Frequency Filtering of the vb Instrument's Overall rms Calculation

The information provided is for help with Commtest Instruments products:

• Ascent®/MAS VB, vb instrument

QUESTION

Which low frequencies are filtered out of the instrument's overall rms calculation?

SOLUTION

The only low frequency component that is ignored in the overall rms calculation is the 0 Hz or DC component.

MORE INFORMATION

With Ascent/MAS VB 7.30 sp2 or later, you can specify an Fmin for your measurement to zero-out low frequencies in your measurement. Consult the online help or Instrument Reference Guide under the heading 'Fmin'. In Ascent/MAS VB you can set up a band alarm to monitor the overall rms within a specific band of frequencies. To do this:

• Plot the spectrum that you are interested in.
• Right click with the mouse at the horizontal position where you want the band to start and select Alarm Bands>Add.
• Move the mouse pointer over to the frequency at which you want the band to end (you will see an alarm band 'rubber banding' and following your mouse pointer).
• Click the left button to 'drop' the band.
• Double click on the band and change the Peak/RMS setting to FFT Power RMS.

You will see the current band rms value on the chart now. This will appear on all recordings for that location now.

FAQ ID: 11703 Last Reviewed: 03/01/2001