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exam 2 Flashcards

1
Q

Rapidly changin signals have relatively ____

A

high frequency content

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2
Q

Slowly changing signals have relatively ____

A

low frequency content

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3
Q

Why is it important to determine the frequency content of a biomedical signal?

A

it provides quantitative information about signal morphology and periodictiy

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4
Q

What can you make out of knowing the bandwith of a signal?

A

you can convert a signal from analog to digital, design instrumentation and digital filters to have faithful detection and separate signal from noise to increase a SNR

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5
Q

How do you determine the frequency bandwidth or spectrum of a signal?

A

You utilize fourier analysis

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6
Q

What are the types of fourier analysis?

A

fourier series, discrete fourier series, fourier transform, and discrete fourier transform (DFT/FFT)

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7
Q

What is the relation between fourier and laplace?

A

Fourier transform is a special case of laplace transform

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8
Q

What do you use to determine the output of a continuous system?

A

Laplace Transform

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9
Q

What do you use to determine the output of a continuous signal?

A

Fourier Series

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10
Q

What do you use to determine the output of a discrete system?

A

Z-transform

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11
Q

What do you use to determine the output of a discrete signal?

A

DFS if its periodic and DFT is its not

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12
Q

What kind of signal is a biomedical signal?

A

Deterministic with a random component

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13
Q

What kind of signal is a biomedical signal usually?

A

a digital signal with finite duration

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14
Q

What do you use to process biomedical signals?

A

DFT or FFT

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15
Q

What question does a fourier series ask?

A

Given a continuous perioidic signal, how do you find its trigonometric-series representation?

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16
Q

Whats the answer to the question a fourier series asks?

A

an analog perioidc signal can be represented as the infiitne sum of sines and cosines with frequencies that are an integer multlple of the signal fundamental frequency = 1/period

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17
Q

How do we determine the values of the coefficients (weights) ao,a1,a2,b1,b2 etc?

A

equations given, ao is the average value of the waveform over one period

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18
Q

What can be used to plot the frequency spectrum of the signal?

A

the coefficients an and bn

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19
Q

are rhythm and frequency content the same?

A

no

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20
Q

what question does autocorrelation address?

A

Is the signal’s present value correlated with its past values? Does the signal contain a possibly hidden oscillation or rhythm?

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21
Q

what is the most common use for an autocorrelation function?

A

to find perioicities in a signal, it evaluates how well a signal corealters with itself at vatious time lags, hence attempts to locate the dominant periodic element (rhythm) within a signal

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22
Q

when does a correaltion function become autocorrelation?

A

when two signals are the same

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23
Q

what is usually chosen as the estimate for cycle length in a perioidc pattern in a signal?

A

the non zero delay that results in the next largest peak

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24
Q

what is rxy determined by?

A

the shapes of x[n] and y[n]

