here we are discribe audio compression technique.

1. Prepared By:Avni Guna.
Khushali Panasala.
Yogesh Pandey.
Priyanka Pandey.
Hiteshri Patel.
Guided By:Mr.Chandresh
Parekh.

2.  Introduction
 What Is Audio?
 Why Compression is needed?
 Audio Compression.
 Types Of Audio Compression.
 Standard codecs for audio compression.
 Categories of Audio Files
 MPEG Audio Encoding Steps
 MPEG Audio decoding
 Successor of MP3

3.  High quality audio coding based on perceptual models has
found its way to widespread application in broadcasting and
Internet audio (e.g. mp3).
 Algorithms defined by the MPEG group (MPEG-1 Audio, e.g.
MPEG Layer-3 (mp3), MPEG-2 Advanced Audio Coding,
MPEG-4 Audio including its different functionalities) still
define the state of the art.

4.  Audio is an electrical or other
representation of sound.
 An audio file format is a file
format for storing digital audio
data on a computer system.

5. • 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. • 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.  There are mainly two types of audio compression show
below:
1)Lossy Compression(MP3)
2)Lossless Compression(Winzip)

9. • 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.
• Example:MP3

10. • 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.

11. • 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.

12.  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.

13.  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

14.  Moving Picture Experts Group
 Aim to create standards relating to synchronized
 audio and video compression
 MPEG-1
 MPEG-2

15. Quite good
high bit-rate is
available
Digital audio tap
Complex
Digital Audio
Broadcasting
most complex
audio transmission
over ISDN lines

16. There are 3 categories in which certain Audio files
belong to:-
1) Uncompressed:
Ex) .Wav
2) Lossless:
Ex) .WMA
3) Lossy:
Ex) .Mp3

24. ◦ Hearing threshold level – a function of frequency
◦ Any frequency components below the threshold will
not be perceived by human ear

25.  A frequency component can be partly or fully masked by
another component that is close to it in frequency
 A lower tone can effectively mask higher tone
 This shifts the hearing threshold

26. ◦ A quieter sound can be masked by a louder
sound if they are temporally close Sounds that
occur both (shortly) before and after volume
increase can be masked

28.  Power-law: larger values have less accuracy
 quantization: uniform or non-uniform quantization.
 coding: quantized spectral components are transmitted
either directly, or as entropy coded words (Huffman
coding)
 For better data compression, variable- length Huffman
codes are used to encode the quantized samples.
 Resultant bitstream is now reduced, because of coarser
quantisation, but can be further reduced by the use of
Huffman coding.

29.  formats encoded quantized samples into an
encoded bit stream – final form in which the
compressed signal is transmitted.
 Header (First 4 bytes of a frame)
◦ Contains: Frame Sync, MPEG Layer, Sampling Frequency,
Number of Channels, CRC, etc.
◦ Variable bit rate mp3’s switch bitrate between frames

30.  Decoder side relatively easier. The gain, scale
factor, quantization steps recovered and used for
reconstruct the filter bank responses
 Filter bank responses are combined to reconstruct
the decoded audio signal

31.  Advanced Audio Coding (AAC) – now part of MPEG-
4 Audio
 Inclusion of 48 full-bandwidth audio channels
 Default audio format for iPhone, iPad, Nintendo,
PlayStation, Nokia, Android, BlackBerry
 Introduced 1997 as MPEG-2 Part 7
 In 1999 – updated and included in MPEG-4
 standard for lossy digital audio compression. Designed
to be the successor of the MP3 format, AAC generally
achieves better sound quality than MP3 at similar bit
rates.

32.  Opus is a lossy audio coding format developed by the
Internet Engineering Task Force (IETF) that is
particularly suitable for interactive real-time
applications over the Internet.
 Opus incorporates technology from two other audio
coding formats: the speech-oriented SILK and the low
latency CELT.

33.  The MDCT was proposed by Princen, Johnson, and
Bradley[1] in 1987, following earlier (1986) work by
Princen and Bradley[2] to develop the MDCT’s
underlying principle of time-domain aliasing
cancellation (TDAC), described below.
 In MP3, the MDCT is not applied to the audio signal
directly, but rather to the output of a 32-band polyphase
quadrature filter (PQF) bank. The output of this MDCT
is post processed by an alias reduction formula to
reduce the typical aliasing of the PQF filter bank.

34.  Such a combination of a filter bank with an MDCT is
called a hybrid filter bank or a sub band MDCT. AAC,
on the other hand, normally uses a pure MDCT; only
the (rarely used) MPEG-4 AAC-SSR variant (by Sony)
uses a four band PQF bank followed by an MDCT.
Similar to MP3, ATRAC uses stacked quadrature
mirror filters (QMF) followed by an MDCT.

35.  ISO/IEC
• MPEG-1 Layer III (MP3)
• MPEG-1 Layer II
• MPEG-1 Layer I
• AAC
• MPEG-4 ALS
• MPEG-4 SLS
• MPEG-D USAC

36.  ITU-T
• G.711
• G.718
• G.719
• G.722
• G.723
• G.726
• G.728
• G.729

37. • audio compression is a key technology
• many algorithms  many applications
• Better algorithms  better quality, more compression

38. Thank You