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Digital Audio

Digital Audio. Data dan Teknologi Multimedia Sesi 05 Nofriyadi Nurdam. Learning Outcomes. At the end of this session, the students will be able to: Show how to use sound on multimedia application. Course Outlines. Sound Definition Analogue to Digital Converter (ADC) Digital Audio

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Digital Audio

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  1. Digital Audio Data dan Teknologi Multimedia Sesi 05 Nofriyadi Nurdam

  2. Learning Outcomes At the end of this session, the students will be able to: • Show how to use sound on multimedia application.

  3. Course Outlines • Sound Definition • Analogue to Digital Converter (ADC) • Digital Audio • MIDI (Musical Instrument Digital Interface) • Working with Sound

  4. Sound Sound are rapid vibrations that are transmitted as variations in air pressure Sound comprises the spoken word, voices, music and even noise.

  5. Sound As the sound vibrates it bumps into molecules of the surrounding medium causing pressure waves to travel away from the source in all directions Types of Sound in Multimedia: Speech Music Sound Effect

  6. Waveforms • Sound waves are manifest as waveforms • A waveform that repeats itself at regular intervals is called a periodic waveform • Waveforms that do not exhibit regularity are called noise • The unit of regularity is called a cycle • This is known as Hertz (or Hz) after Heinrich Hertz • One cycle = 1 Hz • Sometimes written as kHz or kiloHertz (1 kHz = 1000 Hz)

  7. Waveforms Time for one cycle distance along wave Cycle

  8. The characteristics of sound waves

  9. The characteristics of sound waves Frequency • the rate at which sound is measured • Number of cycles per second or Hertz (Hz) • Determines the pitch of the sound as heard by our ears • The higher frequency, the clearer and sharper the sound  the higher pitch of sound • Amplitude • Sound’s intensity or loudness • The louder the sound, the larger amplitude. • In addition, all sounds have a duration and successive musical sounds is called rhythm

  10. The characteristics of sound waves Time for one cycle Amplitude distance pitch along wave Cycle

  11. Piano Pan flute Snare drum Example waveforms

  12. Air pressure variations Digital to Analogue Converter Captured via microphone Converts back into voltage Signal is converted into binary(discrete form) 0101001101 0110101111 DAC ADC Analogue to Digital Converter Air pressure variations Capture and playback of digital audio

  13. The Analogue to Digital Converter (ADC) An ADC is a device that converts analogue signals into digital signals An analogue signal is a continuous value It can have any single value on an infinite scale A digital signal is a discrete value It has a finite value (usually an integer) An ADC is synchronised to some clock It will monitor the continuous analogue signal at a set rate and convert what it sees into a discrete value at that specific moment in time The process to convert the analogue to digital sound is called Sampling. Use PCM (Pulse Code Modulation) When you present the sound wave as numbers, the process is called digitizing and the result will become digital audio

  14. Digitized Sound 0110101110110110101101101101110110111101101110110110111011110110110101010001011011011010110110100110110110110110110110101010101001100110010010011001100110100110101110110110101101101101110110111101101110110110111011110110110101010001011 Is a sampled sound. Every nth fraction of a second, a sample of sound is taken and stored as digital information

  15. Digital Sound Quality Quality of digital sound depends on

  16. Digital sampling - Sampling Rate

  17. Digital sampling - Sampling Rate

  18. Sampling Parameters • Sampling Rate • Frequency of sampling • Measure in Hertz • The higher sampling rate, higher quality sound but size storage is big. • Standard Sampling rate: • 48.000 kHz (DAT) - Digital Audio Tape, also DVD • 44.100 kHz (CD) - Compact Disk - typical quality of most sound cards • 22.255 kHz - Medium quality • 11.025 kHz - Low quality (frequently used for speech)

  19. Sampling Parameters • Size sample • The resolution of a sample is the number of bits it uses to store a given amplitude value, e.g. • 8 bits (256 different values) • 16 bits (65536 different values) • A higher resolution will give higher quality but will require more memory (or disk storage)

  20. Size sample

  21. Quantisation • Samples are usually represented the audio sample as a integers(discrete number) or digital

  22. Calculating the size of digital audio • The formula is as follows: • The answer will be in bytes • Where: • sampling rate is in Hz • Duration/time is in seconds • resolution is in bits (1 for 8 bits, 2 for 16 bits) • number of channels = 1 for mono, 2 for stereo, etc.

