FFT Analysis

The program FFT (Fast Fourier Transform) Analysis is used for narrow-band spectral processing of signals coming from the input channels of ADC modules and FFT spectrum analyzers (in real-time or recorded time realization view mode), as well as for viewing various spectral characteristics of signals.

Spectral analysis is used for dividing signals into basic constituents in the frequency area. This analysis is based on signal time realization decomposition into the frequency spectrum with an even frequency increment by means of Fourier transform.

Using the Narrowband spectrum program, based on the spectrum shape, the user can determine the presence of any signal tones (discrete constituents) and noise components in the measuring channel. Additional options of spectrogram building (in a 2- and 3-dimensional view) enable tracking of the non-stationary processes dynamics. A spectrogram is a spectral time representation of a signal, calculated for even time intervals. Building spectrogram sections based on time and frequency enables control of the non-stationary processes parameters.

Narrow-band spectrum - formula 1

Narrow-band-spectrum-Metallica-1-Spectrogram

Narrow-band-spectrum-Settings-window

Narrow-band spectrum - graph display options

The possibility to obtain the maximum and averaged spectra values and to compare them with their pre-set spectra (norm) enables evaluation of the difference between the pre-set and actual spectrum level. This option is necessary for various types of equipment monitoring, input/output control.

Simultaneous spectral analysis in various frequency bands of one and the same signal allows to observe the spectrum both in the entire frequency band (panoramic mode) and a detailed spectral analysis in the selected frequency bands. It is necessary if the signal has several high or low-frequency discrete constituents.

High-frequency resolution (up to 32,000 bands) allows to accurately determine the frequency of a stationary signal tone and to divide several adjacent frequency components. Such situation often occurs during vibroacoustic analysis of various mechanisms with electric drive. In the range about 50 Hz, several discrete constituents are typically determined, which are related to the electromagnetic blast, mechanical oscillations caused by the rotation of an asynchronous engine. All of these sources are typically located in a band of up to 0.5 Hz.

When analyzing noise components, discrete constituents on the spectrum could be quite disturbing. The program provides an option Clearing spectrum from discrete constituents (DC). This function suppresses all stationary signal tones.

Piezoelectric accelerometers are usually used for vibroacoustic analysis. These sensors send a signal proportional to the acceleration at the attachment point. Norms for vibration levels and their spectral composition are usually determined by the vibrational velocity value. To obtain a vibrational velocity signal, it is necessary to integrate the vibrational acceleration signal based on the time. For balancing, it is necessary to obtain the vibrational displacement value at the sensor attachment point. A vibrational signal time-based double integral allows for obtaining a vibrational displacement signal. These additional signal integration and differentiation functions are available in the described program.

For measuring the discrete constituents level, the root-mean-square (RMS) is usually measured in the filter band. In this case, the level of the discrete constituent does not really change against the analysis band. For measuring the level of noise components, it is necessary to measure the spectral power density (SPD) which is set in unit of measurement/√Hz. This is necessary because the noise spectral power density does not depend on the analysis band. FFT Analysis allows to calculate the spectra based on RMS, SPD, and amplitude values.

The user can also configure the representation parameters of the Narrow-band spectrum program in accordance with his requirements. In order to activate the graph display parameters window, right-click the graph area.

The user can configure the following parameters:

  • vertical and horizontal scale  (uniform, logarithmic, decibel, /1/n octave);
  • grid settings;
  • setting display parameters— type of lines, graph color, thickness of graph lines, etc.;
  • grid color and fonts settings;
  • adding hint windows — a comment to a particular graph point.

