to prevent a build-up of center channel sound through the matrix. Some stereo generation effects such as synthesizers, chorusing and digital reverberation may cause sound to come from surrounding speakers.

By listening to the matrix, engineers can assess whether desirable effects should be maintained or controlled. The development of surround sound systems has led to the creation of the soundfield microphone which features four capsules arranged in a tetrahedron configuration

within a single casing. These capsules capture all necessary directional information to reproduce a 360° three-dimensional soundfield through a suitable arrangement of four or more speakers. While it has failed to garner significant interest from major record labels or broadcasters, video and film producers have begun producing three-dimensional soundtracks for playback on appropriate speaker arrays. Nevertheless, the soundfield microphone has proven to be an incredibly versatile tool in stereo recording.

The remote-control unit enables the engineer to manipulate the microphone's directivity as well as adjust the stereo width and other parameters, including direct-to-reverberant sound balance, perceived height and more. The ability to control sound with such precision that background noise can be effectively managed was made possible by two paradigm shifts in sound technology – first in the early 1970s and then in the late 1980s and 1990s when digital electronics became ubiquitous. Today, surround sound technology is mainly used in the entertainment industry, and is implemented through various formats (Holman 36). The most widely used format for surround sound today is the 5.1 speaker system.

Common examples of 5.1 Surround formats include Dolby Digital Surround and Digital Theater Systems (DTS). In the context of DTV, it is crucial for digital audio systems to possess innate compatibility with computer-based editing systems, disk-based storage devices, and optical (digital) distribution systems.