By: T’quoia BoydBy: T’quoia BoydScience 2005Science 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• 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

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)

History• 1987-Institute worked on perceptual coding

• 1992-MPEG-1• 1997-student

created AMP MP3 playback engine

• 1998-WinAmp is free MP3 music player

Details

• Filter bank• Perceptual model• Joint stereo• Quantization &

coding• Iteration loops• Surround

extension

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)

2.Perceptual Model• Perceptual model determines

quality of given encoder implementation

• Uses either a separate filter bank or provided calculations

3. Joint Stereo• used where low bitrates are

available but stereo signals are desired

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

5. Iteration Loops• Outer iteration loop-noise

control/distortion loop• Inner iteration loop-rate loop• Rate loop is nested within noise

control loop

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

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

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

About the Author• My name is

T’quoia Boyd. My birthday is on July 20, 1992. I like babysitting, drawing, Pepsi,cocoa, and Tigger.

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!!

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>

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

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