Differences

Use the Database Tools > Filters > Differences menu option (DIFF GX) to calculate differences between values in a channel.

The option is also available in the Moving Platform Gravity > 1D Filters menu.

Differences dialog options

Channel to difference

Select input channel.

Script Parameter: DIFF.IN

Output difference channel

Select output channel.

Script Parameter: DIFF.OUT

Number of differences (>=1)

Number of differences.

Script Parameter: DIFF.NUMBER

Normalize differences?

Select normalize difference "No", "Yes" (Default No). Output values are divided by 2 raised to the number of differences, e.g. for the 4th difference the values are divided by 16.

Script Parameters: DIFF.NORM

Application Notes

The common fourth difference can be calculated by specifying 4 differences. Fourth differences are useful for identifying noise in the data.

Differences with a dummy, result in a dummy.

Even numbers of differences produce properly located results. Odd numbers of differences will locate the result 1/2 element below the actual location.

The difference filter is calculated by the subtraction of the successive data values of the channel:

D1(V(i)) = V(i+1) - V(i)

Higher differences are formed by successive operations, for example:

D2(V(i)) = V(i+1) - 2V(i) + V(i-1)

D3(V(i)) = V(i+2) - 3V(i+1) + 3V(i) -V(i-1)

D4(V(i)) = V(i+2) - 4V(i+1) + 6V(i) - 4V(i-1) + V(i-2)