nature of musical sound

Question 1

what is a sound?

Answer 1

longitudinal air pressure wave travelling outward from a sound source

Question 2

what is a period?

Answer 2

a periodic vibration in which the motion repeats itself exactly after a certain amount of time.

Question 3

what is the frequency (Hz)?

Answer 3

the number of periodic vibration cycles in one second.

Question 4

what is the formula for frequency?

Answer 4

f = 1/T

Question 5

what is the relationship (formula) between frequency (f), speed (c), and wavelength (λ)?

Answer 5

c = fλ

Question 6

what is amplitude and envelope?

Answer 6

• the amplitude of a vibration is the maximum displacement, measured from the point of equilibrium at rest
• the envelope is a smooth curve outlining the extrema of the vibration

Question 7

what is a phase?

Answer 7

a phase is when two vibrations are perfectly equal except for a shift in time. the shift is the phase.
it’s measured in radians.

Question 8

what is fourier’s theorem?

Answer 8

“any periodic vibration, however complex, can be decomposed into a sum of elementary sine waves”

Question 9

what is the difference between a pitched sound (tone) and an un-pitched sound (noise)?

Answer 9

• a tone is created by a periodic vibration. it has a discrete spectrum, including peaks.
• a noise is created by a vibration with no repeating pattern. it has a continuous spectrum (like white noise)

Question 10

what happens when two waves with the same frequency and amplitude meet?

Answer 10

• if they have the same phase, they add constructively and the amplitude is doubled.
• if the phase difference is half a period (or pi), they add destructively and the amplitude is brought to zero.

Question 11

what is the beating effect?

Answer 11

when two waves have close frequencies f1 and f2, they interfere both constructively and destructively at the beating frequency

fB = |f2 - f1|