USB 6009 Analog In raw data format

[Dennis_Knutson]

You've never really explained why you don't use the F64 data. This is probably what Signal Express is using and you've already said the signal looks fine. As has been already mentioned, the F64 is scaled and calibrated and the other modes are not.

[Audioguy]

I have some existing FFT algorithms that are used when we capture audio, in this case, sine waves. They accept 16 bit integer data, find the fundamental frequency and calculate Total harmonic distortion plus noise. My goal is to capture the audio with the USB DAQ and perform the same measurements. I didn't find any analysis API's that came with the software packaged with the USB 6009 DAQ so I was hoping to use my existing code.

Signal Express does have a distortion module that makes those measurements, but I need to do it programmatically for an automation project and all the existing code is written in C/C++.

[Dennis_Knutson]

I'm sure there exist some FFT routines that use floating point numbers but if you want to use what you have, you would get accurate results if you took the scaled/calibrated F64 values and then converted those to integers.