Dolby Air conditioning 3 Sound Encoding and THX.

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The subwoofer channel is NOT the same as the LFE channel. LFE channel is made by the ... The subwoofer channel is created by the decoder at playback time ...
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Dolby AC-3 Audio Encoding & THX Wai Kam (Winnie) Henele Adams Peter Boettcher

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Multichannel Audio utilized as a part of film and different stimulation ranges from mono to stereo to 5.1 framework Wideband Audio: 48 KHz *16 bits * 6 Channels= 46.08 Mbits/sec

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AC-3: Digital Audio Coding Flexible Multi-channel coding: encode up to 6 channels and downmix as indicated by the audience\'s accessible assets Current Standard for HDTV sound pressure; additionally utilized as a part of LD, DVD Sample rates: 32 KHz, 44.1KHz, 48KHz Data rates: 32 Kbps to 640 Kbps first AC-3 coded film: Star Trek VI in Dec. 91

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AC-3 Encoder Frequency Domain Transform: 512 point MDCT with half cover 2 x 256 point MDCT in transient sign Bit allotment in gliding point representation: Mantissa and Exponent are spoken to contrastingly Bits of Mantissa are adaptively distributed

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AC-3 Decoder first Step Recover Mantissa as per Psychoacoustic model, reverse change and de-mux to various yield channels Recover PCM values for every channel second Step

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Bit-stream Syntax 1 Frame speaks to 1536 PCM tests for all channels Frame Structure SI=Sync. Information BSI=Bitstream Info CRC for blunder remedy Aux Data for private control 1 Block speaks to 256 PCM for every channel Block Structure

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Encoding Philosophy Encoding Goals Minimize saw sound quality corruption Keep the bit-rate inside set worth Bit portion methodologies forward-versatile in reverse versatile parametric piece distribution

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Forward Adaptive

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Backward Adaptive

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Parametric Bit Allocation Hybrid of Forward and Backward procedures

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Parametric Bit Allocation Core is Backward Adaptive Primary Modifications Psychoacoustic model parameter change Delta Bit Allocation

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Filter Banks Filter Bank development Overlapping squares of 512 windowed tests Block 10.66 msec long (@48kHz) Adjustments for homeless people

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Spectral Envelope Coefficients coded into an example and a mantissa Allows wide element range Precision confinements in mantissa present clamor Exponents portray the range Spectral envelope

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Spectral Envelope Coding DC sent as supreme Exponents sent as differentials Groups of 3 encoded into 7 bit pieces Four type encoding techniques D15, D25, D45, and REUSE

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Spectral Envelope

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Bit Allocation Psychoacoustic Reductions Pool of bits for all channels Adjustments made to SNR Coping with Bit rate Conditions coupling

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5.1 Channel Surround Sound 5 principle channels - L, C, R, LS, RS 1 LFE (low-recurrence impacts) channel transfer speed is roughly 1 tenth, along these lines .1 Unlike simple Dolby Surround, AC-3 5.1 organization incorporates 6 discrete channels, yet coded together for productivity

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Recommended Setup Left and Right stereo pair 45-60 degrees off kilter Surround speakers to side and somewhat to raise (110 degrees) All speakers equidistant from audience, or use proper time delays in framework. Subwoofer anyplace

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Bass Management The subwoofer channel is NOT the same as the LFE channel LFE channel is made by the sound architect at blending time The subwoofer channel is delivered by the decoder at playback time Dolby suggests alert in making LFE channels by any means

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Use of the Channels Front channels: Phantom focus (like stereo), focus channel alone, or both Surround channels: Enhance profundity and inundation Not entrenched LFE: Only uncommon bass impacts

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Decoder Downmixing

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Decoder Downmixing Decoder changes playback for hardware 5.1 sound track can be blended down to 4 channel encompass or stereo Dynamic extent decrease, LFE channel disposal

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THX Two needs recognized: A need to amend the capable of being heard tonal and spatial blunders created by the playback of soundtracks composed in and for vast theaters in the littler environment of a home. A need to all the more precisely repeat the complex and contending sound fields present in multi-channel sound playback. Also, George Lucas needs to profit

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THX Certification "THX resemble the Good Housekeeping Seal of Approval. It ensures that the item performs to a thoroughly elevated requirement that bodes well. THX gives the certainty and consolation a customer needs in a buying choice." - - Steve Baker, V.P. Deals & Marketing, Denon Electronics

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Questions What are the essential contrasts between MPEG sound and AC-3 coding? MPEG sound uses the forward versatile piece portion plan while the AC-3 strategy utilizes the cross breed (parametric) plan examined prior. The bitstream configurations are distinctive and permit diverse expansions and capacities.

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