Audio 1

Subject : T0934 / Multimedia Programming FoundationSession : 8Tahun : 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 digitization and enhancement

– Identify Java Sound API syntax to manipulate basic audio properties

Outline

• Audio Digitization• MIDI• Audio Quantization and Transmission• Java Sound API

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A Typical Audio Architecture

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Sound

• Sound are rapid vibrations that are transmitted as variations in air pressure

• To use sound digitally, we must digitize (converse to a stream of numbers) the analog sound first

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Amplitude

Analog signal of sound

Analog signal of sound

Sound Digitization

• To fully digitize the sound, we have to sample in Time (Sampling) and in Amplitude (Quantization)

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Sampling

Quantization

Sampling

• Sampling– Measuring at evenly spaced intervals

• Sampling Rate– Known as sampling frequency, measured in Hertz (Hz)

• Nyquist Rate– To have a correct sampling, sampling rate should equal

to at least twice the maximum frequency– If sampling rate is lower than Nyquist rate, it will result

in false (alias) frequency

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Quantization

• Sampling in the amplitude dimension, represented in fixed numbers of bits (8, 12, or 16 bits)

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• Results in a loss of precision which is called distortion (or called quantization noise)

• Dithering (adding random noise to quantized audio) can be used to remove some of the distortion

Common Rates

Quality Sample Rate (kHz)

Quantization

Mono/Stereo

Frequency Range

Telephone 8 8 Mono 200-3400

AM Radio 11,025 8 Mono 100-5500

FM Radio 22,05 16 Stereo 20-11000

CD 44,1 16 Stereo 5-20000

DAT 48 16 Stereo 5-20000

DVD audio 192 (max) 24 (max) Up to 6 channels

96000 (max)

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Sampled Audio Format

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File Type

Acronym For

Originally Created By

Type of Compression

Platforms

.aiff Audio Interchange File Format

Apple, adopted later by Silicon Graphics

usually not compressed, but has a compressed version

Apple Macintosh and Silicon Graphics computers, and now also on Windows

.wav IBM and Microsoft

supports a number of different compression formats

primarily for Windows, but can be run on in other systems

.au and .snd

Also called mu-law or Sun mu-law format

Sun and NeXT mu-law encoding compresses the file at a ratio of 2:1; slow decompression

Sun, NeXT, Unix or Linux operating system

.mp3 MPEG audio layer 3

Moving Pictures Experts Group

good compression rate with high quality sound

cross-platform

Synthesizing Sounds

• Frequency Modulation (FM)– Producing new audio signal using a source waveform’s

frequency is changed by a modulating frequency– Based on the same principles used for FM radio

trasmission– Used in low-end versions of Creative Sound Blaster PC

sound card

• Wave-Table– More accurate way reproducing sound– Using actual samples of real instruments– More expensive than FM synthesis (partly because of

larger data storage)

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MIDI

• Musical Instrument Digital Interface• A scripting language that codes

events (MIDI messages + timings)• Enable computers, synthesizers,

keyboards, and other musical devices to communicate with each others.

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A Possible MIDI Configuration

Bina Nusantara http://java.sun.com/docs/books/tutorial/sound/index.html

Synthesizers

• A sound generator that can vary pitch, loudness, and tone color.

• Now included on PC sound cards. The units that generate sound are called tone/sound modules.

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Sequencers

• In the beginning, a special hardware device for storing and editing a sequence of musical events (MIDI data)

• Now, a software music editor on the computer

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MIDI keyboards

• A keyboard that produces MIDI messages, not sound

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MIDI Messages

• Sequences of MIDI instructions

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Channel Messages

• Voice Messages – Sends information of which note to play– Used to control sustain, vibrato, tremolo, and pitch

• Mode Messages– Determines how an instrument processes MIDI voice

messages (to respond all messages, respond just to correct channel, don’t respond at all, etc)

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System Messages

• For commands that are not channel-specific

• Common messages– Relates to timing or positioning

• Real-time messages– Relates to synchronization

• Exclusive messages– Included so manufacturers can extend the MIDI standard

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MIDI standard

• General MIDI (GM1)– Standard for assigning instruments to patch numbers so MIDI

music can sound more or less the same on every machine– Ex : patch no.1 = piano

• General MIDI level 2 (GM2)– Extended General Midi, with SMF (Standard MIDI File) format

defined.– Includes extra character of information such as karaoke lyrics– Increases the number of available sounds – Increases the amount of control available for sound editing

and musical performance

• General MIDI Lite (GML)– For mobile applications

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Standard MIDI Files

• a digital file that contains MIDI events

• was developed in 1990 for file exchange between MIDI sequencers

• The information in a standard MIDI file is referred to as a sequence

• contains one or more tracks which each typically contains the notes of a single instrument

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Java Sound API

• Supports both sampled audio and MIDI data

• javax.sound.sampled– This package specifies interfaces for capture, mixing,

and playback of digital (sampled) audio.

• javax.sound.midi– This package provides interfaces for MIDI synthesis,

sequencing, and event transport.

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Playing Sound

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Full code downloadable in Additional Materi.

Playing MP3

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Create mp3 player

Open MP3 file and start player

Playing MP3

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Getting controller component

Result

Note : This program use JMF to play MP3 file.

Full code is downloadable in Additional Materi

Playing WAV

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Create player from file

Open WAV file

Getting music length

Playing WAV

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Setting control for control the music

Playing MIDI

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References

• Basics of Digital Audio. 2001. http://www.cs.cf.ac.uk/Dave/Multimedia/node143.html

• Developing a Strategy for Creating and Assessing Digital Media Curriculum Material. 2004. http://imej.wfu.edu/articles/2004/1/01/

• Midi. 2008. http://www.midi.org/• Trail: Sound. 2008.

http://java.sun.com/docs/books/tutorial/sound/index.html

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

• Sound. 2009. http://en.wikipedia.org/wiki/SoundBina Nusantara