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MSD Software Manual PRELIMINARY Release Chapter 10 FFT Spectrum Analyser.

10.2 Relative Offset Display. 

The Display Relative [REL] function works in conjunction with the Set relative

[SET REL] function and the CURSOR Select function. When applying the

display relative function, by pressing the [REL] key, the MSD tries to shift the

whole FFT curve up or down relative to the [SET REL] level until the cursor

level reading is equal to zero dB. The relative level is defined as the measured

level at the cursor location at the exact time when pressing the [SET REL]

Key. Use the [] / [] keys to move the cursor to a specific bar of the FFT.

The numeric frequency of the selected bar and the actual measured level is

displayed in the bottom right corner of the FFT display.

The [SET REL] key will only manipulate the on-screen data and should

generally not be used to raise a weak signal, since accuracy will be lost.

The resolution of the spectrum analyser is far higher than that of the screen

resolution. Consequently, not all analysis results are displayed directly on

screen. However, the frequency cursor can be used to obtain this 'hidden' data

since it will display the exact frequency resolution in the numeric field display.

Note that the numeric readout corresponds to the selected function. The

numeric values always follow the actual data on the screen, i.e. if any of the

functions REL and REF have been selected the numeric readout will reflect

this.

10.3 Hold Maximum Level. 

The FFT HOLD function will disable the curve fall-back function, and thus show

the maximum value of the level within each frequency band since the [HOLD]

key was activated.

10.4 FFT Zoom Function. 

The full frequency range of the spectrum analyser can be changed by a factor

of ten. This means that the display will alter from showing a range of 46Hz to

23.531kHz, to showing only the lower frequency range of 4Hz to 2.353kHz.

When activating this function by pressing the [ZOOM] key, a much more

detailed look at the important low frequency signals is obtained.

10.5 Relative Memory FFT Measurements.

 

The ‘OP-Mode’ menu is used to display the spectrum analysis relative to a

temporary or predefined reference curve. The relative display functions can all

be active at the same time. To access the ‘OP-Mode’ menu from the ‘FFT-Main

Menu’ press [More…] and then [OP-MODE].

When measuring against any of the two reference curves the FFT result is

displayed relative to this curve, frequency bar by frequency bar. In that way if

measuring an Input signal relative to itself it will result in a flat response around

0 dB. (this is simply done by first pressing the [SETMEM] key follow by the

[I+MEM] key.

The memory function is sensitive to the Write-Protection setting. If Write-

Protection is on the [SET MEM] can only be used for temporary storage. The

Analyser will loose the stored data each time the function is exited. This is very

useful when making repeat measurements like the testing of room acoustics,

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DK Digital CDB-600 Spécifications Page 43

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