CHAPTER 06: AUDIO TECHNOLOGY

1. CHAPTER 06: AUDIO TECHNOLOGY • Introduction to Audio • Converting Process of Analog Audio Into Digital Audio • Manipulating Processes of Digital Audio • MIDI Audio Last updated: 5/07/06

2. Introduction to Audio • Vibrations in the air create waves of pressure that are perceived as sound. • Sound waves vary in sound pressure level (amplitude) and in frequency or pitch. • Acoustics – a branch of physics, studies sound. • Sound is measured in à dB (decibel), which is the ratio between a chosen reference point on a logarithmic scale and the level that is actually experienced.

3. Introduction to Audio • Sound gives multimedia products a dimension that transcends other computer applications. • It acts as a notice or a warning that something is happening. • System sounds are assigned to various system events such as startup and warnings, among others. • Macintosh provides several system sound options such as glass, indigo, laugh. • In Windows, available system sounds include start.wav, chimes.wav, and chord.wav. • Multimedia sound is either digitally recorded audio or MIDI (Musical Instrumental Digital Interface) music.

4. Introduction to Audio • Most of today’s desktop computers are sound-capable machines. • We can store and manipulate many kinds of different sounds such as the spoken words, music, and artificially generated sounds such as synthesized music.

5. Introduction to Audio Characteristics of Sound and Digital Audio • Sound comprises the spoken word, voices, music and even noise. • It is loud and soft, deep and shrill. • Sound is based on 2 things: 1. Energy 2. Transport medium • Energy from a banging drum is converted into pressure that is transmitted by the air. • Sound is actually created when air pressure is varied.

6. Introduction to Audio • The change in air pressure is detected by the ear drum and a vibration occurs that is sensed by nerves that carry electrical signals to the brain. • 2 characteristics of sound waves : 1. Amplitude 2. Frequency 1. Amplitude • Amplitude / sound pressure is the power or intensity (loudness) of the sound. • The louder the sound,the larger the amplitude.

7. Introduction to Audio 2. Frequency • Frequency or pitch is the rate at which sound is measured (the distance between the peaks), in cycles per second or Hertz(Hz). • A pattern that recurs every second is equal to 1 Hz. • The higher the frequency,the clearer and sharper the sound.

8. Introduction to Audio Measuring Audio Quality • All digital audio is not created equal. The quality of digital audio is measured according to 2 basic parameters: 1. Resolution 2. Sampling rate 1. Resolution • Determines the number of bits used to represent the dynamic range. • It is the difference between the loudest and the softest sounds. It is measured in bits.

9. Introduction to Audio 2. Sampling rate • Sampling rate determines the frequency make-up of the recording. • The three sampling frequencies most often used in multimedia are CD-quality 44.1 kHz, 22.05 kHz and 11.025 kHz. • Recording at a high sampling rate produces a more accurate capture of the high frequency content of the sound. • Two most common sample sizes are 8 bits and 16 bits. • An 8-bit sample allows 256 values that are used to describe the sound, whereas 16-bit sample provide 65,536 values.

10. Introduction to Audio • Recording resolution determines the accuracy with which a sound can be digitized. • The greater the number of bits used in a recording, the more realistic the sound playback. Channel • When considering sound quality and realism, stereo recording may be the choice because stereo recordings are lifelike and realistic. • Mono sounds are less realistic, flat and not so dramatic, but they take up less room on disk than stereo files. Mono sound packs all sound in only one channel.

11. Sample Rate Bit value Size of File 44.1 kHz 16 1.76 MB 44.1 kHz 8 882 KB 22.05 kHz 16 882 KB 22.05 kHz 8 440 KB 11.025 kHz 8 220 KB Introduction to Audio Size of monophonic (bytes) = Number of channel (1) * Sampling rate in Hertz * Time in seconds * Bytes used • Stereo sounds require twice the space as mono recordings because stereo format uses two or more recording channels to produce more realistic sounds. Size of stereo (bytes) = Number of channel (2) * Sampling rate in Hertz * Time in seconds * Bytes used Table A: File size of 10 seconds of digitized audio in stereo

12. Introduction to Audio Calculate the file size for 1 minute, 44.1 Khz, 16 bit, with stereo sound. Number of channel(c) = 2 (stereo) Time(t) = 60 seconds Sampling rate(s) = 44,100 Hz (frequency) Byte(b) = 2 bytes File size = 2 * 60 * 44,100 * 2 = 10,584,000 bytes

13. Converting Processes Of Analog Audio Into Digital Audio • Digital Sound is produced by sampling sound waves over time. A digitized sound files consist of sampled amplitudes of a sound wave at a number of discrete time interval. • The devices that perform the sampling of an analog wave to produce such as a digital file are called analog-to-digital converters (ADCs). • The devices that perform the opposite transformation are called digital-to-analog converters (DACs) and they reconstruct an analog wave for playback from digital file. • When we sample a sound wave, we usually place the discrete sample times equal distances apart along the time axis.

14. Converting Processes Of Analog Audio Into Digital Audio • This is called a sampling rate. Sampling rates are usually expressed in Hertz. • In addition to sampling rate, the resolution, or the amount of computer memory used to store individual amplitude samples, also affect the fidelity of digital music playback. • To use a personal computer for digitizing sound, you must have a microphone attached to an ADC and a connection to allow you to store the values produced by the ADC in your computer’s memory and on disk. • This may require a digital audio capture card that can be installed on one of your computer’s internal expansion slots.

