Project on Audio File Formats

By :-Ishank RanjanAkash Gupta

Audio & Audio File FormatsAudio 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.

AudioSource

AudioAcquiring

AudioProcessing

AudioOutput

AudioEncoding

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 FormatsThere 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 FormatsWAV 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 FormatsA 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 FormatLossless 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 FormatsLossy 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 FormatsMost 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.

WAVEWAVE 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)

MP3MP3, 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.

MIDIMIDI 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.

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