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25
what is the most common use of a cross correlation function?
to determine whether x[n] and y[n] contain periodic components of the same frequency (joint periodicity).
26
What does the graph of a first derviative signal indicate?
first derivative of a signal indicates its rate of change at any given point, essentially telling you where the signal is increasing or decreasing
27
what does the graph of a second derivative signal indicate?
the second derivative reveals the curvature of the signal, signifying whether it is concave up or concave down at a particular point; essentially, the second derivative shows how the rate of change itself is changing
28
What type of fourier analysis is to be used on a strictly deterministic signal?
fourier series, dfs, continous fourier transform, and dft
29
what kind of fourier analysis do random signals take?
DFT or FFT
30
How do you calculate periodic rhythm?
1/T(0)
31
what is the nyquist frequency?
it is fmax = fs/2
32
Where is all the frquency information in X[n] contained in DFT?
in the first N/2 complex coefficients of X[k]
33
What determines the resolution of the amplitude frequency spectrum for a digital signal?
the duration of the signal, so as the period is increased, the spectral resolution does too
34
Does the resolution of a resulting DFT spectrum rely on sampling frequency as long as the nyquist criterion is met?
no
35
what is an aliasing error?
it is when high frequencies are presented as low frequencies and there is a general loss of information and high frequency components
36
How do you findth frequencies for the Ni/2 harmonics?
multiply K by the fundamental frequency = fs/Ni (changes frequency to Hz on the x-axis)
37
Nyquist Criterion
exact reconstruction of an analog signal from its samples is possible if the signal is bandlimited and the sampling frequency is greater than twice the signal bandwidth
38
what is the cutoff frequency for an antialiasing filter?
its set at 70-80% of the maximum frequency that is wanting to be preserved in the digital signal
39
analog low pass filters _____ have _____ sharp roll off
do not have infinitely sharp roll off
40
Describe superposition in terms of an LTI
if two separate functions were put into a discrete system and receive two separate outputs, then it can be assumed that the sum of the two inputs will result in the sum of the two outputs
41
Describe time shift in an LTI
A time shift or delay of the input sequence causes a shift in the output sequence as well
42
What's an LTI?
Any system that is a set of linear, constant coefficient differential equations (continuous) or difference equations (discrete)
43
What is an LTI system completely characterized by?
its impulse response function, h(n)
44
If you know a system's h(n) then you can compute ____ by convultion
the system output for any input by convolving h(n) and x(n)
45
in knowing the impulse response function h(n) how do you calculate the frequency response function or transfer function?
FFT(h([n])
46
what is the impulse response of an LTI system
the time domain signal which appears at the output of the system when an impulse function is applied to its input
47
how do you find h[n]
by sending an impulse function as the input and observing the output of the signal
48
what is the output of a digital LTI system?
it is the convolution summation of h[n] and system input
49
What is the main objective o the A/D conversion process?
convert the analog signal to a digital signal with a minimum loss of information
50
what are two important aspects of data acquisition for A/D conversion?
sampling rate (nyquist) and the type of A/D converter
51
What is the goal of the amplification step of A/D conversion
it brings the amplitude of the signal into the range of the A/D converter (maximizes A/D conversion resolution)
52
What is the goal of the Analog low pass filter (anti-aliasing filter) step of A/D conversion
it bandlimits the analog signal
53
what is the importance of band limiting a signal
it helps to decide the proper sampling frequency based on the nyquist criterion to avoid aliasing
54
what is the upper limit on sampling frequency set by
the time needed for the a/d conversion process
55
What is the goal of the sample and hold circuit step of A/D conversion
it samples the filtered analog signal as nearly instantaneous as possible and, holds the sampled value constant during the subsequent A/D conversion process
56
What is the goal of the A/D conversion step of A/D conversion
it changes the analog voltage values stored by the sample and hold circuit to a digital represenation
57
What two things occur during the A/D converter step of A/D conversion?
quantization and encoding
58
what is quantization in terms of A/D conversion?
assigning the sampled signal values to discrete amplitude levels (quantization levels)
59
what is encoding in terms of A/D conversion?
taking the quantized samples (decimals) into binary format
60
what determines the quantization resolution in A/D conversion?
the number of bits
61
Describe quantization error in A/D conversion?
There will always be some quantization error because the magnitude of each sample must be expressed by some fixed number of digits
62
what determines the amplitude resolution of the A/D converter
q = full scale range/2^N
63
Describe an analog filter
it uses electronic components such as resistors, capacitors, amplifiers, etc
64
describe a digital filter
A digital filter consists of a mathematical operation
65
How do you determine the order of a digital filter?
which ever number is higher between N and M
66
What are the two major types of digital filters?
finite impulse response (FIR) and infinite impulse response (IIR)
67
What does the FIR depend on
depends on only current and past inputs and no feedback (x) and x(n-1)
68
what are the advantages of FIR filters?
stable beacuse the output is bounded for every input that is bounded and has linear phase
69
what does it mean to have linear phase
it means that phase distortion is minimized; all of the frequency components are delayed the same- distortion occurs when this isn't the case
70
what is the disadvantage to an FIR filter?
it can be difficult to synthesize
71
What is an example of a FIR filter
notch filter, high pass filter
72
describe an IIR filter
it is a recursive and infintite filter
73
what does it mean that an IIR filter is recursive
its output depends on the input and previously filtered values (feedback)
74
what is an example of an IIR filter?
trapezoidal integration
75
what is an advantage to IIR filters?
sharp roll offs, computationally simpler than FIR filters
76
what is a disadvantage to an IIR filter?
it can be unstable due to feedback and can usually have a nonlinear phase which causes phase issues
77
what is the advantage to convolution in frequency domain
no analytical expression required for the filter frequency response function
78
what is the disadvantage to convolution in frequnecy domain
implementation is complex and time consuming
79
what is the cutoff frequency in a low pass filter
the highest passband frequency
80
what is the cutoff frequency in a highpass filter
the lowest passband frequency
81
describe the bandwidth of a filter
passband's frequency width
82
whats the bandwidth of a low pass filter
the cutoff frequency or the frequency where the amplitude is 70% of the maximum amplitude
83
how do you determine the curoff frequency of a high pass filter?
you decide if its a FIR or IIR, calculate h(n) which you transform with discrete fourier transform, determine what the frequency is at 70.7% of the max amplitude
84
what is coherent averaging
removing repetitive noise without losing signal info
85
how do you determine coherent average?
by aligning multiple measured events with respect to some time marker and average the corresponding data points
86
What assumptions must be made for coherent averaging?
noise must be random, the time components must be accurately known, the signal must be repetitive in its morphology
87
what is the advantage to coherent averaging?
it improves the signal to noise ratio by a factor of sqrt(m)
88
Under what conditions would you consider using coherent averaging instead of filtering to remove noise/artifacts from signals?
when there is significant overlap between the constant signal and random noise because filtering would attenuate the constant signal as well as the noise

computer applications for BME (1 decks)

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