Transcript Audio Technology

Audio Technology
Ozzi Suria S.T., M.T.
What is sound?
• Sound is a physical phenomenon caused by vibration of material.
• Example: guitar strings
• The vibration triggers pressure wave fluctuations in the air around
the material
• The wave form occurs repeatedly at regular intervals or period
• Sound is represented as analog signal with continuous curve of
sound wave
Frequency
• Frequency (f) represents number of periods per second
• Measured in Hertz (Hz)
• Example:
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Infrasonic
Audiosonic
Ultrasonic
Hypersonic
: 0 to 20 Hz
: 20 Hz to 20 kHz
: 20kHz to 1 GHz
: 1 GHz to 10 THz
• Human’s ear frequency is 20Hz to 20kHz
f = 1/T
Keterangan:
T = Periode
Amplitude
• Amplitude is a measure to deviate the pressure wave from its mean
value.
Audio Representation on Computers
• Analog signal must be converted to Digital signal using Analog-toDigital Converter (ADC)
• The computer has to measure the wave’s amplitude in regular time
intervals
• Then, generates a sequence of sampling values or samples for short.
Sampling Rate
• Sample rate is the number of samples of audio carried per second,
measured in Hz or kHz.
• Example of Audio Sample Rate:
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44100 Hz – CD Quality
48000 Hz – DVD Quality
96000 Hz
128000 Hz
Bit Rate & Bit Depth
• Bit rate is the number of bits per second that can be transmitted
along a digital network
• Example of Audio Bit Rate:
• 128 kbps
• 192 kbps
• 256 kbps
• Bit depth is the number of bits of information in each sample, and it
directly corresponds to the resolution of each sample.
• Example of Audio Bit Depth
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8 bit  28 = 256 level
16 bit  216 = 65.536 level
24 bit
32 bit
• Higher value of audio bit depth = Better audio quality & more size
Audio Size Calculation
• Mono
Sampling Rate (Hz) * Audio Time (seconds) * (Bit Depth/8) * 1
• Stereo
Sampling Rate (Hz) * Audio Time (seconds) * (Bit Depth/8) * 2
The result always in byte.
Practice
1. Hitunglah berapa ukuran file dalam satuan (byte)
dari file audio yang direkam secara stereo selama
3 menit, dengan sampling rate 44100 Hz dan
resolusi 16 bit!
2. Hitunglah ukuran tersebut dalam satuan Mega
Byte!
3. Hitunglah Bit Rate dari audio tersebut!
Practice Answer
1. Size:
• 44100 * (3 * 60) * (16/8) * 2 = 31.752.000 Byte
2. Ukuran dalam MB:
• 31.752.000 / 1024 = 31.007,8125 Kilo Byte
• 31.007,8125 / 1024 = 30,281 Mega Byte
3. Bit Rate (Byte/s):
• 2 * 44100 * 16/8 = 176.400 byte/s
Music & MIDI Standard
• On Paper, music described as full scores (not balok)
• Computers and electronic musical instruments
employ Musical Instrument Digital Interface (MIDI).
• MIDI Standard defines how to code all musical
scores elements, such as sequences of notes, timing
conditions, and the instrument to play each note.
Advantage of MIDI
• Universal playback.
• Easy integration into existing HTML pages using a standard text
editor.
• Availability of mature authoring tools
• The smallest file size per minute of any audio format. (An entire
minute of MIDI results in a mere 10 KB to 20 KB file, compared to a
one-minute 500 KB MP3 file or a 120 KB 28.8 Kbps RealAudio file)
Tugas
• Carilah perbedaaan kualitas suara yang dihasilkan oleh audio dengan
sinyal analog dan sinyal digital!
• Poin yang dapat dibahas:
• Definisi sinyal analog dan sinyal digital
• Cara kerja sinyal analog dan digital
• Kelebihan dan Kekurangan Masing-Masing
• Tugas diketik, dikerjakan berkelompok (3-4 orang)
• Dikumpulkan: Kamis, 7 April 2016 (saat kuliah)
Reference
• Steinmetz R. & Nahrstedt K., 2002, Multimedia Fundamentals,
Prentice Hall PTR