PSD Analyzer Element

Summary ¶

	PSD Analyzer
Info
Category:	Signal Processing		AddIn:	Signal Processing
Creator:	OkazoLab		Scope:	Parent event
Owns Snippets:	None		Usage:	Snippets

Properties ¶

Name	Description	Constraints	Type	On runtime change
Signal Source
Selected Signal	Defines the signal for processing by the element. The signals are provided by the data acquisition elements.	Design Time..	Int32
Sampling Rate	Defines the sampling rate of the original signal, in Hz	Design Time..	Double
FFT Settings
Analysis Window Size	Defines the size (in samples) of the moving window for processing in this element.	Design Time..	Int32
Range Of Interest	Defines the 'range of interest' across all signal frequencies for analysis, such that the dominant frequency is searched within the range only. The range also restrains X-bounds on the generated plot.	Design Time..	clRange
Bin Size	Defines the bin size for the frequency dimension in statistics and plotting	Design Time..	Double
Power Normalization	Defines the normalization procedure applied to for estimated power values	Normal..	enPowe..
Fourier Options	Defines the computation options for the FFT	Normal..	Fourie..
Runtime Status
Is Running	Defines whether online processing and plotting is going on. You can turn off them at any runtime moment for a sake of performance.	Normal..	Boolean
Dominant ROI Frequency	Returns the dominant FFT frequency in the signal power spectrum within the range of interest, in Hz	Status..	Double
Dominant ROI Power	Returns the power of the dominant FFT frequency in the signal power spectrum within the range of interest, in Hz	Status..	Double
Dominant Binned Power	Returns the power of the dominant binned frequency in the signal power spectrum within the range of interest, in Hz	Status..	Double
ROI Bin Powers	Returns a double array containing freq. powers (grouped in bins) from the range of interest	Status..	Double..
XAML PSD Plot	Returns a live XAML control that can be used for direct binding to the Content property of the XAML ContentControl element, e.g. ContentControl with a generated staircase plot can be added to the status screen or to the XAML Layout element.	Normal..	UIElem..
Frequency Spectrum	Returns an double array of the instant frequency spectrum estimated by FFT. The length of the array is equal to the size of the analysis window. The spectrum is updated every Control Loop cycle of the parent event, if new signal samples are available.	Normal..	Double..
Plotting
PSD Plot Type	Defines the type of the PSD plot. The heatmap plot can be slower in rendering but it allows a signal overview over time	Design Time..	enPSDP..
Plot Title	Defines the title of the generated plot	Normal..	String
Plot Theme	Defines a visual theme of the generated plot	Normal..	Int32
Bar Color	Defines the color of power bars on the generated plot	Normal..	stColor
Bar Width	Defines the relative width of the bars on on the generated plot.	Normal..	Int32
Rendering Size	Defines the size of the generated plot in pixels. The plot is automatically stretched on rendering, but a larger rendering size improves the chart quality with some cost in performance. The rendering size is also used as the resulting image resolution, when the chart is saved into a file.	Design Time..	clSize
Font Size	Defines the font size for plot labels	Normal..	Double
Show Axis Bands	Defines whether the axis bands are shown on the plot area	Normal..	Boolean
Control
Is Enabled	If set to false the element is completely omitted when the experiment is run	Design Time..	Boolean
Title	Title of the element	Design Time..	String

¶

Description ¶

Snapshots ¶

Status Screen with the PSD plot, frequency statistics and selected powers

Practical Use ¶

Preparing the element for analysis ¶

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.
3. Add new PSD 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 the real sampling rate of the selected signal.
7. Choose the size of the analysis window via the corresponding property.
8. Select the Range Of Interest for statistics and plotting.
9. Define the bin size for the frequency dimension in statistics and plotting.
10. Choose the Power Normalization procedure (the default is normalization for the total signal maximum).
    

Creating the signal plot ¶

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

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

   
   

Reading the FFT results in code ¶

1. Create a proxy variable linked to the Frequency Spectrum 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:
   

   
   
   // estimating the spectrum sum
   
   double Sum=0;
   
   for (int i=0;i,FrequencySpectrum.Length;i++)
   
   {
   
   Sum=Sum+FrequencySpectrum[i];
   
   }
   
   

   
   

Notes ¶

• The Frequency Spectrum values are raw, so you may need to make a conversion to Hz based on the size of analysis window and sampling rate. In contrast, element's statistics and plot automatically scale the FFT results to Hz.
• The dominant frequency and power are searched only inside of the chosen range of interest.
• The frequency spectrum is returned for the entire analysis window, irrelative to the chosen range of interest.
• You can measure a time of one cycle of signal processing with the Control Loop Interval property on the parent event. With plotting on and off, the expected time for a 1000 sample window is ~10 and ~5 ms, correspondingly, given that there are no other processes in the parent event and in the experiment.
• If you are in time-critical section of your experiment, you can temporally cease the signal processing by setting the Is Running property to false.