Course Goals
Study the use of computers to create and analyze musical sounds
Study the use of computers to combine musical sounds into compositions
Study methods for computer storage and post-processing of music
Computer Sound Synthesis
Analysis of musical sound
Fourier analysis and transforms
Filtering and windowing
The phase vocoder algorithm
Synthesis of musical sound
Additive synthesis
Subtractive synthesis
Nonlinear synthesis
Computer Music Synthesis
Generation of music using computers
Direct transcription
Stochastic (random) algorithms
Artificial intelligence algorithms
Post-processing and storage of music using computers
Reverberation and localization
MIDI
Popular sound file formats
Interdisciplinary Nature of Computer Music
Music (composition and performance)
Computer Science (programming and algorithms)
Electrical Engineering (digital signal processing)
Physics (acoustics)
Psychology (cognition theory)
Principles of Sound
Sound is the perception we sense when the components of a medium (e.g. air) are subject to a vibration that is detected by the inner components of the ear.
Sound waves are the vibrations that travel through the medium.
The frequency f of a (periodic) sound is the number of cycles that pass the point per unit time. (Hertz = cycles/second)
The period T of a (periodic) sound is the time it takes for one cycle to pass a given point. Thus, T = 1/f.
The amplitude A of a sound wave in air is the amount the pressure changes (maximally) from atmospheric pressure.
The intensity I of a sound wave is a measure of its power, measured in decibels.
Physical sound intensity is usually measured in decibels above the "threshold of hearing" at 1000 Hz (Iref = 10-12 watt/m2)
IL = 10 log10(I/Iref)
Intesity level can be measured from any reference.
Examples:
Rock band (10 watt/m2). Find IL.
Answer: IL = 130 dB.
Quiet home (30 dB). Find I.
Answer: I = 10-9 watt/m2
Doubling the intensity of a sound corresponds to an increase of how many decibels?
Answer: +3 dB
Fletcher-Munson Curves [HANDOUT]
Types of Musical Sounds
Strings (violin, guitar, banjo)
Wind (flute, tuba, trumpet)
Percussion (drums, piano, xylophone)
Voice
Other Sound Properties
Sound intensity is affected by the type of medium and the distance travelled.
The velocity of a sound wave is affected by the temperature of the medium.
The direction of a sound wave is affected by the properties of surfaces in the path of the sound wave.
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