To uncover the underlying causes of noise
, engineers depend on several essential analytical functions
to give them a clear picture of the system under testing including noise. Among these functions, some of the most common include:
Presentation over time, frequency, angle, or other quantities such as displacement, or rotational speed (tachometer)
Presentation in a color spectrogram as power-spectral-density (PSD)
Overall sound-level characteristic in dB(A)
Band-limited level characteristic in dB(A)
Analyzing a signal in frequency-domain does not show how the frequency content of a signal evolves over time
. For this task, features such as the spectrogram in catman®
provide the needed result. The spectrogram directly shows a Joint-Time-Frequency-Analysis (JTFA)
by computing the frequencies contained in a signal with the associated color-coded amplitudes over time. The catman® software uses the so-called Short Time Fourier Transform (STFT) to calculate the JTFA and applies a Fast Fourier Transform (FFT) repeatedly to short segments of a signal over time. In essence, the JTFA of a spectrogram shows more details than a standard FFT: frequency content (y-axis) over time evolution (x-axis), shown in a so-called 2-D 1/2 visualization where amplitude or energy is mapped to a color code.
The JTFA relies on parameters such as the number of measured values used to calculate the spectrum. The rule of thumb for these measurements is the more measured values you include in the FFT, the more accurate the resolution in the frequency range
. Another parameter is the window function
, which determines the weighting to be applied for sampling values derived from sampling a signal within a segment (window) when they are used in the calculation. If multiple channels are assigned to the graph, the spectra of the channels can also be displayed as the vector sum.
With the QuantumX / catman®AP measurement-and-analysis toolset, engineers can analyze all physical quantities of systems or products under investigation - including sound - whether for engineering, testing, production, or maintenance purposes.