Main Features

  • signal level measurement in narrow spectral bands. The number of bands can be equal to the power of 2 (64, 128, 256, 512, 1024, 2048, …, 32768) or to an arbitrary integer number (50, 100, 200, 500, …, 50 000);
  • spectral analysis dynamic range: 170 dB;
  • averaging of the analyzed signal: from 0,01 up to 1000 seconds;
  • averaging types: linear, exponential;
  • implementation of weighting functions: rectangular, Hann, Hamming, Blackmann, Bartlett;
  • signal integration/ differentiation;
  • signal processing based on particular algorithms: fast (FFT) and discrete (DFT) Fourier transform;
  • type of the analyzed signal representation: spectral density, spectral power, RMS or amplitude value;
  • implementation of median filter for elimination of spectrum discrete components.
  • calculation and display of signal cepstrum (reverse Fourier transform);
  • calculation and display of the transient characteristics;
  • calculation and display of spectral graphs in 2-dimensional format (with color indication of signal level) and in 3-dimensional format;
  • calculation and display of maximum and averaged values for a set period of time;
  • graphs overlay option for transient processes analysis;
  • harmonic components analysis;
  • recording and reproduction of program configuration for the repeated measurement processes;
  • integrated correction function for the FR characteristics.

Analysis frequency range of the program Narrow-band spectrum for  FFT spectrum analyzers ZET 017-U

Sampling frequency
f, Hz
Range, Hz
Frequency resolution, Hz
50 000 0…20 000 0…2 000 0…200 0…20 0…2
from 0,5 up to 500 from 0,05 up to 50 from 0,005 up to 5 from 0,0005 up to 0,5 from 0,00005 up to 0,25
25 000 0…10 000 0…1 000 0…100 0…10 0…1
from 0,25 up to 250 from 0,025 up to 25 from 0,0025 up to 2,5 from 0,00025 up to 0,25 from 0,000025 up to 0,025
5 000 0…2 000 0…200 0…20 0…2 0…0,2
from 0,05 up to 50 from 0,005 up to 5 from 0,0005 up to 0,5 from 0,00005 up to 0,05 from 0,000005 up to 0,005
2 500 0…1000 0…100 0…10 0…1 0…0,1
from 0,25 up to 25 from 0,025 up to 2,5 from 0,0025 up to 0,25 from 0,00025 up to 0,025 from 0,000025 up to 0,0025

Analysis frequency range of the program Narrow-band spectrum for FFT spectrum analyzer А19

Sampling frequency
f, Hz
Range, Hz
Frequency resolution, Hz
250 000 0…100 000 0…10 000 0…1 000 0…100 0…10
from 2,5 up to 2500 from 0,25 up to 250 from 0,025 up to 25 from 0,0025 up to 2,5 from 0,00025 up to 0,25
50 000 0…20 000 0…2 000 0…200 0…20 0…2
from 0,5 up to 500 from 0,05 up to 50 from 0,005 up to 5 from 0,0005 up to 0,5 from 0,00005 up to 0,25
25 000 0…10 000 0…1 000 0…100 0…10 0…1
from 0,25 up to 250 from 0,025 up to 25 from 0,0025 up to 2,5 from 0,00025 up to 0,25 from 0,000025 up to 0,025
5 000 0…2 000 0…200 0…20 0…2 0…0,2
from 0,05 up to 50 from 0,005 up to 5 from 0,0005 up to 0,5 from 0,00005 up to 0,05 from 0,000005 up to 0,005
2 500 0…1000 0…100 0…10 0…1 0…0,1
from 0,25 up to 25 from 0,025 up to 2,5 from 0,0025 up to 0,25 from 0,00025 up to 0,025 from 0,000025 up to 0,0025
500 0…200 0…20 0…2 0…0,2 0…0,02
from 0,005 up to 5 from 0,0005 up to 0,5 from 0,00005 up to 0,05 from 0,000005 up to 0,005 from 0,0000005 up to 0,0005
250 0…100 0…10 0…1 0…0,1 0…0,01
from 0,0025 up to 2,5 from 0,00025 up to 0,25 from 0,000025 up to 0,025 from 0,0000025 up to 0,0025 from 0,00000025 up to 0,00025

Supported Hardware

Input data for Narrowband spectrum program includes digital data of the ZETLAB server channel.

FFT Analysis is a part of the following software:

Narrowband spectrum analysis is included into the Signal Analysis software group.