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Page Revision: 2014/12/26 18:59

Test ¶

The element allows to read, analyze and plot a real-time signal that is provided by the signal acquisition elements in EventIDE.

Table of Contents [Hide/Show] Element' actions aligned with epochs of the parent event Properties     Generic Properties Test Description Snapshots Practical Use     Preparing the element     Creating the signal plot     Accessing the descriptive statistics of the signal samples     Reading the signal samples in code Notes

Description ¶

The signal acquisition elements, e.g. OpenViBE Signal, communicate with hardware and buffer incoming data samples at the background of the experiment. In order to access the buffered data, you can use Signal Analyzer. The element operates on a single signal and allows to read, analyze and plot the signal data. The analysis is performed cyclically in the control loop of the parent event. The analysis is done within the analysis window that embraces the selected number of recent samples. The analysis returns the descriptive statistics of the 'windowed' signal: mean, min, max and standard deviation. Other estimates should be done manually, hence the element allows reading the signal samples as array of double numbers. When signal monitoring is required, the element generates a live plot, which can be placed on the Status Screen (see the snapshot below).

Snapshots ¶

Snapshot 1

Practical Use ¶

Preparing the element ¶

1. Make sure that your experiment contains one of the data acquisition elements, e.g. OpenViBE Signal element
2. Prepare the data acquisition element such that it is set to collect at least one signal channel.
3. Add new Signal Analyzer element to the event, where you plan to process the signal (the element operates only within the parent event).
4. Select the added element to browse its properties in the Property panel.
5. Define a signal for processing, via the 'Selected Signal' property.
6. Adjust the 'Sampling Rate' property such that the value matches to a real sampling rate of the selected signal.
7. Choose the size of the analysis window via the corresponding property.
8. Select the 'signal normalization' procedure, if required.
9. If you want to filter the signal for plotting, turn on the bandpass filtering in the 'Bandpass Filter' group and adjust the filter parameter
   

Creating the signal plot ¶

1. Create a proxy variable linked to the 'XAML Signal Plot' property
2. Check the visual plot settings in the 'Plot Settings' group
3. Add a content control with data binding to the Status Screen code:
   

    
   
   <ContentControl Content='{Binding OnlineChart}'/>
   
   

   
   

Accessing the descriptive statistics of the signal samples ¶

1. Create proxy variables linked to the 'Mean','Maximum','Minimum' and 'Standard Deviation' properties of the element
2. If you want to access the statistics in code, use the Control Loop snippet of the parent event to monitor all signal updates:
   

   
   
   // Merging the statistics values into a string 
   
   string Statistics="Mean="+Mean+"\n Maximum="+Maximum+" \n Minimum="+Minimum+" \n SD="+StandardDeviation;
   
   

3. If you want to monitor statistics on the status screen at runtime, you can use the XAML textblocks bound to the proxy variables:
   

    
   
   <TextBlock Text='{Binding Mean,StringFormat=Signal Mean:      {0:F2}}' Foreground='Orange' FontFamily='Calibri' FontSize='16'/>
   
   

   
   

Reading the signal samples in code ¶

1. Create a proxy variable linked to the 'Signal Samples' property
2. Use the Control Loop snippet of the parent event to monitor all signal updates
3. Create a loop to read all signal samples
   

   
   
   // estimate the sum of the signal samples within the analysis window
   
   double Sum=0;
   
   for (int i=0;i,SignalSamples.Length;i++){
   
   Sum=Sum+SignalSamples[i];}  
   
   

   
   

Notes ¶

• The bandpass filtering affects only signal plotting, not the signal analysis.
• You can measure a time of one step of signal processing with the 'Control Loop Interval' property on the parent event. With plotting on and off, the expected time is ~10 and ~5 ms, correspondingly, given that there are no other processes in the parent event and in the experiment.