DOLBY SOUND PROCESSINGSeminar by:

BRIEF HISTORY OF DOLBY LABS

Founded by Ray Dolby in Britain in 1965. The first product he made was Type A Dolby

Noise Reduction, a simple compander. Dolby marketed the product to record

companies. The first film with Dolby sound was A

Clockwork Orange (1971), which used Dolby noise reduction.

TIMELINE OF IMPORTANT DOLBY INNOVATIONS

In 1984, Dolby releases Dolby AC-1, their first digital coding system.

In 1987, Dolby Pro Logic surround technology elevates the home cinema experience with four-channel surround sound.

In 2002, Dolby Virtual Speaker technology introduced.

First public demonstration of 5.1-channel surround sound on a mobile phone using Dolby Mobile technology in 2010.

TECHNOLOGIES

Analog audio noise reduction Dolby A/B/C/S-Type NR, Dolby SR (Spectral

Recording), Dolby FM, Dolby HX Pro. Audio encoding/compression

Dolby Digital (also known as AC-3), Dolby E, Dolby Stereo, Dolby TrueHD, AAC, aacPlus, Dolby Pulse.

Audio processing Dolby Headphone, Dolby Virtual Speaker, Dolby

Surround, Dolby Pro Logic, Dolby Pro Logic II, Dolby Pro Logic IIx, and Dolby Pro Logic IIz

Video processing Digital Cinema Live Sound

TECHNICAL DETAILS

The data layout of AC-3 is described by simplified "C-like" language in official specifications.

An AC-3 stream is a series of frames; each with a fixed number of 6 audio blocks; each audio block contains 256 audio samples per channel. For example, a 5.1 AC-3 bitstream contains 1536

samples per audio block (6 channels × 256 samples/channel).

Channel blocks can be either long, in which case the entire block is processed as single modified discrete cosine transform or short, in which case two half length transforms are performed on the block.

TECHNICAL DETAILS(CONTD.)Field Name # of bits Description

syncword 160x0B77   Transmission of data is left bit first (big

endian).CRC 16

Sampling frequency 2'11'=reserved '10'=32 kHz

'01'=44.1 '00'=48

Frame Size Code 6

Bit Stream Identification 5

Bit Stream Mode 3 '000'=main audio service

Audio Coding Mode 3'010'=left, right channel

orderingCenter Mix level 2

Surround Mix Level 2

Dolby Surround Mode 2'00'=not indicated '01'=Not surround encoded '10'=Yes,

surround encoded.

DOLBY DIGITAL

Audio compression technologies developed by Dolby Laboratories.

It was originally called Dolby Stereo Digital until 1994.

Except for Dolby TrueHD, the audio compression is “lossy”.

It is now also used for other applications such as TV broadcast, DVDs, Blu-ray discs and game consoles.

STEREO/SURROUND PROCESSING

1. Stereo Enhancement2. Surround Enhancement3. Dolby Pro-Logic

STEREO ENHANCEMENT

Objective Expand the Sound Fields beyond the two

speakers Imitate Surround Sound Effects Flexible with Environments and Audio Contents

Consideration Dialog Localization ( below 4 kHz) Sweet Spots (1 -2kHz)

General FormL?= L + K1(L+R)) + K2(L-R)R?= R + K1(L+R)) -K2(L-R)

K is function of frequency, speaker distance, audio contents, and the degree of coherent of left-and right channels.

STEREO ENHANCEMENT (CONTD.)

Spatializer Technique Lout = L +CL Rout= R –CR HP: cut-off at 300, Slope 18dB/Oct. L-Eq.: Resonant at 1.5 kHz. R-Eq.: Resonant at 3kHzp

SRS Technique Lout = L + K1(L+R)p+ K2(L-R) p

Rout= R + K1(L+R)p-K2(L-R) p

(L+ R)p: Processed sum signal. (L-R)p: Processed difference signal.

SURROUND PROCESSING

Synthesizes the additional sound channels to expand the output from the conventional two channels to four or five.

There are specific objectives regarding the performance of home surround system, such as good dialog intelligibility, precise localization of specific sound events, natural ambience, etc. In order to fulfill the objectives, additional

information on the center dialog channel and surround channel is encoded into the two channel stereo signals and then decoded to result in four distinct output channels in the surround processor system like Dolby Surround.

SURROUND PROCESSING (CONTD.)

The three major components of the film sounds Dialog:

most important is desired to be directed to center loudspeaker and to

be removed from left and right loudspeakers for the coincidence of visual screen and audio sound

Music mixed into the sound track come from front with some auditory event width

Effect sound originate from any direction

DOLBY PRO-LOGIC

What is Dolby Prologic? A process for encoding and decoding four

independent channels of audio data into two channels for storage and transmission. It is designed to improve localization by actively steering dominant audio information to its proper spatial location,

Dolby Pro-Logic is developed from surround sound reproduction technique for movie theaters.

DOLBY PRO-LOGIC (CONTD.)

Active Surround Encoder Center channel is encoded as the sum of left and

right channel. Surround channel data is encoded as a difference

between the left and right channel (L-R, band limited to 7 KHz and encoded with B-type noise reduction as well as delayed several milliseconds)

DOLBY PRO-LOGIC (CONTD.)

DOLBY ENCODING MATRICESDolby Surround Left Right Surround

Left Total 1 0

Right Total 0 1

Dolby Pro Logic Left Right Center Rear

Left Total 1 0

Right Total 0 1

Dolby Pro Logic II

Left Right Center Rear Left Rear Right

Left Total 1 0

Right Total 0 1

APPLICATIONS Dolby Digital audio is used on DVD-Video and other

purely digital media, like home cinema. In this format, the AC-3 bitstream is interleaved with the video and control bitstreams.

The system is used in bandwidth-limited applications other than DVD-Video, such as digital TV.

Dolby is part of a group of organizations involved in the development of AAC (Advanced Audio Coding), part of MPEG specifications, and considered the successor to MP3. AAC outperforms MP3 at any bitrate, but is more complex.

Dolby Digital Plus (DD-Plus) and TrueHD are supported in HD DVD, as mandatory codecs, and in Blu-ray Disc, as optional codecs.

HAVE A HAPPY MOVIE WATCHING EXPERIENCE WITH DOLBY…………………….!!!!!!!