Eclipse Additional Information Page 43
The effect of the High Pass Filter of the Amplifier
The high pass frequency you choose is the frequency above which frequencies are recorded. The number
next to the frequency indicates the filter slope in dB per octave. At the chosen frequency you will have 3dB
attenuation/filtering at the chosen frequency. All AEP high pass filters are analog Butterworth filters of 1
st
or-
der 6dB/octave or 2
nd
order - 12dB/octave. See below.
2. Preliminary display settings (visual smoothing)
Amplifiers for Evoked Potentials will always have a limited frequency response. This allows signal content
below a certain frequency to be disregarded. Certain tests will have certain desirable frequency limits. This
preliminary filter setting has no consequence for the data recorded, it only affect the visual presentation of
the recorded waveform. This may assist you during the editing function by eliminating unwanted noise from
recordings.
The High Pass Filter will reduce the low frequency content of a waveform (amplitude) - thus helping the vis-
ual inspection of the curves. Use of very heavy high pass filtering (e.g. 500Hz) will consequently greatly re-
duce the response amplitude.
The Low Pass Filter will reduce the high frequency content of a waveform (sharpness) - thus helping the
visual inspection of the curves. Use of very low pass filtering (e.g. 1000Hz) will consequently greatly reduce
the response sharpness (for some less distorted for others with missing details of the waveform). Using the
Low Pass Filter wil
l typically smooth the curve making it easier to pinpoint the peaks. Using heavy filtering
(e.g. 1000Hz) will often smooth the curve so much that it will be difficult to assign accurate markings to the
peaks. If you are looking only for wave V for fast screening situations, heavy filtering might be applicable.
The display filtering applied under Edit tab are all software digital filters, the Low Pass filters (6dB per oc-
tave). The High Pass filters are 33rd order filters.
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