Noise Results from Transient Noise Simulation and Noise Simulation

Dear all,

     I am analyzing the noise performance of a simple RC circuit in the 20-20kHz band.

     I have used two different methods in order to compare the differences.

     Method 1 (With .noise simulation):

     Integrated noise power at Vo (20-20kHz) = 331.2 fV^2. 

     Expression used: integ((getData("out" ?result "noise")**2) 20 20000 " ")

    Method 2 (With Transient Noise Simulation + FFT):

    SNR (20-20kHz) = -6.371 dB,  Signal Power = 1.179 pV^2,  Integrated noise power at Vo (20-20kHz) = 5.113pV^2

    SNR: spectrumMeasurement(VT("/VO") t 305.17578121E-9 1.00030517578125E-3 32768 20 20000 0 "Rectangular" 0.0 0 1 "snr")

    I see that there is a discrepancy in the integrated noise power between the two methods (highlithed in red).

    I suspect that this is due to the FFT (white noise from fs/2 ~ inf is folded back into 0 ~ fs/2).

   Could you please suggest me a method to align these two results?  Should I add a low-pass filter here?

Thank you very much

Kenny