FFT
[FFT]
Configure the FFT.
* If you click the position of a button, a combo box, etc. in the figure below, it jumps to the explanation of that part.
- Data length of FFT. (128 to 131072)
Naturally more frequency resolution will increase but calculation time will take more.
Conversely, if the data length is short, the frequency resolution will be reduced, but you can observe the time change of spectrum such as music finely.
(Originally, in order to obtain correct results, it is necessary that the data does not fluctuate during the data length.) In the case of the ever-changing signal such as music, if the data length is long, we can not see small changes)
*The minimum frequency resolution is the sampling frequency sample data number.
(Example) 44100 samples / sec 4096 points For FFT, 10.77 Hz
This value can be displayed at the same time by displaying Spectrum's comment line.
Settings dialog - Spectrum tab - See Editing for comment lines.
Note:
To raise the resolution, we tend to increase the number of sample data freely, but with caution about this.
For details,
About the number of sample data of FFT of hint collection
Please refer to.
*You can not change the number of sample data while calculating &
It can be changed only while stopped.
- Select the window function for FFT.
The following seven types can be selected.
Hanning
Hamming
Blackman
Blackman-Harris
Blackman-Harris 7 Term
Flat top
None (Rectangle)
*Window function (Window Function)
Originally it is a function to multiply waveform data by FFT which assumes that the signal is periodic and continuous, as preprocessing to reduce errors due to cutting out part.
(Please refer to the related specialty book for details.)
Normally, observation of music waveforms, etc., the balance between the display of close-up spectra and separation characteristics is relatively good Hanning window is good.
In the THD measurement and the like, there is almost no decrease in the peak value You can use the Flat top window.
For details, please see About distortion measurement .
*Window functions can be changed in real time even during calculation & display.
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When closing the setting dialog box, When you press the [Cancel] button and close it, all settings up to that point will return to the state when the dialog box was opened.
Therefore, you can temporarily make another setting.
All the settings of the main window, including the setting in the setting dialog, It is stored inWS.INI(WS - 2. INIforWaveSpectra: 2for the second) and reproduced at the next start It will be.
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