1 digital audio storage formats. 2 formats there are many different formats for storing and...

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1 Digital Audio Storage Formats

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Digital Audio Storage Formats

Digital Audio Storage Formats

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FormatsFormats

There are many different formats for storing and communicating digital audio:CD audioWavAiffAuMP3

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WAVEWAVE

Waveform Audio (wave or .wav) is a file format in which Windows stores sounds as waveforms

The WAVE format is a subset of RIFF (Resource Interchange File Format) used for storing digital audio

Basic .wav files store information in PCM format with no compression

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.wav.wav

Wave files contain 3 parts:DescriptorFormat

informationData

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Chunk DescriptorChunk Descriptor

ChunkID - Contains the letters “RIFF” in ASCII form

ChunkSize - This is the size of the entire file in bytes minus 8 bytes for the two fields not included in this count: ChunkID and ChunkSize

Format - Contains the letters “WAVE” in ASCII from

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Format Sub-chunkFormat Sub-chunk

Subchunk1ID - Contains the letters “fmt” Subchunk1Size - 16 for PCM. This is the

size of the rest of the sub-chunk which follows this number

AudioFormat - PCM = 1 (i.e. Linear quantization). Values other than 1 indicate some form of compression

ByteRate - SampleRate * NumChannels * BitsPerSample / 8

BlockAlign - NumChannels * BitsPerSample / 8 The number of bytes for one sample

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Data Sub-chunkData Sub-chunk

Subchunk2ID - Contains the letters “data”

Subchunk2Size – NumSamples * NumChannels * BitsPerSample / 8 This is the number of bytes in the data

Data - The actual PCM sound data8-bit samples are stored as unsigned bytes,

ranging from 0 to 255. 16-bit samples are stored as 2’s-complement signed integers, ranging from -32768 to 32767

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.au.au

Sun’s audio file formatFile is composed of three parts:

24-byte headervariable-length annotation blockcontiguous segment of audio data

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Header InformationHeader Information

Magic Number - 4 bytes - “.snd”hdr_size - 4 bytes - offset to start of audio

data   data_size - 4 bytes - data length, in bytes

(optional)encoding - data encoding type code sample_rate - samples per second channels - number of interleaved channels

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AIFFAIFF

Apple’s Audio Interchange File Format RIFF (and thus .wav) is derived from AIFF File is split into:

Header, Common and Data Chunk• ChunkID - Contains the letters “FORM" in ASCII.

• ChunkSize - This is the size of the entire file in bytes minus 8 bytes for the two fields not included in this count: ChunkID and ChunkSize.

• Format - Contains the letters “AIFF”Common chunk – information on data formatData chunk – PCM audio data

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MIDIMIDI

Musical Instrument Digital InterfaceSerial interface standard for interfacing between

electronic instruments (31.25Kbits uni-directional) Involves communicating sound events rather than

sampled audio

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MIDIMIDI

The information transmitted between MIDI devices is in a form called a MIDI message, which encodes aspects of sound such as:• note played, note number, velocity

• sustain pedal, breath controllers, aftertouch, pitch bend, modulation

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MIDI Message FormatMIDI Message Format

Control messages are sent as groups of bytes, preceded by one start bit and followed by a stop bit

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MIDI Message FormatMIDI Message Format

There are two basic types of MIDI message byteStatus byte (starts with a ‘1’)Data byte (starts with a ‘0’)

1sssnnnn 0xxxxxxx 0yyyyyyy

8 bits

Status Data 1 Data 2

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MIDI Message FormatMIDI Message Format

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MIDIMIDIThere are sixteen basic MIDI channels and

instruments can usually be set to receive on one (omni off) or all (omni on)

General MIDI sets the standard for the ordering and naming of sounds

• Group 1-8 Piano 65-72 Reed

9-16 Chromatic Percussion 73-80 Pipe 17-24 Organ 81-88 Synth Lead 25-32 Guitar 89-96 Synth Pad 33-40 Bass 97-104 Synth FX 41-48 Strings 105-112 Ethnic

Instruments 49-56 Ensemble 113-120 Percussive

Instrms 57-67 Brass 121-128 Sound

effects

• Plus 47 percussive sounds

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MIDIMIDI

Using MIDI for transferring music can be problematic

Even with general MIDI the output depends on the quality and type of synthesiser usedNot so good for Hi-FiVery good for multimedia or games sound

effects and music

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MIDI SequencersMIDI Sequencers

Capable of storing a number of “tracks” of MIDI information and manipulating them

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MIDI SequencersMIDI Sequencers

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MIDI SequencersMIDI Sequencers

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FinFin

Fin