- NB: Document written for OpenViBE 2.2.0 (last update 22.Nov.2018)
This page provides instructions for using the Simulated Deviator driver in the OpenViBE Acquisition Server. The driver appeared the first time in OV 2.2.0.
Simulated Deviator is a data generator whose purpose is to misbehave. This can be used to test how the Acquisition Server and the signal processing (DSP) pipelines in Designer would react to various kinds of acquisition hardware anomalies. Hence the Simulated Deviator attempts to mimic such bad behaviors as some EEG amplifiers might occasionally do.
Simulated Deviator sends out 3 channels: The signal, the true sampling frequency, and the amount of drift. Currently it models two kinds of anomalies: the sampling rate not being what it was declared to be by the device, and freezes.
You can configure the badness of the Deviators’ behavior with the following settings:
- SendPeriodicStimulations. Does the driver repeatedly send a stimulation?
- Offset. How much the actual sampling frequency is ‘off’ from the one that the ‘device’ declares to the Acquisition Server? In Hz. Can be negative.
- Spread. The actual sampling frequency is a random walk that changes by additive steps drawn from a Gaussian distribution. Spread is its variance.
- MaxDev. The actual sampling frequency will stay capped to ‘declared rate +/- maxDev’.
- Pullback. This is the strength that the deviating sampling frequency gets tugged towards the declared sampling rate.
- Update. How often is the actual sampling frequency updated? In seconds.
- Wavetype. Sine or square signal.
- FreezeFrequency. How often does the driver freeze on average (Poisson process)? I.e. when its frozen, it doesn’t return any samples. In hz.
- FreezeDuration. When the driver freezes, how long does it stay frozen? In seconds.
It would make sense to rework Simulated Deviator into an Acquisition Server plugin, so that it could add anomalies to outputs of real EEG devices, or to operate after Fiddler, the P300 debugging tool.