Question 1

Which of the following best describes amplitude modulation (AM) when two sine waves of frequencies $$f_1$$ and $$f_2$$ are added together and $$f_1$$ and $$f_2$$ are close in value?

Accepted Answer

The resulting signal exhibits beats with a perceived frequency of $$(f_1$ + f_2$)/2$$ and amplitude modulation at a rate of $$|f_2$ - f_1$|.$$

Question 2

Given the amplitude modulated signal $$D(t) = A \cdot [1 + m \cdot \sin(2\pi F_m t)] \cdot \sin(2\pi F_c t)$$, what does $$F_c$$ represent?

Accepted Answer

$$F_c is $$the carrier frequency.

Question 3

A filter allows all frequencies below 500 Hz to pass through unchanged but attenuates frequencies above 500 Hz. What type of filter is this?

Accepted Answer

Low pass filter

Question 4

Which of the following is true about white noise?

Accepted Answer

White noise has equal power at all frequencies.

Question 5

If a filter has a low pass cutoff frequency $$f_{lp} = 200 Hz $$and a high pass cutoff frequency $$f_{hp} = 800 Hz$$, what is its bandwidth (BW)?

Accepted Answer

$$BW = 600 Hz$$

Question 6

A signal passes through a filter and its energy decreases by half at a certain frequency. What is the change in decibels ($$\Delta dB) at $$this cutoff frequency?

Accepted Answer

$$\Delta dB = -3.01 dB$$

Question 7

Which of the following is a property of a linear system?

Accepted Answer

The output to a sum of inputs equals the sum of the outputs to each input (superposition).

Question 8

A band pass filter has a roll-off rate of 12 dB/octave. What does this mean?

Accepted Answer

The filter attenuates frequencies by 12 dB for every doubling of frequency outside the passband.

Question 9

Which type of noise has more power at higher frequencies?

Accepted Answer

Blue noise

Question 10

A device is said to be nonlinear if:

Accepted Answer

Its output contains frequency components not present in the input signal.

Question 11

A bat uses frequency modulated (FM) calls for echolocation. Which of the following best describes an FM signal?

Accepted Answer

A signal whose frequency varies over time.

Question 12

Which of the following is NOT required to fully describe a filter?

Accepted Answer

The color of the filter's casing

Question 13

If you want to attenuate all frequencies between 1000 Hz and 2000 Hz but leave others unchanged, which filter should you use?

Accepted Answer

Band reject filter

Question 14

Which of the following best explains why sinusoids are used in psychophysics to study auditory systems?

Accepted Answer

Because the response to complex sounds can be predicted from the response to sinusoids in a linear system.

Question 15

A filter’s impulse response is measured by:

Accepted Answer

Applying a transient acoustic click and analyzing the output.

Question 16

Which of the following is a real-world example of a nonlinear device in audio systems?

Accepted Answer

A speaker that introduces distortion at high volumes.

Question 17

If the input to a linear system is doubled in amplitude, what happens to the output?

Accepted Answer

The output is doubled in amplitude.

Question 18

Which of the following statements about filters is correct?

Accepted Answer

Filters can selectively attenuate or pass certain frequencies in both simple and complex sounds.

Question 19

A narrowband filter with a steep roll-off rate is most likely to:

Accepted Answer

Have a long response time and ring after an impulse.

Mini-Textbook Study Notes: Modulation, Noise, Filters, and Linearity in Physics of Sound

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