Chapter 21 Musical Sounds
1. NOISE VERSUS MUSIC Wham - Noise and Wave Forms Three characteristics of a musical tone: Pitch Loudness Quality
2. PITCH • The pitch of a sound relates to its frequency. • The exact relationship is complex. • For simple sounds, the greater the frequency the greater the pitch. • For complex sounds, pitch assignment is an involved psychological process.
Change pitch by altering the vibrating source. • Response to high pitch usually declines with age.
3. SOUND INTENSITY AND LOUDNESS • Intensity - refers to pressure variations • Intensity is directly proportional to the pressure amplitude squared. • The human ear can hear intensities over a tremendously large range. • Loudness depends on intensity in a complicated way. It does not increase as rapidly as intensity.
Loudness • b = 10 log(I/Io) • Measured in decibels (db) • A difference of 10 dB corresponds to a ratio of intensities of 10X. • Loudness depends on our sensitivity to different frequencies.
4. QUALITY • Quality is the same thing as timbre. • It is easy to distinguish two different instruments playing the same note. • The quality of a musical sound depends on the number of partial tones and their relative intensities.
Harmonics and Overtones • The lowest frequency associated with a musical note is called the fundamental frequency. • Any partial that is a whole number multiple of the fundamental frequency is called a harmonic. • Overtones are consecutively numbered partials of frequency higher than the fundamental.
1st 2nd Sum Adding Harmonics
Demo - Harmonics on a Guitar • Demo - Organ Pipe
Speaker Shortcomings • The brain can fill in missing lower harmonics that small speakers cannot create.
5. MUSICAL INSTRUMENTS • Three basic types • stringed, air column, and percussion • Because of energy loss, string sections in orchestras are generally larger. • Electronic
6. FOURIER ANALYSIS • The eardrum responds to a sum of all the waves arriving at a particular instant. Yet the individual sounds are “heard.” • Any waveform is composed of an infinite number of simple sine waves of various frequencies and amplitudes.
Adding Harmonics Spreadsheet
7. COMPACT DISCS • Phonograph players give analog signals. • Digital signal is in binary code. • CD has flats and pits and is sampled 44,100 times per second.
Diatonic C Major Scale Letter Frequency Frequency Note Name (Hz) ratio Interval do C 264 9/8 Whole re D 297 10/9 Whole mi E 330 16/15 Half fa F 352 9/8 Whole sol G 396 10/9 Whole la A 440 9/8 Whole ti B 495 16/15 Half do C 528
The quality of a musical note can be changed by simply playing the note on a different instrument. (a) True (b) False (a) True
If the note middle C has a pitch of 262 vibrations per second, its second overtone on a vibrating string has a frequency of (a) 131 vibrations per second (b) 262 vibrations per second (c) 524 vibrations per second (d) 786 vibrations per second (e) none of the above (d) 786 vibrations per second
The three characteristics of a musical tone are loudness, quality, and timbre. (a) True (b) False (b) False
The wavelength of the fundamental vibration on a l m long string is half as long as the wavelength of the fundamental vibration in a closed organ pipe of l m length. (a) True (b) False (a) True
The ear can “Fourier analyze” a sound wave, but the eye cannot “Fourier analyze” a light wave. (a) True (b) False (a) True
If the fundamental frequency of a violin string is 440 Hz, what is the frequency in Hz of the first overtone? (a) 1320 (b) 880 (c) 440 (b) 880