Look at the following palette: Sound & Vibration>>Frequency Analysis>>Spectrum Extended Measurements. The VI is fourth from the left in the top row. You can also do a search for 'integration' using the search feature in the LabVIEW palette. I tend to use the search feature a lot until I am very familiar with a palette.
Doug
Enthusiast for LabVIEW, DAQmx, and Sound and Vibration