Biomedical Engineering Reference
In-Depth Information
When the desired signal repeats almost identically at each iteration, a form of block
averaging can solve the problem. In this case a sequence of points is sampled, covering
the duration and synchronized to the triggered event. This process is repeated a number
of times, as illustrated in Figure 5-58, and the sequences are avera
ge
d a number of times.
As
N
increases, the signal-to-noise ratio is improved by a factor
√
N
(in RMS value) until
the EP characteristics emerge from the random ECG background.
This averaging process can be described by
1
N
{
x
(
n
)
+
x
(
n
−
h
)
+
x
(
n
−
2
h
)
+
x
(
n
−
4
h
)
+···+
x
(
n
−
[
N
−
1]
h
)
}
(5.54)
y
(
n
)
=
FIGURE 5-58
Block averaging
process used to
extract evoked
potentials from
background EEG
activity. [Adapted
from (Bronzino
2006).]