  23. Calculating the size of digital audio • Example: • Calculate the file size for 1 minute, 44.1 KHz, 16 bits, stereo sound • Where: • sampling rate is 44,100 Hz • duration/time is 60 seconds • resolution is 16 bits • number of channels for stereo is 2 44100 * 60 * 16 *2 8

  24. Digital audio editing software • One of the most powerful and professional PC-based software is previously known as Cool Edit. It’s now known as Adobe Audition. Same program, new company.

  25. Editing Digital Audio • Simple audio editing software allows: • Recording of digital audio segments • Trimming • Splicing and assembly • Volume adjustments of the entire segment • Reversing Sounds • Copy, cut, paste and delete segments of digital audio • Others audio editing software: • Sound Forge • Gold Wave • PROSONIQ SonicWORX • Samplitude Studio

  26. Audio formats • .WAV (Developed by IBM and Microsoft) • .AU (UNIX) • .AIFF (Audio Interchange File Format) • .MP3 (MPEG layer 3) • .SND (Mac) • .RA (RealAudio) • .WMA (Windows Media Audio) • .VOC (SoundBlaster)

  27. MIDI (Musical Instrument Digital Interface) • MIDI is a standard for specifying a musical performance • It allows different electronic devices to communicate together – Rather than send raw digital audio, it sends instructions to musical instruments telling them what note to play, at what volume, using what sound, etc. • The synthesiser that receives the MIDI events is responsible for generating the actual sounds. Example: Keyboard Piano • MIDI data is not digitized sound: it is a shorthand representation of music stored in numeric form

  28. MIDI Setup

  29. A MIDI sequencer allows musicians to edit and create musical compositions like a word processor Cut and paste Insert / delete MIDI sequencers

  30. Advantages of MIDI • MIDI files are compact; the size of the file is completely independent of playback quality • In some cases MIDI may sound better than digital audio (if the MIDI sound source is of high quality) • MIDI data is completely editable: you can change the length of a MIDI file by varying its tempo without changing the pitch • Still used a lot in studio environment to connect synthesizers and other equipment

  31. Disadvantages of MIDI • MIDI does not represent sound but musical instruments, so playback is very rarely accurate (usually same score, wrong instrument) • MIDI cannot easily be used to play spoken dialog • An old format, people have already begun forgetting it

  32. MIDI VS Wav

  33. How audio can be used effectively • Cautions and warnings • It is a good medium for alerting users to critical information. Some uses include: • Sounding an alarm when a limit is reached • Alerting users when data is entered incorrectly • Music and Sound Effects • These make multimedia interaction more real. Some uses include: • Musical background for a video segment • Birds Songs accompanying photographs in biological field training

  34. How audio can be used effectively • Sound-related data. • Some uses include: • Helping mechanics diagnose engine trouble • Training medical students to recognize different breathing sounds • Direct voice communication. • Some uses include: • Leaving a voice message for other users of an application • Consulting with an expert during a troubleshooting procedure.

  35. Advantages and Disadvantages of using audio • Sound adds life to any multimedia application and plays important role in effective marketing presentations • Advantages • Ensure important information is noticed • Add interest • Can communicate more directly than other medi • Disadvantages • Easily overused • Requires special equipment for quality production • Not as memorable as visual media

  36. Adding Sound to Multimedia Project Determine the sound playback capabilities that the end user’s system offers Decide what kind of sound is needed and where you’ll use them Decide when to use midi and when to use digital audio Acquire source material Edit the sounds to fit your project Test the sounds to be sure they are timed properly

  37. Adding Sound to Multimedia Project • Decide what kind of sound is needed and where you’ll use them • Decide when to use midi and when to use digital audio • Acquire source material • Edit the sounds to fit your project • Test the sounds to be sure they are timed properly

  38. Q & A

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