DOLBY

W H I TE P AP E R

HCL Infosystems Limited

Contents

Dolby Executive Summary................................................... 3Major Specification... ................................................. 3Benefits of Infrared ...................... ............................ 3Basic IRDA Usage Model......... ................ ................. 3IRDA Implementation in Computer Systems................ 4IRDA Devices............. ............ ............ ............... 4IRDA Limitation............. ............ ............ ............... 4

Dolby Technology Explained............. .................................. 5Introduction ...................................................................5Infrared Basics ..................................... ........................5Infrared in Consumer electronics ..................................6The IrDA standard ..................................... ...................6IrDA-Data Architecture and Protocol Stack - Overview .7IrDA-Data Architecture and Protocol Stack - In detail ...8Infrared Q & A ..................................... ........................10Reference ...............................… ... ........................….12

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Overview of Dolby Technologies

1. Introduction 2. Analog Recording Technologies

o A-type NR o B-type NR o C-type NR o Spectral Recording (SR) o S-type NR o HX Pro

3. Digital Audio Coding o AC-1 o AC-2 o Dolby Digital (AC-3) o Dolby E o MLP Lossless o AAC

4. Film Sound o Dolby Stereo o Dolby SR o Dolby Digital o Dolby Digital Surround EX

5. Consumer Surround Sound o Dolby Surround o Dolby Surround Pro Logic o Dolby Surround Pro Logic II o Dolby Digital o Dolby Headphone o Dolby Virtual Speaker o Virtual Dolby Surround and Virtual Dolby Digital

1. Introduction

Dolby Laboratories' core technologies, both analog and digital, are signal-processing systems that improve basic sound quality, and/or enable multi-channel surround sound in applications such as audio- and videotapes; movie soundtracks; DVDs; computer and video games; and TV, satellite, and cable broadcasts. Some Dolby technologies are incorporated into professional audio products, including cinema sound processors and digital audio codecs that are manufactured by Dolby Laboratories. These are used worldwide in recording and postproduction studios, broadcast facilities, cinemas, and tape and disc duplication facilities.Other Dolby technologies are licensed to manufacturers of consumer products such as cassette and DVD players, home theater systems, PCs, and set-top boxes. These technologies are implemented on integrated circuits (ICs) developed in close cooperation with Dolby by leading IC manufacturers, who make them available to Dolby licensees for incorporation into their products.

2. Analog Recording Technologies

Beginning with A-type noise reduction, Dolby Laboratories has developed a family of processes that improve analog recording media without audible side effects on the material being recorded.

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Dolby noise reduction is a mirror-image, encode-decode process used both when a recording is made and when it is played back.

A-type NR, introduced in 1965, was Dolby Laboratories' first innovation. It was originally intended for use by professional recording studios to make quieter master tape recordings. In the early 1970s its use was extended to film studios and motion picture release prints to improve film sound.

B-type NR is the original Dolby system designed for consumer tape recording. More than 30 years after its introduction, it is still included in all but the least expensive cassette recorders and players, and is used in the preparation of almost all prerecorded cassettes.

C-type NR was developed later to provide twice the tape hiss reduction of Dolby B, and introduced further innovations (spectral skewing and antisaturation) for better cassette performance. Today it is included along with Dolby B NR in many low- and mid-range cassette units.

Spectral Recording (SR), Dolby's second-generation professional recording system, was introduced in 1986. More than a noise reduction system, it extends the overall dynamic range of analog media to rival or surpass that of digital formats. Today the analog soundtracks on virtually all 35 mm movie release prints are recorded with Dolby SR.

S-type NR, the highest-performance Dolby system for analog cassette recording, is derived from Dolby SR and shares several of its advanced features. It is included in mid-range to high-end decks that can record cassettes rivaling CDs in quality.

