SLHS 302 exam 1 Purdue

What is amplitude modulation (AM)

change in signal's amplitude over time

example of AM

SAM tones

What is frequency modulation (FM)?

change in signal's frequency over time

example of FM

chirps

safe levels of sound

below 90dB

when given the dB SPL at one distance, how do you calculate it for a second distance? ie. given: 80 dB at 5m, what is dB at 15 m

I2 = Iref + 20log(r1/r2)

what is periodic complex waves

wave repeats and is composed of multiple waves

example of periodic complex waves

vowels

what is an aperiodic signal

signals that don't repeat

exmaple of aperiodic

fricatives

what do time domains measure

amplitude and time

what do frequency domains measure

frequency OR level OR phase and amplitude

what does a spectrogram measure

amplitude and describes speech

Fourier's theorom

any complete wave can be described by the sum of its parts. can be used to analyze waveform into individual components

how to calculate RMS

RMS = A*0.707

describe the relationship between wavelength and period

direct relationship

describe the relationship between wavelength and amplitude

no relationship

define diffraction

the bending or spreading of waves when they encounter an obstacle

dependent on wavelength and sice

Mechanical

variation in position

Acoustic

variation in air pressure

Electrical

variation in voltage

peak amplitude

maximum positive displacement measure

instantaneous amplitude

displacement measure that varies with time

peak-to-peak amplitude

maximum total displacement

root-mean-squared amplitude

0.707 x Peak Amplitude for sinusoids

compute wavelength of sound wave with a period of 40 m/s, amplitude of 8 mm traveling through a medium with a speed propagation of 350 m/s. 0 degree starting phase

14 m

as frequency decreases, period ...

increases

as wavelength decreases, period ...

decreases

as frequency decreases, wavelength ...

increases

when frequency increases, amplitude ...

stays the same

sound level of 50 dB SPL, calculate the sound intensity in W/m^2

10^-7 W/m^2

sound level of 50 dB SPL, calculate the pressure in Pa

0.0063 Pa

calculate combined sound level for intensities: 80 dB + 80 dB

86 dB

calculate combined sound level for intensities: 80 dB + 85 dB

86.19 dB

amplify

get louder (add dB)

attenuate

get quieter (subtract dB)

pass

maintain signal

fundamental frequency

lowest frequency in a periodic symbol; highest common factor among harmonics

harmonics

spectral energy having a frequency that is an integer multiple of the fundamental frequency

octaves

doubling of the F0

standing wave

generated by the interaction of two sine waves of equal amplitude, traveling in opposite phases

sinusoids

basic sound and properties: describe sine waves

wave propagation

wave travels but stays in one position

particle motion

wave travels through medium, particles oscillate

amplitude

size of displacement

frequency

times per second (1/T), Hz

period

time to complete one cycle

vibration

anything with inertia and elasticity can vibrate

condensation

high density, high pressure

refraction

low density, low pressure

air pressure

function of force exerted on a given area

density

mass per unit volume

sound wave

alternation of condensation and refraction

wavelength

amount of distance covered in a single period

sound intensity

energy of propagation, wave is constant

when does sound intensity decrease

the further away the signal is from the medium

inverse square law

intensity is inversely related to the square distance for spherical waves

bel

logarithmic of a ratio of two intensity values

how much is a decimal is a bel

decibel is 0.1 of a bel

intensity reference value

10^-12 W/m^2

pressure reference value

2 x 10^-5 Pa

when doubling two of the same sound sources, how much do you add (ex. 70 dB + 70 dB)

+3 dB

absorption

energy taken in by object and converted, reducing sound

reflection

bouncing of sound waves off an object, redirecting energy back into space

contructive interference

2 waves add together

destructive interference

2 waves cancel each other out

- change sound pressure

size is relative to ...

wavelength

object > wavelength

high frequency, sound shadow occurs

object < wavelength

low frequency, diffraction occurs

reverberation

when sound is reflected, listener receives direct and reflected sounds

reverberation time

the time it takes for the reflections from a sound source to be reduced by 60 dB

node ends

fixed ends

antinode ends

free ends

complex sounds

waves comprised of more than 1 frequency

repeat time

how often a waveform repeats itself

amplitude spectrum

representation of the signal in terms of the sinusoidal components

2nd component of amplitude is reducedby 1/4,

waveform shape is affected, periodicity is not

1st component of amplitude is missing

shape is affected, periodicity is not, pitch is unaffected (be 100 Hz)

1st component of amplitude phase changed

shape is affected, periodicity is not

square wave

5ms period/repeat time means it has 200Hz f0, only odd harmonics are present, roll-off in amplitude if inverse of harmonic number (1, 1/3, 1/5, ...)

trianle wave

10ms period/repeat time means it has 100Hz f0, only odd harmonics are present, steeper roll-off because f0 fits so well (1/N^2) (1, 1/9, 1/25, ...)

modulations

change in amplitude and frequency over time

amplitude modulation

characterized by envelope and temporal fine structure

frequency modulation

characterized according to the range of frequencies over which signal changes

downward steep

frequency decreases

upward steep

frequency increases

alternating steep direction

down/up/down/up

long-term spectrum

spectrum of entire waveform over its complete duration

short-term spectrum

considers the spectrum at any point in time during stimulus duration

noise

aperiodic complex sound

white noise

all frequencies between specified limits are present and have the average intensity or power (N0)

bandwidth

defined by frequency limits and cutoff frequencies

total power (TP)

area of entire spectrum - dB

spectrum level (N0)

average intensity measured in a band of noise 1 Hz wide - dB/Hz

filters

change of amplitude spectrum of signal by some number of dB for each frequency component

amplitude response

ratio between amplitude of output and input for system as a function of frequency

low pass filter

pass low frequencies, attenuate high frequencies

high pass filters

pass high frequencies, attenuate low frequencies

band pass filter

pass range of frequencies, attenuate the end and beginning frequencies

band stop filter

pass range of frequencies, attenuate the middle values