15. Converting Processes Of Analog Audio Into Digital Audio File Formats These different file formats are available to store digital audio and MIDI data: Audio Interchange File Format (AIFF, AIF) • Used by Macintosh, IBM compatibles, Commodore Amiga, Silicon Graphics machines. • A large number of sampling rates (up to 32 bits) is supported Musical Instrument Digital.

16. Converting Processes Of Analog Audio Into Digital Audio Interface (MID, MDI, MFF) Internationally accepted file format to store MIDI data. Resource Interchange File Format (RIFF) • Developed by Microsoft. • Contain a variety of types of data including digital, audio and MIDI. Sound (SND) • Developed by Apple. • Limited to a sampling rate of 8 bits.

17. Converting Processes Of Analog Audio Into Digital Audio Roll (ROL) • Developed by Adlib Inc. • Used with its sound cards. • Stores MIDI-like data and Yamaha FM synthesizer information. Wave (WAV) • Widely supported by Windows applications. • Developed by Microsoft as a subset of the RIFF.

18. Converting Processes Of Analog Audio Into Digital Audio Sun Audio (AU) • Developed and used by Sun Micro Systems workstation. • 16-bit compressed audio format. Voice (VOC) • Developed for the Sound Blaster audio card from Creative Technology. • Support sampling rates of 8 and 16 bits with or without compression.

19. Converting Processes Of Analog Audio Into Digital Audio Turtle SMP (SMP) • Developed by Turtle Beach Systems. • For audio recording and editing software. Software for Recording Digital Audio Macintosh Windows

20. Manipulating Digital Audio Files • Before capturing or record any audio source, ponder 3 crucial considerations: • Balancing the need for audio quality with available RAM and hard disk resources. • Selecting the most adequate recording level for a good clean recording. • Balancing audio quality with processing speed and sampling rate capability of the recording computer and the playback computer.

21. Manipulating Digital Audio Files • These considerations determine the file size and quality of the recording. Different editing operations can be performed on an audio file: 1. Trimming 2. Splicing and assembly 3. Volume adjustment 4. Fade-ins and fade-outs 5. Resampling or down sampling 6. Mixing audio 7. Format conversion 8. Equalization 9. Time stretching 10. Reversing sounds 11. Digital signal processing

22. Manipulating Digital Audio Files Trimming • Deleting dead space (areas without sound) at the beginning and end of the recording. • Trimming a couple of seconds can significantly decrease file size. Splicing and assembly • If you hear extraneous noise when play back the recorder audio, you may want to identify the locations of the extraneous noise in the wave front to select and then cut it. Volume adjustment • To increase or decrease the volume of an entire sound, clip, or a segment of it.

23. Manipulating Digital Audio Files Fade-ins and fade-outs • Called enveloping. • Can fade-in or fade-out a highlighted section of the audio file. • To fade out, take the handle at the end of the line and move it down to the button of the screen. Resampling or down sampling • On a number of occasions, you may use sampled and recorded 16-bit audio files, but because of file size considerations or sound quality output, you need to down sample the file (turn a 16-bit file into an 8-bit file)

24. Manipulating Digital Audio Files Mixing audio • Most sound-capturing and editing software allows you to mix two or more audio files. • Determine the audio files to mix and decide whether the new file will be stereo or mono. Format conversion • Changing the file format to move audio between computer systems or changing data formatting (file header). Equalization • Used to clean up noise by reducing spikes or levels within the audio data stream.

25. Musical Instrument Digital Interface (MIDI) • MIDI stands for Musical Instrument Digital Interface. It was developed in the 1980s as a communications standard for electronic music instruments. • On the Macintosh, digitized sounds may be stored as data files, resources, or applications such as AIFF or AIFC. • In Windows, digitized sounds are usually stored as WAV files. • Devices translating music into digital form representing notes to be played, instruments that play the notes, their volume and their length.

26. Musical Instrument Digital Interface (MIDI) • Their controller devices are such as: • Electronic keyboards • Guitars • Drum machines • Users need a synthesizer to translate information generated by the MIDI device into sound. MIDI systems do not record the actual sounds in the digital file, the resulting sound file is much smaller than digital audio. • One minute MIDI music requires 6K. • 5 minutes 30K = MIDI • Digital Audio = 50K

27. Musical Instrument Digital Interface (MIDI) • There are advantages and disadvantages to use MIDI over digital audio: • consistency in audio quality • compatibility • processor speed requirement • file size • Most synthesizers have the following common components: • Sound Generators • Microprocessor • Keyboard • Control Panel • Auxiliary Controllers • Memory

28. Musical Instrument Digital Interface (MIDI) MIDI Versus Digital Audio • MIDI is analogous to structured or vector graphics, while digitized audio is analogous to bitmapped images. • MIDI is device dependent while digitized audio is device independent. • MIDI files are much smaller than digitized audio. • MIDI files sound better than digital audio files when played on a high-quality MIDI device.

29. Musical Instrument Digital Interface (MIDI) MIDI Software • Once a computer is connected to a MIDI system, a variety of MIDI applications can run on it. • Digital computers afford the composer or sound designer unprecedented levels of control over the evolution and combination of sonic events. • The software applications generally fall into four major categories: • Music recording and performance applications. • Musical notations and printing applications. • Synthesizer patch editors and librarians. • Music education applications.

30. Musical Instrument Digital Interface (MIDI) • With MIDI, it is difficult to playback spoken dialog, while digitized audio can do so with ease. • MIDI does not have consistent playback quality while digital audio provides consistent playback quality. • One requires knowledge of music theory in order to run MIDI, while digital audio does not have this requirement.