Signal calculator |
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By choosing *System control/Signal calculator* option from the main menu or pressing
toolbar button, you can start one of the most useful tools in *SIGVIEW*, the Signal calculator.

Just as a standard calculator is used for calculating expressions with numbers, *SIGVIEW*’s
calculator can be used to combine signals or instruments in different arithmetic or signal analysis
expressions. You can use it, for example, to add or subtract two signals or spectrums or to
perform different cross-spectrum calculations.

In the upper left box, the names of all existing signal or instrument windows (loaded signals, FFT
results, etc.) in your *SIGVIEW* workspace will be shown. You can choose to display all windows,
only instruments or only signal-like windows (containing sequences of values).

As the alternative to choosing windows in the list, you can also do it graphically:

Below the list, you see a graphical display of your workspace, just as in __Control
Window__. By
simply clicking on an icon, the corresponding window will be added to the expression window on
the right side. If certain window is not suitable to be added to the current position in the
expression, your mouse cursor will change to and you will not be able to add it to the
expression.

The list box on the right side will contain the new expression for the evaluation.

At the bottom of this dialog, various buttons with all available calculator functions are shown. Only
functions which are available in the given context will be enabled. For example, only after you add
a signal window to your expression, a binary function buttons like "+", "-", "/",... will be enabled.

You can move signals from the left to the right box (include them in the expression) by double-clicking their names or selecting them and pressing the ‘>>’ button. For example, to subtract two
signals, simply select the name of the first one, press ‘>>’ button to add it to the expression, then
press ‘-’ button, and finally add the second signal to your expression.

When you create the complete signal expression, click OK to create the result signal. It will be __linked__ to all windows included in the expression
and will recalculate and redraw each time they
change. In case that one of expression windows is deleted, the calculator window will be frozen
and will keep its last values.

· **sqrt **(square root)

· **log **(log_{10})

· **x^2 **(squared)

· **abs **(absolute value)

· **2*** (multiply with 2)

· **10*** (multiply with 10)

· **(1/2)*** (multiply with 1/2 i.e. divide with 2)

· **(1/10)*** (multiply with 1/10 i.e. divide with 10)

· **sin, cos, tan, atan: **trigonometric functions

· ***** (multiply)

· **/** (divide)

· **+** (plus)

· **-** (minus)

· **Convolution **(convolutes first signal with the second one)

· **Smooth with** (smooth first signal by using the second one as a weighting
function)

For further information about Order Analysis functions, __see Order Analysis chapter__

If only simple arithmetic binary functions (*, /, +, -) are used, you can freely mix instrument and
signal windows in the expression.

If you include two signals of different lengths in a binary operation (for example you subtract one
signal from another one), *SIGVIEW* will use only a part of the longer signal (starting from its first
sample) which has the length of the shorter signal.

Here are some examples of calculator expressions.

You have loaded two signals, calculated their spectrums and you have the following workspace:

Now, you would like to subtract two calculated spectrums to get some information about their
differences. To do it, create the following expression in the Signal calculator:

The resulting window will contain th requested difference between spectrums.

You would like to subtract mean value of a signal from all signal values (normalization). First, you
would calculate signal mean by using the appropriate instrument:

Then, you would create the following expression in the Signal calculator:

The result will be a new signal calculated as requested:

You can also have expressions containing only instrument windows. The result of such
expressions will also be a new instrument window.

In this example, we calculate RMS of two signals and then create a new instrument containing
their difference:

There a practically no limitations for creating calculator expressions. Here are some examples: