Audio compression

Audio Compression

Prepared By: Miled OTHMEN

[email protected]

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 Conclusion2

Introduction

What is audio

• Audio is the sound system that comes with or can be added toa computer.

• An audio file is a record of captured sound that can be playedback.

• An audio card contains a special built-in processor andmemory for processing audio files and sending themto speakers in the computer.

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Introduction

What is audio

• Sound is a sequence of naturally analog signals that areconverted to digital signals by the audio card, using amicrochip called an analog-to-digital converter (ADC).

• When sound is played, the digital signals are sent to thespeakers where they are converted back to analog signals thatgenerate varied sound.

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Introduction

Some audio formats

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Introduction

What do compression mean ?

• Compression is the reduction in size of data in order to savespace 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 analgorithm to determine how to compress or decompress data.

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Introduction

Importance of compression

1 pétabyte=1000 terabyte=1000000 gigabyte

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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 wantto play it (for example with WinRAR).

If the file is compressed 'too much' there will be loss ofquality.

The compression is done with a thing called a codec.This is an aggregation of the words: compressor anddecompressor.

This codec is a special algorithm to reduce the size.

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Audio compression

Application for audio compression

• xACT (X Audio Compression Toolkit)

• XLD (X Lossless Decoder): is able to decode/convert/playvarious 'lossless' audio files.

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Audio compression

Application for audio compression

• Monkey’s audio: is a fast and easy way to compress digitalmusic.

• Free Audio Editor

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Audio compression

Diagram for audio compression

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Audio compression

Diagram for audio decompression

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Types of compression

Lossy compression

• A compression technique that does not decompress data backto 100% of the original.

• Lossy methods provide high degrees of compression andresult in smaller compressed files, but there is a certainamount of visual loss when restored.

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Types of compression

Lossy compression

• Audio can tolerate loss, and in many cases, it may not benoticeable to the human ear.

• In other cases, it may be noticeable, but not that critical tothe application.

• The more tolerance for loss, the smaller the file can becompressed, and the faster the file can be transmitted over anetwork.

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Types of compression

Lossy compression

Example of lossy file format:

MP3

• The MP3 format’s history is legendary when it comes to digitalmusic and the Internet.

• It has single handedly revolutionized the way we listen to and sharemusic.

• Even its name has become part of our everyday language, MP3music and MP3 players are terms that are used to describe all kindsof formats and players.

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Types of compression

Lossy compression

Example of lossy file format:

MP3

• The compression algorithm that the MP3 standard uses is a lossyone.

• The MP3 encoding process takes advantage of psychoacousticalgorithms that filter out frequencies that humans are unlikely tohear.

• Low frequencies are either filtered out or are converted to monosignals - this requires less storage space.

• The human ear can’t detect directions of low frequencies very welland so a stereo signal isn’t necessary. Another way that MP3compression can reduce file size while keeping the quality is to dropquieter sounds in preference for louder sounds, it is unlikely thatthe listener will notice any difference.

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Types of compression

Lossless compression

• A compression technique that decompresses data back to itsoriginal form without any loss.

• The decompressed file and the original are identical. Forexample, the ZIP archiving technology (WinZip...) is the mostwidely used lossless method.

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Types of compression

Lossless compression

• Lossless audio files typically require more storage space thanlossy encoded ones.

• However this type of format is often favored by users wantingto backup original audio CDs.

• a perfect copy can be restored in the event of loss or damageto the CD.

• FLAC, Apple Lossless (ALAC) and WMA Lossless are examplesof lossless compression formats.

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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.

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Standard Codecs for audio compression

For lossless compression

• LPAC (Lossless predictive audio compression):is an improvedlossless audio compression algorithm developed by TilmanLiebchen, Marcus Purat and Peter Noll.

• ALAC (Apple Lossless Audio Codec):is an audio coding format,and its reference audio codec implementation, developed byApple.

• FLAC(Free Lossless Audio Codec): can typically reduce theoriginal size of audio file to 50–60%, and decompressed it toan identical copy of the original audio data, developed by JoshCoalson.

• WMA Lossless (Windows Media Audio Lossless): developed byMicrosoft .

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Standard Codecs for audio compression

For lossy compression

• Nero AAC Codec(Nero “advanced audio coding” codec): It wasdeveloped and distributed by Nero AG.

• FAAC(Freeware Advanced Audio Coder):is an audiocompression computer program that creates AAC sound filesfrom other formats , it is the recommended format for thecompany's iPod music player.

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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

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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

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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 algorithmsmany applications• Better algorithms better quality, more compression

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