Pengantar Multimedia

Sound  Physical phenomenon – vibration.  Source = electrical – acoustic  Vibration – oscillation – wave  Wave periodical – song, musical instrument non periodical – explosion, cough Vibration Diff Air pressure Travels through medium Receptor

 Periodical – has the same pattern over a certain interval

 Speed of sound depends on the medium that the waves pass through depends on the property of a material Air, sea level, 20° = 343m/s (most common) Water, 20° = 1,482 m/s Steel = m/s

Frequency  The amount of period in 1s.  Hertz / cycles per second (cps)  Wavelength = sound speed (c) / frequency (f)  eg. A wave of 20 kHz with 343m/s has wavelength.  343/20 = 17,15.

 Based on the frequency Infrasound 0 Hz - 20 Hz Audible Sound20 Hz - 20 KHz Ultrasound20 KHz - 1 GHz Hypersound1 GHz - 10 THz  Sound created by human = 50 Hz – 10KHz  Musical Sound = 20 Hz – 20 KHz  Multimedia system must use audible sound.

 Audible sound is called Audio and the wave is called Acoustic Signal.  In connection to Audio, all sound frequencies except Audio is called Noise.

ADC  Device that converts a continuous physical quantity (usually voltage) to a digital number that represents the quantity's amplitude.  Digital sampling : Measuring the analog signal at regular intervals. Eg. Audio CD with 44100Hz has sample of 44100/s.

 Application Music Recording. Current ADC converter can sample at rates up to 192KHz. DSP (Digital signal processing). TV tuner cards use fast ADC. Slow ADC might be used in 8, 10, 12, or 16-bit microcontrollers. Digital Imaging, uses ADC to converts colors into data stream.

DAC  Converts digital data (usually binary) into an analog signal (current, voltage, or electric charge).  Unlike analog signals, digital data can be transmitted, manipulated, and stored without degradation, albeit with more complex equipment.

 Application Audio = Most modern audio signals are stored in digital form (MP3, MP4), so we need CD Player, Digital Music Player, PC sound cards. In VoIP (Voice over IP) applications, the source must first be digitized for transmission, so it undergoes conversion via an analog-to-digital converter, and is then reconstructed into analog using a DAC on the receiving party's end.

Audio Format Development

Audio File .3gp = multimedia container format can contain proprietary formats .act = ACT is a lossy 8 Kbit/s compressed audio format recorded by most Chinese MP3 and MP4 players with a recording function, and voice recorders. .aiff = standard audio file format used by Apple. It could be considered the Apple equivalent of wav. .aac = the Advanced Audio Coding format is based on the MPEG-2 and MPEG-4 standards. .amr = AMR-NB (adaptive Multi Rate – Narrow Band) audio, used primarily for speech.

.ape = Monkey's Audio lossless audio compression format. .au = the standard audio file format used by Sun, Unix and Java. .awb = AMR-WB audio, used primarily for speech. .dct = A variable codec format designed for dictation. It has dictation header information and can be encrypted (as may be required by medical confidentiality laws). .dss = Olympus proprietary format (old and poor). .dvf = a Sony proprietary format for compressed voice files; commonly used by Sony dictation recorders. .flac = File format for the Free Lossless Audio Codec, a lossless compression codec.

.gsm = designed for telephony use in Europe with very practical format for telephone quality voice. .iklax = An iKlax Media proprietary format, a multi-track digital audio format allowing various actions on musical data, for instance on mixing and volumes arrangements. .ivs = developed by 3D Solar UK Ltd for use in music downloaded from their Tronme Music Store and interactive music and video player. .m4a = MPEG-4 audio, used by Apple for unprotected music downloaded from their iTunes Music Store .m4p = version of AAC with DRM developed by Apple for use in music downloaded from their iTunes Music Store.

.mmf = a Samsung audio format that is used in ringtones. .mp3 = MPEG Layer III Audio. Is the most common sound file format used today. .mpc = Musepack (formerly known as MPEGplus, MPEG+ or MP+) is an open source lossy audio codec. .msv = a Sony proprietary format for Memory Stick compressed voice files. .ogg =.oga (rare) = a free, open source container format supporting a variety of formats, the most popular of which is the audio format Vorbis. Vorbis offers compression similar to MP3 but is less popular. .Opus = a lossy audio compression format developed by the Internet Engineering Task Force (IETF).

.ra =.rm = a RealAudio format designed for streaming audio over the Internet. .raw = a raw file can contain audio in any format but it is rarely used except for technical tests. .sln = Signed Linear format used by Asterisk. .tta = The True Audio, real-time lossless audio codec. .vox = the vox format most commonly uses the Dialogic ADPCM (Adaptive Differential Pulse Code Modulation) codec. .wav = standard audio file container format used mainly in Windows PCs. Commonly used for storing uncompressed (PCM), CD-quality sound files, which means that they can be large in size—around 10 MB per minute.

.wma = Windows Media Audio format, created by Microsoft. Designed with Digital Rights Management (DRM) abilities for copy protection. .wv = format for wavpack file. .webm = Royalty-free format created for HTML5 video.

MIDI  Musical Instrument Digital Interface.  A protocol that enables computers, synthesizers, keyboards, and other musical devices to communicate with each other.  Small file size.