MP3 and DVD Audio

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MP3 and DVD Audio
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What is MP3?

• MPEG-1, Layer III
• Developed in later 80s and early 90s and
  finalised in November 1992 by MPEG as MPEG-1
  standard
• MP3 is more than a simple compression scheme
• Simple compression (eg. Zip) for WAV file doesnt
  compress well in raw audio Only shave tiny
  percentage from the original file size

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• MP3 gets most of its compression from the science
  of psychoacoustic.
• Uncompressed audio streams carry a lot of data
  that isnt actually perceived by humans
• MP3 encoders analyse audio streams and compare
  them to mathematical models of human
  psychoacoustics.
• This compression is far more complicated to zip
  but achieved more effective file size

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MP3 technical details

• Raw audio is encoded as much useful information
  as possible given the restrictions set by the bit
  rate and sampling frequency.
• There are number of step comprise the encoding
  process
• Audition threshold
• Masking effects
• Reservoir of bytes
• Joint stereo
• Huffman encoding

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Audition Threshold

• Most streams cover a frequency range much broader
  than that which humans can hear
• Human hearing range generally falls between 20Hz
  and 20kHz with mist sensitive between 2khz to
  4khz.
• MP3 encoders discard frequencies above and below
  this range

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Masking Effects

• Two or more sounds are played simultaneously and
  one sound is louder than the other, the louder
  sound hides (masks) the softer one.
• The softer sound still present in the recorded
  spectrum
• Therefore, MP3 will remove the softer sound from
  the spectrum as they appear imperceptible
• The file size will drop dramatically in this
  process

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Reservoir of bytes

• Like movie, MP3 files are stored in a series of
  frames
• Each frame carries a fraction of a second audio
  data and preceded by a header section describing
  the bitrate, encoding method and other metadata
  pertaining to the frame to come
• In some cases, a portion of the audio stream may
  be adequately encoded with room leftover in its
  frame.
• The reservoir of bytes let the MP3 encoder borrow
  space from unfilled frames to store data of
  adjacent frames that need additional space
• Space lending concept that helps to endure a
  consistent flow of data and quality rate

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Joint stereo

• Optional feature in MP3 encoding
• When this feature is enable, the stereo sound is
  represented using a mixture of true stereo and
  mono sound.
• MP3 can encode very low and very high frequency
  in mono thereby space saving

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Huffman encoding

• MP3 encoding process employ the classic Huffman
  encoding algorithm. After all psychoacoustic
  methods have been applied, the Huffman encoding
  compresses any remaining redundancies in the bit
  pattern
• It is great encoding at handling redundancies,
  for example a text file filled with a millions
  zeros will compress to almost nothing
• On average this technique allows a saving of 20
  in file size

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Encoding MP3

• Two ..
• 64Kbps and below voice, lectures, streaming over
  modem
• 96Kbps low-fi music or hi-fi voice
• 128Kps music files for internet distribution
• 160Kps or 192Kps Music file for personal
  collection
• 256Kps or 360Kps Files for more demanding
  audiophiles virtually perfect quality but large
  size
• All bitrate use CD-quality 44.1kHz sample rate
• 64Kps or below are recommend to use lesser rates
  of 22kHz or 11KHz to achieve adequate compression
  for lower bitrates

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DVD audio

• DVD audio specification included many of the same
  capabilities as DVD video
• DVD audio provide super-high-fidelity audio and
  music album orientated interactive capabilities
• Compression technique applied Meridian Lossless
  Packing (MLP)

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MLP

• Difference between MLP and lossy compression used
  in MPEG is that MLP does not discard any audio
  information.
• MLP on average reduces the size of the file by
  about 50
• A DVD audio disc can deliver a single channel up
  to 192 kHz or up to six channels of 96kHz, 24 bit
  surround sound.
• DVD audio allows a higher data rate for audio
  tracks 9.6Mbps compared to 6.144Mbps limit in
  DVD video
• DVD audio supports PCM audio, Dolby Digital AC-3
  and MPEG audio

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DVD Audio features

• Still images
• Text
• Video
• Menu and navigation
• Playlist
• Lyrics and linked lyrics
• Music markers