Kelvin,
The DAQmx driver will give you the tools needed to import a digitized
signal into VB, but once the data is in VB you will need to do analysis
on the imported data (the imported data is a digital representation of
the time domain of your audio signal). LabVIEW and CVI come
with the tools needed to extract the RMS, Frequency, and THD from the
time domain information, this is not the case with VB, C++, etc.
You have two options, one is to purchase Measurement Studio or to write
your own analysis functions in VB. Information about the
measurement studio solution can be found in the message thread below.
http://forums.ni.com/ni/board/message?board.id=232&message.id=1889
Writting your own analysis functions in VB would not be too hard when
determining the RMS, but frequency and THD might prove to be a
difficult task (especially THD).
Like I said above, first you need to digitize your signal using the DAQmx driver and then you need to analyse it.
Hopefully this helps a little bit,
Lorne Hengst
Application Engineer
National Instruments
