By :-

Ishank Ranjan

Akash Gupta

Audio & Audio File Formats

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.

It can be a raw bitstream, but it is usually a container format or an audio data format with defined storage layer.

Audio Format/Codec It is important to distinguish between a file format and

an audio codec.

A codec performs the encoding and decoding of the raw audio data while the data itself is stored in a file with a specific audio file format.

In other words, Codec contains both an ADC and DAC running off the same clock.

Audio

Source

Audio

Acquiring

Audio

Processing

Audio

Output

Audio

Encoding

3 Categories of Audio FilesThere are 3 categories in which certain Audio files belong to:-

Uncompressed: Audio files that are not compressed and are capable of having a large file size. Ex) .Wav

Lossless: Audio files that are compressed but doesn’t lose any quality to the file. Ex) .WMA

Lossy: Audio files that lose some quality when being compressed. Ex) .Mp3

Uncompressed Audio Formats There is one major uncompressed audio format, PCM,

which is usually stored in a .wav file on Windows or in a .aiff file on Mac OS.

Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals.

BWF (Broadcast Wave Format) is a standard audio format created by the E.B.U.as a successor to WAV.

BWF allows metadata to be stored in the file

Features of Uncompressed file Formats WAV and AIFF are flexible file formats designed to

store more or less any combination of sampling rates or bitrates.

This makes them suitable file formats for storing and archiving an original recording.

Examples….

WAV(.wav)

AIFF(.aiff, .aif, .aifc)

AU(.au,.snd)

raw header-less PCM

Lossless Audio Formats A lossless compressed format stores data in less space

by eliminating unnecessary data.

Uncompressed audio formats encode both sound and silence with the same number of bits per unit of time.

In a lossless compressed format, the music would occupy a smaller portion of the file and the silence would take up almost no space at all.

Features OfLossless Compressed Audio Format Lossless compression formats enable the original

uncompressed data to be recreated exactly.

They provide a compression ratio of about 2:1.

Examples… FLAC(.flac)

WavPack(.wv)

Monkey's Audio(.ape)

ALAC (Apple Lossless)(.m4a)

Lossy Audio Formats

Lossy compression enables even greater reductions in file size by removing some of the data.

Lossy compression typically achieves far greater compression but somewhat reduced quality than lossless compression by simplifying the complexities of the data.

A variety of techniques are used, mainly by exploiting psychoacoustics, to remove data with minimal reduction in the quality of reproduction

Features ofLossy Compressed Audio Formats Most formats offer a range of degrees of compression,

generally measured in bit rate.

The lower the rate, the smaller the file and the more significant the quality loss.

Examples…

MP3,

Vorbis (.ogg ,.oga)

Musepack (.mpc, .mp+, .mpp)

AAC(.m4a, .m4b, .m4p, .m4v, .m4r, .3gp, .mp4, .aac)

ATRAC (.aa3,.oma,.at3)

Windows Media Audio Lossy (WMA lossy)(.wma)

Most common audio files The most common types of

audio files that are still being used today are .Wav files and .Mp3 files. Mp3 files are the most popular because it’s used for downloading and storing music into your computer, CD player, or mp3 player. Wave files are used for storing CD-quality sound files, which can be large in size.

WAVE

WAVE means storing a pattern of music signals in digital wave form on computer.

This means that any sound can be stored.

However, these sound files are huge and process over 160KB per second.

These files can be seen with a suffix of .wav (e.g. Fred.wav)

MP3 MP3, or MPEG level 3 indicates a type of sound file

found on computers.

MP3 is designed to store music at CD quality but using approximately 1/12th of the space.

This compression method is PERCEPTIVE ENCODING. This means that approximately 90% of the music which the human ear does not respond to (I.e. duplicate notes, quieter sounds etc.) is removed.

MIDI MIDI stands for Musical Instrument

Digital Interface and is used with computers.

Where a CD stores sound music, MIDI is the manuscript version. It also involves hardware within the computer (including cables, keyboard, computer sequencers, synthesisers, instruments etc)

It stores the pitch, volume and which instrument is being played.(channel)

MIDI comes from the notation side of music and is best thought of in terms of an orchestral score where lots of different instruments can be put together in one entity.

THANK YOU