Multichannel Systems MC_Rack Manual - Manual (Page 149)

MC_Rack Features
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4.13.2 Detecting Spikes by a Threshold
You can define a threshold (spike detection level) for each channel separately. All peaks that
cross the threshold are detected. Spike traces are cut out around the detection event. The
resulting spike cutouts form a new data stream that can be further processed by other tools,
that is, sorted, analyzed, displayed, and so on. See also the preceding illustrations "Spike
detection" and "Voltage threshold not reached".
 If you select the option Negative Slope, the fall of the curve is regarded, otherwise the rise
is considered. This setting applies only to the selected channel. Under Apply to All, click Slope
to apply the slope setting to all channels.
There are several ways to set the detection levels. It is up to your choice which way you like to use.
 Select a channel from the drop-down list and define the threshold for this particular channel.
 You can change spike detection levels by moving them with your mouse in the display window.
The values in the rack window will then change automatically.
 You can then tune all channels, which means, that the different levels of all channels are
modified by the same factor (+ 1 μV or -1 μV).
 You can also apply the same detection level or the negative/positive slope to all channels.
Under Apply to All, click Level or Slope, respectively.
 The Automatic feature is very convenient to automatically assign an individual detection level
to each channel. The standard deviation of each data trace is used to estimate its spike threshold.
A time interval of 500 ms is used to calculate the standard deviation. You set the factor, by which
the standard deviation is multiplied. Click Refresh to calculate the standard deviation and apply
the result. It depends on the distribution of noise and spikes, which factor you should use. The
higher the spike rate, the lower the factor can be set. The sign of the factor determines whether
the spike detection level is positive or negative. You generally will use a negative factor. A value
between -1 and -4 is appropriate for most applications.
4.13.3 Detecting Spikes by Waveform
With this method, the shape of a signal is considered instead of the absolute height of a peak.
You define the minimum amplitude (in μV), and the minimum and maximum slope (in μV/μs)
that a signal must have to be considered as a spike. In contrast to the spike detection level, which
presents a fixed absolute voltage level, the Slope method searches the incoming data trace
continuously for a waveform that satisfies the following criteria: The slope range that is
specified by the minimum and maximum slope and the minimum amplitude (dV). The
preceding illustration "Spike detection" shows both methods of spike detection (for a negative
slope).
The amplitude parameter ensures that noise waveforms that satisfy the slope criteria, but has
a too small peak, are not detected (see illustration "Amplitude too small"). On the other hand,
there may be voltage drops that are high enough, but too slow or too fast, that is, the slope is
too low or too high, respectively. These are not detected, too (see illustrations "Slope too low"
and "Slope too high").