Advanced Analysis

Frequency-domain Analysis

Analyze time-waveform data in the frequency domain with the following advanced graphing functions:

• Fast Fourier Transform (FFT): Transforms time-domain data into the frequency domain.
• Power Spectral Density (PSD): Displays the power in a frequency band.
• Transfer Function: Signifies a resonance or antiresonance in a system.
• Coherence: Indicates how closely a pair of signals (x and y) are statistically related.
• Cross Spectral Density: Displays the power in a frequency band for a pair of signals that have been multiplied in the frequency domain.
• Transmissibility: Like transfer function estimates, signifies a resonance or antiresonance in a system.

Additional Traces

• Spectrogram: Displays the amplitude of multiple FFTs. What is a spectrogram?
• Nyquist: View transfer function data as a scatter plot. Used to assess the stability of a system with feedback during modal analysis.

FFT & PSD Analysis

Quick Tip Video

Understanding Waveform Relationships

Free VRU Course

Fast Fourier transform (FFT) and power spectral density (PSD) mathematics are powerful tools for analyzing the characteristics of a waveform. There are also several mathematic functions that help to explain the relationships between two or more waveforms.

The “Mathematics for Understanding Waveform Relationships” VRU course introduces three functions for comparing data: transfer function, correlation, and cross-spectral density.

Take the Course

Part number 1607

Resampling & Filtering

RESAMPLING: Adjust the sample rate of a time waveform

• Compare two data files with different sample rates
• Downsample data for quicker, more convenient handling if there is no high-frequency data
• Increase the smallest sample rate of the input files to increase the frequency resolution of an analysis algorithm like the fatigue damage spectrum (FDS)

FILTERING: Filter out, accept, or boost frequency components in a time waveform; options include high-pass, low-pass, and bandpass filters

• Filter out a DC offset or a frequency band contaminated by noise
• Remove frequencies outside a shaker’s specifications during file playback
• Filter to the transducer’s specifications to remove data outside its rated operation
• Attenuate rapidly-changing frequency components to smooth a noisy data sequence

Low-pass filter removing high-acceleration noise from high frequency data.

General Purpose FIR Filters

• Notch out one or multiple single-frequency components
• Filter out one or multiple bands of frequency components
• Add dips and bumps in the filter response to equalize
• Add a linear-phase filter

Advanced License

In addition to advanced analysis tools, the ObserVIEW Advanced license includes Multimedia Sync, Octave Analysis, and Math Traces.

Multimedia Sync opens a video file(s) and syncs it with the time of the recording. Then, view the video and data playback at the same and extract images/data for a report. You can also add other media files such as additional video files and audio files after the player is open. LEARN MORE.

Octave Analysis generates octave bands with an 8th-order filter to meet IEC 61260-1 Class 1 filter specifications. It performs filter-based analysis and can apply A and C frequency weighting, linear and exponential averaging, and peak hold. LEARN MORE.

Math Traces is a free entry field that builds a trace using existing trace data operated on by functions and operators.