Why the Labview Function Multitone Generator.vi does not work properly 2?

[Acoustics]

"I use Labview 6.1 and need to get the time domain representation of a signal from the outputs of the Amplitude and Phase Spectrum.vi which are: Ampl Spectrum Magn (Vrms), Ampl Spectrum Phase (radians) and df (Hertz). So, I did the following test. I generated a signal (swept-sine) then I got its frequency representation from the Amplitude and Phase Spectrum.vi. I tried to recover the waveform by the correct conversions of Vrms, radians to the input units of the Multitone Generetor.vi (V, degree, frequency array, # of samples and sample frequency), but I was unsuccessful. The wavefoms were slightly different and I don't understand why. Could you enlighten me?"

[DSPGuy]

FFT magnitude and phase are defined in terms of cosine(cos(theta)+i*sine(theta)), while multitone generation is defined in terms of sine. Try adding 90 degrees to your phase before passing it to the multitone generator. Also, the multitone generator will not reproduce the Nyquist term, so if you have significant energy at Nyquist your results may differ.