Bedrock SM30, Руководство по эксплуатации

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38 Bedrock SMxx operating manual © Bedrock Audio BV, 2019
The minimum and maximum frequency that can currently be displayed are indicated at
the top of the screen, as well as the exact frequency at the cursor position and the level at
the cursor position.
The second screen of the FFT module allows you to set an integration time for the FFT
analysis. If the integration time is set to “infinite,” then the instantaneous spectrum is
shown. The graph on the display will show rapid fluctuations. In general, the longer the
integration time that is chosen, the more accurate the spectrum.
The third screen of the FFT module (“settings”) is where the parameters of the FFT algo-
rithm are controlled.
The window size determines the frequency resolution of the FFT analysis. The number
of spectral lines is exactly half the window size. At the maximum window size (32768),
the audible frequency range is analyzed in16384 spectral lines. Shorter windows offer less
detail, but the analysis runs quicker allowing for shorter integration times to arrive at the
same accuracy.
The type of window to be applied can also be set in the graphics screen. Each type of win-
dow (blackman, hamming, rectangular, etc) is associated with a specific set of advantages
and disadvantages relating to the FFT analysis. We recommend studying the literature on
spectral analysis, or one of the many available online resources, to choose the window that
best suits your application.
For most non-critical applications, the settings selected by default (hamming window with
a window size of 8192 samples) are a suitable choice.
Some remarks about the FFT module:
• The elapsed measurement time is shown above the progress bar. If the in-
tegration time is set to “continuous,” the instantaneous spectrum will be
shown.
• The FFT module is recommended whenever a high frequency resolution
is needed. To obtain standardized spectral measurements, where the exact
levels at standardized frequencies are of prime interest, 1/3 or 1/1 octave
band measurements through the RTA module are the best choice.
• Saved data can be retrieved over USB and imported in MS Excel or any
other program capable of dealing with .csv formatted data. This is the same
as all other modules. However, the FFT module is capable of producing
much more data (up to 32768 data points and frequencies for a single meas-
urement). Not all spreadsheet programs may be able to import that many
columns, which is why the data is organized in rows rather than columns.