HX Pro is a cassette recording technology that makes it possible to capture loud musical passages with fewer high-frequency losses and less distortion. In addition to being available in many cassette decks, it is widely used in the recording industry to improve the quality of prerecorded cassettes. Dolby HX Pro is a record-only process, and requires no playback decoding.

3. Digital Audio Coding

Based on research into human hearing, the sophisticated algorithms used in Dolby's digital audio technologies make it possible to store or transmit digital audio using less data than would otherwise be necessary.

AC-1, the first Dolby digital audio coding system was introduced in 1984. A refined form of adaptive delta modulation, it was intended for applications such as direct broadcast satellite systems at a time when digital signal processing "horsepower" was very costly. AC-1 featured a comparatively complex encoder, a relatively few of which would be needed by broadcasters, and simple, inexpensive decoders that could be readily incorporated into mass-produced consumer receivers.

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AC-2 is an adaptive-transform-based algorithm that combines professional audio quality with a low bit rate, substantially reducing the data capacity required in such applications as satellite and terrestrial links. The algorithm uses a multi-band approach to take advantage of psychoacoustic masking, while a partially adaptive bit-allocation scheme keeps codec complexity relatively low. It is used by recording studios and postproduction facilities for such purposes as remote monitoring and dialogue rerecording (looping) sessions.

Dolby Digital (AC-3), Dolby's best-known digital system, is used to provide multichannel surround sound in cinemas from 35 mm film, and in the home from laser discs, DVDs, and digital broadcast television, cable, and satellite systems. It enables the transmission and storage of up to five full-range audio channels, plus a low-frequency effects channel (LFE), in less space than is required for just one linear PCM-coded channel on a compact disc. Additional features include the transmission of metadata that can control playback parameters such as dialogue-keyed playback level, and the ability of two-channel decoders to downmix multichannel soundtracks.

Dolby E is a professional audio coding developed to assist the conversion of broadcast and other two-channel facilities to multichannel audio. It allows an AES/EBU audio pair, or a single pair of digital VTR audio tracks, to carry up to eight channels of broadcast-quality audio for postproduction and distribution. Among other benefits, Dolby E encoded audio can be edited, decoded, and re-encoded many times without audible degradation.

MLP Lossless is a true "lossless" coding system specified for DVD-Audio that compacts PCM data with bit-for-bit accuracy, unlike "lossy" perceptual coding systems such as Dolby Digital. MLP Lossless effectively doubles disc space without affecting the quality of high-resolution PCM audio, making it possible for DVD-Audio discs to carry both stereo and multichannel mixes of the same program. All DVD-Audio players are equipped with MLP Lossless decoding, while its use on the discs themselves is at their producers' discretion.

Advanced Audio Coding (AAC) is high-quality perceptual audio coding technology appropriate for many broadcast and electronic music-distribution applications. Coding efficiency is superior to that of MP3, providing higher-quality audio at lower bit rates. Developed and standardized as an ISO/IEC specification by four industry leaders (AT&T, Dolby Laboratories, Fraunhofer IIS, and Sony Corporation), AAC is supported by a growing number of hardware and software manufacturers as the logical successor to MP3.

Overview of Dolby Technologies

4. Film Sound

Dolby Stereo, introduced in 1975, was Dolby Laboratories' first major contribution to film sound: the multi-channel analog optical soundtrack for 35 mm prints. Dolby prints have two soundtracks matrix-encoded with four sound channels: left, center, and right for speakers behind the screen, and a fourth surround channel for ambient sound and special effects heard over speakers to the sides and rear of the cinema. Other improvements include the use of Dolby A-type noise reduction to lower the hissing and popping associated with optical soundtracks, and loudspeaker equalization to adjust the cinema sound system to a standard response curve.

Dolby SR, the advanced recording process introduced in 1986, was first applied to Dolby stereo optical soundtracks (in lieu of A-type NR) the following year. Analog SR soundtracks feature a significantly improved dynamic range, and are found today on almost all 35 mm release prints. The SR track makes it possible for the prints to play in any cinema, even if it is not equipped for digital playback, and also provides a backup in case of problems with the digital track.

