The spectrogram is a time-frequency diagram, also known as Waterfall diagram.
The X-axis of the spectrogram displays the time from left to right. The Y-axis shows audible frequencies from 10 Hz to 23 kHz.
The colors in the spectrogram represent the intensities of a frequency at a certain time. An intense color means a strong pressure of that frequency was recorded at that point in time.
The color mapping is customizable by selecting a different colormap preset, often blue represents low pressure, red is the highest recorded intensity.
The legend below the spectrogram shows the mapping of colors to values.
In the spectogram to the left we see a one second recording.
The horizontal red lines represent frequency bands that were present during the measurement.
A dotted line represents a pulsating signal that varied in intensity during the measurement.
Overall there is very little blue, which indicates that there has been noise in nearly each frequency.
Interpretation of the Spectrogram analysis
In the below example we see the relation of the spectogram to :
– spectrum (spectral analysis)
– far field image
In the example, a dry bearing creates a lot of noise, the Time Analysis shows the behavior.
In the spectral analysis we see which frequencies have been present during the whole measurement.
The most information is shown in the Spectrogram Analysis, there we see which intensities have occurred over time.
A useful aspect is that we can visualize these frequencies by selecting them and see their source in the Far Field Analysis.