EEL6935: HW#2

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Due Thursday, July 27 at 5pm. Late homework will lose $e^{\char93 ~of~days~late} -1$ percentage points. Click on http://www.cnel.ufl.edu/analog/harris/latepoints.html to see the current late penalty. Answer the following questions with one or two sentences or a derivation. Don't write answers without explaining them.

1.

Auditory nerve fibers fire at some background spontaneous rate without any input. When a soft but audible tone is played, the fibers do not necessarily fire more often than their spontaneous rate. How then can we possibly differentiate between silence and when the soft tone is playing?

2.

What was Fletcher's major contribution to the auditory field?

3.

How does the nervous system likely achieve its 6 orders of magnitude sensitivity when individual neurons only have 3 orders of magnitude resolution (at best)?

4.

Why does the threshold of audibility increase when the stimulus duration decreases? Explain.

5.

What is the 3db point of a first-order low-pass filter $H(s)=1/(1+\tau s)$ (as a function of $\tau$)?

6.

What is the equivalent rectangular bandwidth of the above filter? Explain.

7.

Why do researchers use time-reversed signals in psychoacoustic experiments to determine time acuity?

8.

Which phonemes in speech are the most difficult to identify: vowels or consonants? Why?

9.

Three simultaneous tones are played at 450Hz, 750Hz, and 1050Hz. What pitch is perceived? Explain your reasoning.

10.

How do audiologists routinely check the hearing of newborn babies?

11.

Above a certain frequency the ITD cue for binaural localization breaks down. About what frequency does this occur?

12.

Why does ITD break down above this frequency?

13.

Below a certain frequency the IID cue for binaural localization breaks down. About what frequency does this occur?

14.

Why does IID break down below this frequency?

15.

How does the barn owl use IID different than humans do?

16.

Why do we have trouble localizing a pure 2KHz using HRTFs?

17.

Name a few cues we use to perceive the distance of a sound.

18.

When an echo is delayed longer than some crucial echo threshold time, the direct sound and the echo are heard as two distinct sounds. What is the approximate value of this echo threshold time?

19.

Describe a common situation where the precedence effect is not desirable.

20.

The engineering version of the cocktail party problem is typically posed as unraveling an instantaneous mixture of independent components with the number of measurements exactly equal to the number of components. List a few ways in which the biological solution to the cocktail party problem differs from the usual engineering version.