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Return to Research Methods Using R 1e Student Resources
Chapter 10 Multiple choice questions
Quiz Content
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not completed
.
Download the data file for the multiple-choice questions for Chapter 10,
and open it in
R.
The file contains two vectors called
HBwaveform
and
HBenvelope
. They are from a 10-second audio recording of a fetal heartbeat, sampled at 44100Hz. Plot the waveform as a line plot and count the beats (note that there is some high frequency noise, but the beats are clear as bursts of activity). How many heartbeats are present?
9
correct
incorrect
11
correct
incorrect
15
correct
incorrect
20
correct
incorrect
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not completed
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Calculate the Fourier transform of
Hbenvelope
, and plot the amplitude spectrum from 0-5Hz. Note that the sample is 10 seconds long. Aside from the DC component (at 0Hz), which frequency produces the largest amplitude?
0.5Hz
correct
incorrect
1Hz
correct
incorrect
1.1Hz
correct
incorrect
2.1Hz
correct
incorrect
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In the Fourier transform of the envelope, implement a crude low-pass filter by setting the amplitude of all frequencies above 5Hz to zero, then take the inverse transform. Do the same for the waveform. Plot both of the filtered signals. What do you observe?
The envelope still has clear peaks for each heartbeat, but the waveform does not.
correct
incorrect
The waveform still has clear peaks for each heartbeat, but the envelope does not.
correct
incorrect
The signals are smoothed, and both still have visible heartbeats.
correct
incorrect
Neither signal has a visible heartbeat.
correct
incorrect
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At the sample rate of 44100Hz, what is the Nyquist limit (the highest frequency we can represent)?
441000Hz
correct
incorrect
0.1Hz
correct
incorrect
44100Hz
correct
incorrect
22050Hz
correct
incorrect
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If we had a longer sample with a duration of 20 seconds, that was sampled at 260Hz, what would the frequency resolution of the Fourier spectrum be?
0.1Hz
correct
incorrect
0.2Hz
correct
incorrect
0.05Hz
correct
incorrect
20Hz
correct
incorrect
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The vector
filter1
contains a filter in the temporal domain. Take the Fourier transform of the filter and plot the spectrum. The filter is:
A low pass filter
correct
incorrect
A bandpass filter
correct
incorrect
A high pass filter
correct
incorrect
A notch filter targeting a single frequency
correct
incorrect
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The matrix
spatfilt
contains the Fourier spectrum of a spatial filter. Plot the filter using the
rasterImage
function:
plot(x=NULL,y=NULL,xlim=c(0,1),ylim=c(0,1),axes=FALSE, ann=FALSE, lwd=2
)
rasterImage(spatfilt,0,0,1,1
)
What can you deduce about its characteristics?
It allows through vertical information in a restricted frequency range
correct
incorrect
It allows through vertical information of all frequencies
correct
incorrect
It allows through horizontal information in a restricted frequency range
correct
incorrect
It allows through horizontal information of all frequencies
correct
incorrect
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not completed
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The matrix
ampspec
contains the Fourier amplitude spectrum of an image. Based on the knowledge that the lowest spatial frequencies have the highest amplitudes in most images, where are these represented in this spectrum?
In the centre of the spectrum (i.e. the spectrum has been quadrant shifted)
correct
incorrect
In the corners of the spectrum (i.e. the spectrum has not been quadrant shifted)
correct
incorrect
At random around the spectrum
correct
incorrect
It depends on the phase spectrum, which has been removed
correct
incorrect
*
not completed
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The matrix
filteredim
contains an image that has been filtered. Display it using the
rasterImage
function. What sort of filter has been used?
A low pass filter
correct
incorrect
A high pass filter
correct
incorrect
A horizontally oriented filter
correct
incorrect
An obliquely (diagonally) oriented filter
correct
incorrect
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The matrix
imspec
contains the Fourier spectrum of a greyscale image. Note that the quadrants have not been shifted, so the lowest frequencies appear in the corners. Take the inverse transform of the matrix and display it as an image (you will need to scale the luminances between 0 and 1). What does it show?
A chicken
correct
incorrect
A rainbow
correct
incorrect
A mushroom
correct
incorrect
A cat
correct
incorrect
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