Speech Science LEC 3

PGS 29-37

wavelength- λ

length of disturbance a wave creates in a medium in 2 consecutive identical points during 1 cycle, λ (distance from one point to another, peak to peak)

wavelength is dependent upon

frequency and speed of sound

λ= c/f (speed of sound/frequency)

wavelength is inversely related to _?

frequency

• low frequencies: have longer wavelengths, travel well through barriers (walls)

• high frequencies: have shorter wavelengths, tend to reflect off barriers

period vs wavelength

period is a cycle- time it takes for (0 to 0); wavelength is distance

• Wavelength (\(\lambda \)): The Wavelength is the spatial length between two identical points on a wave, such as peak to peak or trough to trough.

• Period (\(T\)): The period is the temporal duration required for a single wave cycle to pass a fixed point

Wavelength is the physical distance of one complete wave cycle, while period is the amount of time it takes to complete that cycle

where is psychoacoustics derived from?

psychoacoustics is derived from psychophysics

watts

watts- power

dynes

dynes-pressure

subsonic

too low frequency vibration to hear

ultrasonic

too high frequency to hear

human frequency range hearing threshold

20Hz-20KHz

Frequency

Hz

Pitch

Mels

2 things about pitch

1) ear is not equally sensitive to frequency changes at all frequencies (120Hz-220Hz is easy, 1000-1100Hz is difficult)

2) can percieve lower frequency (pitch) easier than higher

is pitch psychoacoustic or physical?

psychoacoustic, not measured only percieved

psychophysics

study of relationship between physical properties of stimulus and our subjective experience of the stimulus

psychoacoustics

study of sound perception

pitch

perceptual correlate of frequency; affected by intensity

loudness

perceptual correlate of intensity; affected by frequency

comprehension range for humans

100Hz-5000Hz

human vocal cords vibrate

80Hz-500Hz

is pitch and frequency is perceived as?

not linear; it stops being linear and turns logarithmic (ex: slide 8)

linear scale

scaling distance is equal, can sum units by addition eg: measuring stick 1+1=2

non-linear scale

scaling distance is not equal eg: log scale (multiplying)

frequency is a

measurable characteristic, physical

frequency + pitch are related in a non-linear way however

higher pitch results mostly from higher frequency, non-linear especially at freq >1000Hz

physical vs perceptual

Fo Pitch

Amplitude/intensity loudness

Duration length

what is amplitude

the extent of maximum air pressure variation from its “normal” position (amount of energy carried by a wave); the amplitude of sound waves corresponds to the amount of rarefaction and compression that occurs

greater amplitude=greater wave

greater amplitude is percieved as

increased loudness

intensity

energy(power) is the size of the local disturbance (compression/rarefaction of air molecule)

the greater the displacement of molecules, the greater the energy imparted to them

intensity= power per unit area (Watts/m²)

does amplitude capture how sound interacts with a medium?

amplitude does NOT capture how sound interacts with a medium like the air in a room as it travels for this we use intensity

intensity is related to power

is proportional to amplitude squared

intensity diminishes with increasing distance ex: distance up x2 intensity down x4, inverse relationship

small increases in sound pressure yield large increases in intensity

speech intensity is measured as

the relative power of one sound to another “_ in relation to _”

dB SPL

what is related to sound intensity?

amplitude of vibration

SPL

diff between the pressure of interest and the standard reference pressure expressed as a log; compare relative intensity of two sounds

dB SPL= 20 (log₁₀ P₀/P₁)

P₀ is sound to be measured

P₁ is reference sound

hearing sensitivity is

frequency dependent

JND (just noticable difference)

minimal difference between 2 sounds that can be percieved as having diff loudness levels

speed of sound in air (velocity)

psychoacoustic property

air a gas is slower than most media

is independent of sound pressure and particle velocity

dependent on the medium; varies a little with air conditions (temp) but is usually treated as a constant c = 344 m/s

speed of sound is not dependent upon

frequency or wavelength

speed of sound is determined by

1) density of the medium: (solid, liquid, gas) so helium transports sound wave faster than atmosphere

2) phase of the medium: tighter bonds of solids transmit sound energy faster than fluids so you can hear sound through a wall