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Audio compression

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présentation with powerpoint 2013 about audio compression

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Audio compression

  1. 1. Audio Compression Prepared By: Miled OTHMEN Miled.othman@gmail.com
  2. 2. Agenda 1 Introduction 2 Audio compression 3 Types of compression 4 Standards Codecs for audio compression 5 International organizations dealing with audio compression standardization 6 Conclusion 2
  3. 3. Introduction What is audio • Audio is the sound system that comes with or can be added to a computer. • An audio file is a record of captured sound that can be played back. • An audio card contains a special built-in processor and memory for processing audio files and sending them to speakers in the computer. 3
  4. 4. Introduction What is audio • Sound is a sequence of naturally analog signals that are converted to digital signals by the audio card, using a microchip called an analog-to-digital converter (ADC). • When sound is played, the digital signals are sent to the speakers where they are converted back to analog signals that generate varied sound. 4
  5. 5. Introduction Some audio formats 5
  6. 6. Introduction What do compression mean ? • Compression is the reduction in size of data in order to save space or transmission time. • Compression can be used to:  Reduce File Size  Save disk space  Reduce transmission time • Compression is performed by a program that uses an algorithm to determine how to compress or decompress data. 6
  7. 7. Introduction Importance of compression 1 pétabyte =1000 terabyte =1000000 gigabyte 7
  8. 8. Audio compression Definition • Audio compression is a form of data compression designed to reduce the size of audio files. • There is a conditions on this definition :  the audio file must still be playable after compression, without decompressing it to original size when you want to play it (for example with WinRAR).  If the file is compressed 'too much' there will be loss of quality.  The compression is done with a thing called a codec. This is an aggregation of the words: compressor and decompressor.  This codec is a special algorithm to reduce the size. 8
  9. 9. Audio compression Application for audio compression • xACT (X Audio Compression Toolkit) • XLD (X Lossless Decoder): is able to decode/convert/play various 'lossless' audio files. 9
  10. 10. Audio compression Application for audio compression • Monkey’s audio: is a fast and easy way to compress digital music. • Free Audio Editor 10
  11. 11. Audio compression Diagram for audio compression 11
  12. 12. Audio compression Diagram for audio decompression 12
  13. 13. Types of compression Lossy compression • A compression technique that does not decompress data back to 100% of the original. • Lossy methods provide high degrees of compression and result in smaller compressed files, but there is a certain amount of visual loss when restored. 13
  14. 14. Types of compression Lossy compression • Audio can tolerate loss, and in many cases, it may not be noticeable to the human ear. • In other cases, it may be noticeable, but not that critical to the application. • The more tolerance for loss, the smaller the file can be compressed, and the faster the file can be transmitted over a network. 14
  15. 15. Types of compression Lossy compression Example of lossy file format: MP3 • The MP3 format’s history is legendary when it comes to digital music and the Internet. • It has single handedly revolutionized the way we listen to and share music. • Even its name has become part of our everyday language, MP3 music and MP3 players are terms that are used to describe all kinds of formats and players. 15
  16. 16. Types of compression Lossy compression Example of lossy file format: MP3 • The compression algorithm that the MP3 standard uses is a lossy one. • The MP3 encoding process takes advantage of psychoacoustic algorithms that filter out frequencies that humans are unlikely to hear. • Low frequencies are either filtered out or are converted to mono signals - this requires less storage space. • The human ear can’t detect directions of low frequencies very well and so a stereo signal isn’t necessary. Another way that MP3 compression can reduce file size while keeping the quality is to drop quieter sounds in preference for louder sounds, it is unlikely that the listener will notice any difference. 16
  17. 17. Types of compression Lossless compression • A compression technique that decompresses data back to its original form without any loss. • The decompressed file and the original are identical. For example, the ZIP archiving technology (WinZip...) is the most widely used lossless method. 17
  18. 18. Types of compression Lossless compression • Lossless audio files typically require more storage space than lossy encoded ones. • However this type of format is often favored by users wanting to backup original audio CDs. • a perfect copy can be restored in the event of loss or damage to the CD. • FLAC, Apple Lossless (ALAC) and WMA Lossless are examples of lossless compression formats. 18
  19. 19. Types of compression The most popular type of audio compression currently used is lossy due to encoded files being smaller than lossless ones while still retaining acceptable sound quality. 19
  20. 20. Standard Codecs for audio compression For lossless compression • LPAC (Lossless predictive audio compression):is an improved lossless audio compression algorithm developed by Tilman Liebchen, Marcus Purat and Peter Noll. • ALAC (Apple Lossless Audio Codec):is an audio coding format, and its reference audio codec implementation, developed by Apple. • FLAC(Free Lossless Audio Codec): can typically reduce the original size of audio file to 50–60%, and decompressed it to an identical copy of the original audio data, developed by Josh Coalson. • WMA Lossless (Windows Media Audio Lossless): developed by Microsoft . 20
  21. 21. Standard Codecs for audio compression For lossy compression • Nero AAC Codec(Nero “advanced audio coding” codec): It was developed and distributed by Nero AG. • FAAC(Freeware Advanced Audio Coder):is an audio compression computer program that creates AAC sound files from other formats , it is the recommended format for the company's iPod music player. 21
  22. 22. International organizations dealing with audio compression standardization • MPEG-1 Layer III (MP3) • MPEG-1 Layer II • MPEG-1 Layer I • AAC • MPEG-4 ALS • MPEG-4 SLS • MPEG-D USAC • ISO/IEC 22
  23. 23. International organizations dealing with audio compression standardization • G.711 • G.718 • G.719 • G.722 • G.723 • G.726 • G.728 • G.729 • ITU-T 23
  24. 24. Conclusion The most popular type of audio compression currently used is lossy due to encoded files being smaller than lossless ones while still retaining acceptable sound quality. • audio compression is a key technology • many algorithms  many applications • Better algorithms  better quality, more compression 24
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