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EPHE 341 > Signals > Flashcards

Signals Flashcards

1
Q

In biomechanics, we are dealing with values from sensors that have limitations based on…

A
  • Sampling
  • Sensor error
  • Environmental error
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2
Q

A signal has ____ that needs to be dealt with

A

noise

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3
Q

How can we deal with noise

A

By sampling properly
Smoothing data
Filtering data
Knowing some basics of signals and the transformations that we intend to perform on them

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4
Q

What is the Nyquist-Shannon Sampling theorem

A

In sampling an analog signal, the goal is to represent the original signal as accurately as possible with as few discrete points as possible. Sampling frequency must be a certain level in order to be accurately represented by discrete data

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5
Q

How do we ensure that sharp direction changes in the signal are not missed

A

Use sampling frequencies 5-10 times the Nyquist Frequency are often used

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6
Q

Do we deal with the noise before or after doing calculations

A

before

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7
Q

What are 3 smoothing techniques

A
  • Curve fitting
  • Polynomials
  • Splines
  • Moving averagea
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8
Q

What is curve fitting

A

Fitting a best-fitting function to the data

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9
Q

What is moving averages

A

Moving average over a window of samples gets rid of noisy spikes

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10
Q

What are 4 components to a signal

A

Frequency
Amplitude
Offset
Phase shift

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11
Q

What is frequency

A

The number of repeating cycles per unit time

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12
Q

What is amplitude

A

The magnitude of change

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13
Q

What is the offset

A

The distance of the mean amplitude from zero

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14
Q

What is the phase shift

A

A horizontal offset

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15
Q

Signals can be decomposed and reconstructed from…

A

a number of basic functions (sine waves)

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16
Q

Once can occur once a signal is decomposed

A

It can be represented in a frequency graph of the basic sine waves (frequency domain)

17
Q

What is frequency domain

A

A time-domain signal is converted to a frequency-domain signal with a mathematical technique called a Fourier Transform

18
Q

What is digital filtering

A

A way of reducing the frequency content of the signal so that it just obtains the signal you are interested in without the noise

19
Q

What is a common use of fourier transforms

A

To find the frequency components of a time domain signal that is mixed with noise

20
Q

Why can a filter be used to remove noise?

A

Noise is often of a different frequency than the intended signal

21
Q

What are 5 types of digital filtering

A 
low pass 
high pass 
band-pass 
band stop 
notch
22
Q

What is a problem with digital filtering

A

Phase distortion (usually phase-lags occur, shifts signal)

23
Q

What is the most common source of noise in human motion capture data

A

small errors in the position of the biomechanical markers during the digitization process

24
Q

Noise in motion capture data is usually…

A

Low amplitude and high frequency

25
Q

What is a low pass filter

A

A filter which multiplies everything above a certain point by 0 - Just interested in low frequencies

26
Q

What is a high pass filter

A

A filter which multiplies everything before a certain point by 0 - Just interested in high frequencies

27
Q

What type of filter most commonly used to smooth kinematic data

A

A low-pass filter

28
Q

What is the aim of filtering

A

Arrive at the highest signal : noise ratio

29
Q

When is noise in motion capture data amplified

A

each time the data are differentiated of integrated

30
Q

acceleration data arrived at by double-differentiating displacement data are typically smoothed using…

A

a low pass filter to increase the signal:noise ratio

31
Q

What is the highest voluntary frequency in human locomotion

A

Less than 30 Hz

EPHE 341 (17 decks)

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