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By: T’quoia Boyd Science 2005

How do MP3's Work?. By: T’quoia Boyd Science 2005. Glossary. Encoder- a part in MP3 that turns messages into codes Polyphase filter bank-a part used in MP3 to separate sound signals MDCT-a part used with Polyphase filter bank for song compression. Glossary,continued.

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By: T’quoia Boyd Science 2005

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  1. How do MP3's Work? By: T’quoia Boyd Science 2005

  2. Glossary • Encoder- a part in MP3 that turns messages into codes • Polyphase filter bank-a part used in MP3 to separate sound signals • MDCT-a part used with Polyphase filter bank for song compression

  3. Glossary,continued • Implementation- another word for placement • Bit rate-number of bits moved per unit of time • Iteration-repeating a process to improve accuracy of a result • Hybrid Filter bank- simply the MDCT and Polyphase filter bank together

  4. Glossary,continued • Quantization- sampling analog waves and changing them into digital data • Analog wave-continuous electrical [sound] waves that represent a number of values (carry sound through speakers)

  5. History • 1987-Institute worked on perceptual coding • 1992-MPEG-1 • 1997-student created AMP MP3 playback engine • 1998-WinAmp is free MP3 music player

  6. Details • Filter bank • Perceptual model • Joint stereo • Quantization & coding • Iteration loops • Surround extension

  7. 1. Filter Bank • Filter bank in Layer-3 is called a hybrid filter bank • Chose for compatibility with Layer-1 and Layer-2 • Filter bank consist of a polyphase filter ban and a Modified Discrete Cosine Transform (MDCT)

  8. 2.Perceptual Model • Perceptual model determines quality of given encoder implementation • Uses either a separate filter bank or provided calculations

  9. 3. Joint Stereo • used where low bitrates are available but stereo signals are desired

  10. 4. Quantization and Coding • 2 nested iteration loops- common solution in Layer-3 • Quantified values coded by Huffman coding • Noiseless coding-no noise added to audio signal

  11. 5. Iteration Loops • Outer iteration loop-noise control/distortion loop • Inner iteration loop-rate loop • Rate loop is nested within noise control loop

  12. 6.Surround Extension • Introduced in 2004 • based on cue coding approach

  13. Example of Compression • “Ask not what your country can do for you-- ask what you can do for your country” • 1.ask 2.what. 3.your 4.country 5.can 6.do 7.for 8.you • 1 not 2345678--12856734

  14. Compression • MP3 compresses file so it takes shorter time to download • computer software expands file to regular size • sends file to sound card • turns into analog wave for speakers

  15. About the Author • My name is T’quoia Boyd. My birthday is on July 20, 1992. I like babysitting, drawing, Pepsi,cocoa, and Tigger.

  16. The iPod The iPod is the coolest new MP3 player amongst us teens. Available in stores now!! Also try the new iPod Shuffle. The new small version of your favorite MP3 player!!

  17. Bibliography • About MP3s. 26 Oct.Winamp.26 April.2005.<http://www.howstuffworks.com/mp3/> • Layer-3 Basics.2 June.2003.Turner Television Network.26 April.2005.<http://ftp.rge.com/pub/multimedia/mpeg-al3/13fag.html>

  18. Bibliography,continued • MPEG Audio Layer-3. 17 Dec.2003.Purdue University.2 May.2005.<http://www.ii.fraunhofer.de/amm/technf/Layer3/> • Neudfeldt,Victoria ed.Webster’s New World School and Office Dictionary.New York, NY:Simon & Schuster,Inc..,1995

  19. THE END

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