Audio 2

Subject : T0934 / Multimedia Programming FoundationSession : 9Tahun : 2009Versi : 1/0

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Learning Outcomes

In the end of this session, students must be able to: – Understand the basic principal

of audio format and compression

– Apply Java Sound API syntax to manipulate basic audio properties

Outline

• Audio Coding• Audio Compression• Java Sound API

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PCM

• PCM (Pulse Code Modulation) quantized sample output– Differences versions is called DPCM – Much-simplified version of DPCM is called DM (Delta

Modulation– Adaptive version is called ADPCM

• PCM encodings – Linear quantization – Non-linear quantization

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Linear quantization

• samples are typically stored as uniformly quantized values

• Compact discs, for example, use linear PCM-encoded sound.

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Non-linear quantization

• maps the original sound's amplitude to the stored value using a nonlinear function

• Mu-law encoding and A-law encoding are common nonlinear encodings, usually used for telephony or recordings of speech.

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PCM Coding Process

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Input analog signal

Output analog signal

• Bandlimiting filter• blocks out very low and high frequencies

• Low-pass filter• allows only frequencies up to the original signal to

be retained

• Bandlimiting filter• blocks out very low and high frequencies

• Low-pass filter• allows only frequencies up to the original signal to

be retained

WAVE format

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• The WAVE file format uses Microsoft's RIFF (Resource Interchange File Format) standard for the storage of multimedia files.

• A RIFF file starts out with a file header followed by a sequence of data chunks.

RIFF header chunk

RIFF header chunk fmt chunkfmt chunk data chunkdata chunk

identifies the file as a WAV file

describes the sound data's format such as :

• type of compression• number of channels• sample rate• bits per sample• other attributes

contains the size of the data and

the actual sound

MPEG-1 audio

• Has three layers of audio compression

• The higher layers, the better compression

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MPEG-1 audio Format

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• Synchronization code

• Sampling rate• Bitrate• Stereo information

HeaderHeader SBS FormatSBS Format SBS(subband-samples)

SBS(subband-samples)

Ancillary data(extra information)Ancillary data

(extra information)

• Multilingual data• Surround-sound

data

MPEG-2/4/7

• MPEG-2– Standard for DVD– MPEG-2 Advanced Audio Coding (AAC) can have five

channels (5.1 channel systems)

• MPEG-4– Integrates several different audio components into one

standard– Audio components include speech compression, text-to-

speech, and MIDI

• MPEG-7– Promotes ease of search for audio objects– Supports ASR (Automatic Speech Recognition)

application

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Java Sound API

• Play and stop sampled audio• Volume up and down• Right and left channel balance• Play and stop MIDI

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Sound Property

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- Get durationMidi File

Sampled Sound File

- Get Audio Format

- Get duration

- Get Sample Rate

- Get Channels

Sample Code

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To Play Sampled Sound

To Control Volume and Balance Sampled Sound

To Play Midi

Sample Code

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Create JSlider to control Balance and Volume Sampled Sound

Sample Code

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Result

References

• WAVE PCM soundfile format. 2003. http://ccrma.stanford.edu/courses/422/projects/WaveFormat/

• WAV File Format. 2009. http://technology.niagarac.on.ca/courses/ctec1631/WavFileFormat.html

• The Java Sound API. 2009. http://onjava.com/onjava/excerpt/jenut3_ch17/

• MP3. 2009. http://en.wikipedia.org/wiki/MP3• WAV. 2009. http://en.wikipedia.org/wiki/WAV

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