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Dolby Digital, introduced in 1992, takes its name from Dolby Digital (AC-3) audio coding. It features a digital optical soundtrack located between the sprocket holes on one side of 35 mm release prints. A Dolby SR analog track is also provided to ensure compatibility.

Dolby Digital provides five full-range channels for left, center, and right screen channels, plus independent left and right surround channels. A sixth channel, sometimes called the ".1" channel because it covers only the lowest one-tenth of the audible range, carries low-frequency effects that are reproduced by subwoofers.

Dolby Digital Surround EX adds a third surround channel to the Dolby Digital format. The third channel is reproduced by rear-wall surround speakers, while the left and right surround channels are reproduced by speakers on the side walls. Among the benefits are more realistic flyover and flyaround effects and a more consistent surround field throughout the auditorium.

Overview of Dolby Technologies

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5. Consumer Surround Sound

Dolby Surround is the consumer version of the original analog Dolby multichannel film sound format. When a Dolby Surround soundtrack is produced, four channels of audio information—left, center, right, and surround—are matrix-encoded onto two audio tracks. These two tracks are then carried on stereo program sources such as videotapes and TV broadcasts into the home, where they can be decoded to recreate the original four channels and the surround sound experience. Thousands of feature films on home video, as well as many television shows, are encoded in Dolby Surround.

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Dolby Surround Pro Logic is the technology that decodes program material encoded in Dolby Surround; it is built into virtually every home theater audio system. Like the professional decoder units used in cinemas, Dolby Surround Pro Logic reconstructs the original four channels—left, center, right, and surround—that were encoded onto the program material's stereo soundtracks.

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Home theater system with four-channel Dolby Pro Logic playback.

Dolby Surround Pro Logic II is an improved matrix decoding technology that provides better spatiality and directionality on Dolby Surround program material; provides a convincing three-dimensional soundfield on conventional stereo music recordings; and is ideally suited to bring the surround experience to automotive sound. While conventional surround programming is fully compatible with Dolby Surround Pro Logic II decoders, soundtracks will be able to be encoded specifically to take full advantage of Pro Logic II playback, including separate left and right surround channels. (Such material is also compatible with conventional Pro Logic decoders.)

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Dolby Digital identifies the use of Dolby Digital (AC-3) audio coding for such consumer formats as DVD and DTV. As with film sound, Dolby Digital can provide up to five full-range channels for left, center, and right screen channels, independent left and right surround channels, and a sixth ( ".1") channel for low-frequency effects.

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Home theater system with four-channel Dolby Pro Logic playback.

Dolby Headphone is a unique signal processing system that enables conventional stereo headphones to convincingly portray the sound of a multispeaker surround sound system in actual listening rooms. It can be incorporated into virtually any type of audio or video product that features a headphone output, and is also used by airlines to heighten their passengers' inflight entertainment experience.   more on Dolby Headphone technology

Dolby® Virtual Speaker technology enables true-to-life 5.1 surround sound from both multichannel and stereo programs over as few as two speakers, allowing multichannel programs to be heard as their producers intended. Its uniquely powerful, next-generation signal processing convincingly portrays the sound of properly placed surround speakers, making it ideal for use in PCs, DVD players, and TV sets. As a result, all viewing, listening, and gaming activities are transformed into realistic surround-sound experiences without the added expense and complexity of a traditional surround system.   more on Dolby Virtual Speaker

Virtual Dolby Surround and Virtual Dolby Digital technologies enable a pleasing surround-sound effect over just two speakers in a TV set or other stereo playback system. Efficient virtualizing circuitry processes the surround channels derived by the Dolby multichannel decoder, then mixes them back into the Left and Right channels. The result over two speakers is bigger, more spacious, and more involving sound than regular stereo playback provides.

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