Understand the basic principal of audio format

Audio 2
Subject
Session
Tahun
Versi
:
:
:
:
T0934 / Multimedia Programming Foundation
9
2009
1/0
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
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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
Input analog
signal
Output analog
signal
•
•
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Bandlimiting
filter
Mu-law/A-law
compressor
Linear PCM
Low-pass filter
Mu-law/A-law
decompressor
Digital to
analog
converter
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
• 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
identifies the file
as a WAV file
fmt chunk
describes the sound
data's format such as :
• type of compression
• number of channels
• sample rate
• bits per sample
• other attributes
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data chunk
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
Layer 1
• Digital Audio Tape
Layer 2
• Proposed for use in digital audio broadcasting
Layer 3 (MP3)
• Originally aimed at audio transmission over ISDN lines
• Common digital audio format compression
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MPEG-1 audio Format
Header
•
•
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Synchronization code
Sampling rate
Bitrate
Stereo information
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SBS Format
SBS
Ancillary data
(subband-samples)
(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
Midi File
- Get duration
Sampled Sound File
- Get duration
- Get Audio Format
- Get Sample Rate
- Get Channels
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Sample Code
To Play Midi
To Play Sampled Sound
To Control Volume and Balance Sampled Sound
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Sample Code
Create JSlider to control Balance and Volume Sampled Sound
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Sample Code
Result
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References
• WAVE PCM soundfile format. 2003.
http://ccrma.stanford.edu/courses/422/projects/WaveFor
mat/
• WAV File Format. 2009.
http://technology.niagarac.on.ca/courses/ctec1631/WavF
ileFormat.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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