Filters and Frequency Selectivity

Define filters

systems that are designed to modify the amplitudes of the frequency components of sounds

Define transfer function

a graph that shows you what happens to frequencies as they pass through a system

What is on the x and y axis of a transfer function?

x-axis: represents frequency

y-axis: represents magnitude

What is the purpose of a filter?

to let some frequencies pass or be attenuated/amplified

What are the main types of filters?

low-pass filter

high-pass filter

band pass filter

band stop/reject filter

Define low-pass filter

pass low frequencies and attenuate the high frequencies

Define high-pass filter

pass high frequencies and attenuate the low frequencies

Define band pass filter

passes frequencies in a specific range

Define band stop/reject filter

attenuates frequencies in a specific range

What characterizes a band pass filter?

center frequency (Fo, Fc) and bandwidth

Name the parameters of filters

center frequency

cut off frequency

bandwidth

slope

Name the two types of cut off frequencies

lower cut off frequency

higher cut off frequency

How do you find the bandwidth of a filter?

f(h) - f(l) = bandwidth

What is another name for slope?

roll off rate/attenuation rate

How do you calculate the slope of a filter?

by subtracting attenuation in dB between two frequencies one octave apart, in the region where the slope is steepest

Define quality factor

a measure of the frequency selectivity of a resonator or filter

Fill in the blank: the _____ the Q, the __________ the peak is and the more frequency specific a filter is

higher

narrower/sharper

How do you find the quality factor?

center frequency/bandwidth

Define frequency selectivity

the ability to separate different frequencies of sound

What is frequency selectivity important for?

sound discriminate and separate sounds that are presented together

Where does the frequency selectivity happen in the human auditory system?

basilar membrane

Fill in the blank: the cochlear traveling wave probably represents the ___________ cochlear function

passive

True or false: cochlear traveling wave has no sharp tuning

True!

Fill in the blank: the outer hair cells are involved in the _________ mechanism

“active”

What are OHCs important for?

sharp tuning and cochlear amplifier

Living OHCs are required in order to do what?

maintain the nonlinearity of the basilar membrane

Name the consequences of OHC dysfunction

reduced frequency selectivity

loss of hearing sensitivity

In basilar membrane traveling wave with OHC the wave travels?

wave travels from the base to apex

Fill in the blank: at peak of traveling wave, the displacement is greatest for _____ level sounds

low

True or false: the traveling wave quality factor are lower at low level inputs

false; higher at low level inputs

How is the tuning of a filter measured?

ISO-level procedure

ISO-response procedure

Name some aspects of iso-level procedure

response measured at one location

input level is fixed

frequency is varied

Name some aspects of iso-response procedure

response is measured at one location

output level is fixed

input level is varied

frequency is varied

What type of curve is this?

iso-level curve or physiological tuning curve

What type of curve is this?

iso-responsive/tuning curve

Physiological tuning curves indicates what?

frequency selectivity

Fill in the blank: in a physiological tuning curve, the quality factor __________ somewhat from low to high frequencies

increases

True or False: the sharper the peak of a tuning curve the higher the quality factor

true !

Name the characteristics of a healthy ear’s physiological tuning curve

high quality factor

BM tuning curves are sharp

Name the characteristics of a unhealthy ear’s physiological tuning curve

low quality factor

OHC loss

broadened tuning curve

elevated threshold of response