Hello ankit,
Thanks for your post! I see you are using the Frequency Response Functions. Is the reason you want to use this function to perform your fractional octave analysis is so that you will still get the magnitude, Phase and Linear Frequency? It sounds like the "SVT Third-octave Analysis.vi" would do what you want to do. This VI will allow you to set the frequency range and the type of averaging it will do. You can find this function by going to Sound and Vibration >> Octave Analysis >> SVT Third-octave Analysis.vi.
Please post back if you have any other questions!
Corby_B
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