Multichannel cinema sound

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Multichannel cinema sound
A presentation in SMD074 Jens Eliasson Ulrika
Leijon Emil Persson
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Why multi-channel audio?

• We only have two ears, isn?t stereo enough then?
• Can we emulate multiple sound sources with stereo?

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Why multi-channel audio?

• Multi-channel emulation works quite well
• Doesn?t beat the real thing though.

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Common multi-channel configuration

• Quadraphonic
• Front left right rear left right
• 5.1
• Front left right rear left right center
  LFE (Low Frequency Effects)

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Applications of multi-channel audio

• Music
• Improved music listening experience.
• Movies
• Can enhance the experience a lot.
• Computer games
• Improves the feeling of being in the game.
• May improve your fragrate.
• Need special hardware and additional game
  programming efforts.

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Sources that deliver 5.1 sound

• A DVD with a 5.1-channel Dolby AC-3 soundtrack
• A DTS-encoded DVD or CD
• A satellite TV-channel (HDTV)
• A DVD-Audio disc

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What is 5.1 ?
Center
LFE
Left front
Right front
Left surround
Right surround
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The development of surround sound
Disney's Fantasia
The world's first video recorder
Quadraphonic
1992
1982
1956
1930
1950
1990
1970
1940
1960
2000
1980
1931
1987
1993
1977
Stereo patent
Cinerama movies
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DD vs. DTS

• Which is the best?
• No general answer.
• Both have advantages and disadvantages.

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DD vs. DTS

• DD is a perceptual codec.
• Lossy.
• Low bandwidth needs.
• DTS is perceptual and lossless combined.
• Lossy and lossless available.
• Higher bandwidth needs, often 3 times DD.
• Studio quality.

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DD vs. DTS

• DD
• Only up to 48 KHz sampling rate.
• May need lowpass filter before encoding.
• Enough for humans ears.
• DTS
• Up to 192 KHz and possibly beyond.
• Considered studio quality.

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DD vs. DTS

• DD
• Industry standard.
• Mandatory on DVDs.
• DTS
• Later arrival in the match.
• Thus, DTS tracks are optional on DVDs.

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DD vs. DTS

• DD - More fixed design
• Changes to spec. may require new hardware.
• Don?t waste any bits and bytes.
• DTS - Flexible design
• Decoding instruction along with audio data.
• ?Future proof?
• Simplier and potentially cheaper decoding
  hardware.

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Why use a codec?

• Easier to work with - all six channels works an
  one entity.
• Enables down mix from 5.1 to Dolby Surround.
• Much lower bit-rate due to compression
• CD 1500 Kbps
• 5.1 in CD quality 9000 Kbps
• Dolby Digital 5.1 (AC-3) 380-640 Kbps
• DTS 1400-1500 Kbp

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Dolby AC-3

• Developed in 1991
• A compression ratio of 101, a dynamic range
  120db, a frequency response of 20-20,000Hz, and
  a 16-bit data rate of 384 Kbps