week 4.2 Flashcards
discrete signal
X[k] the value of an analog signal at discrete points in tiem
every point in time of a discrete signal is determined by the…
sample interval (Ts)
t =
n*Ts = 1/ Fs
Fs
sampling frequency
1 / Ts
N
position of number in the sequence
analog vs digital
analog is continous while digital is interval based
continuous is amplitude vs time
discrete is amplitude based on sample number
sinosuidal
having sin wave
RMS defintion
calculates mean based on magnitude of numbers, not sign
ratio for comparing intensity of two signals
V signal one / V signal 2 (units dB)
comparing power of two signals
Pdb = 10log(p1/ p2)
comparing voltage of two signals (RMS)
p = v^2/R
SNR
signal to noise ratio
the ___ the SNR, the better the signal
larger
convert SNR to linear
10^ (SNRdb / 20)
if SNR is positive the signal is ___ than the noise
stronger
if SNR is negative, the signal is ___ than the noise
weaker
steps of biosignal measurement system
signal
sensor/transducer
signal processing
analog to digital converter
display/storage
post processing
analysis
interpretation
sensor/transducer
transduce biosignal to electrical one (still analog)
signal processing
process/condition signal to reduce noise and prepare for digitization
amplify, filter, shift
amplify signal
multiply by constant at every point in time or spae
filter signal
multiply by function in frequency domain
shift signal
add constant at every point in time or space
analog to digital converter
digitize by sampling continuous signal and discretizing the signal at each time/frq domain
choose the appropriate sampling rate
- fill input range of digitizer to max resolution
discretization
rounding to a number of finite precision
post processing
noise reduction with digital filters, averaging, FFT, down sampling
EMS recording system
device that connects electrodes to muscles and collects data when muscle is activated (ex: changing in length)
motor commands to muscle are transmitted through..
changes in electrical potential
EMS recording system records…
the difference in potential between two electrodes
sEMGs
have max amplitude of 5V, internal has 10V
*10V is better but you need to insert needle in patient which isn’t convenient
aliasing
when signal is discreetly sampled at an insufficient rate to capture changes in signal
i.e bad time intervals and inconsistent data
best approximation of signal is when…
you sample the signal multiple times per cycle
in aliasing, components of digitized signal at high frq are mistaken for..
components at low frequencies
how to avoid aliasing?
sample rate should be greater than or equal to twice the highest frequency present in the signal
Fs^3 = 2Fc
(Fs is sampling frq and Fc is highest frq in signal)
