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Table of Contents
Metric Compute Power From DFT Coefficients
The power in a signal can be computed from the DFT coefficients.
The form of the DFT is as follows:
p(t)= p0 + p1 sin(w t) + p2 cos(w t) + p3 sin(2w t) + p4 cos(2 w t) + ….
where w = 2 * PI * Base_Frequency
the power at a given frequency is given as the sum of the squares of the coefficients.
For example, the power at the Base_Frequency is given by (p1^2 + p2^2) the power at 2 * Base_Frequency is given by (p3^2 + p3^2)
This can be useful when looking at muscle related signals like EMGs.
Pipeline Command
The command below is as seen on the Visual3D application, it can be found in the Pipeline Workshop within the Metric folder.
Metric_Compute_Power_From_DFT_Coefficients /SIGNAL_TYPES= ! /SIGNAL_FOLDER=DFT ! /SIGNAL_NAMES= ! /RESULT_FOLDER=DFT ! /RESULT_SUFFIX=_POWER ;
Additionally (starting in Visual3D Version 5) the Mean and Median Frequency are computed.
These two metrics are commonly used to describe changes related to muscle fatigue.
Command Parameters
- Table with parameters and descriptions (include link to parameter wiki pages if they are available)
The following table shows the command parameters and descriptions:
| SIGNAL_TYPES | Specify Signal Types |
| SIGNAL_FOLDER | Specify folder containing signals |
| SIGNAL_NAMES | Specify names of signals to be processed |
| RESULT_FOLDER | Specify destination folder for results |
| RESULT_SUFFIX | Specify suffix attached to resulting signals |
Examples
Simple example
Complex example
Signal Components
The resulting Metric signal has two components.
The first component is the frequency. The second component is the power at the associated frequency.
Median Frequency
The Median Frequency is the Frequency at which the Integral of the Power Spectrum to that Frequency equals half the Integral of the Total Power Spectrum (e.g. divides the power spectrum in two)
where MF = Median Frequency
Mean Frequency
The Mean Frequency is the Ratio of the Integral of the Frequency*Power over the Integral of the Power.
_STATS
An additional result signal appended with _STATS is also created.
This signal contains the median frequency (component 1) and mean frequency (component 2)