2 Removing escaped $signs edited Nov 18 '13 at 17:56 Peter K.♦ 17.8k88 gold badges3232 silver badges6565 bronze badges The second trace is probably the phase. You can express the spectral density either as a sine term and a cosine term (in phase and out of phase terms) or as a magnitude and phase angle. In your first example, for your plot you have converted the sin/cos terms into a magnitude, and discarded the phase information. Yes, log power differs from log voltage by a factor of two. \$ 2 \log{(V)} = \log{(V^2)} \$$$2 \log{(V)} = \log{(V^2)}$$. But different ways of calculating FT and inverse FT, or PSD and inverse PSD, put a constant value of \$ \pi \$$$\pi$$ in different places: If you use different methods of calculation, you sometimes find that you have choosen to normalize the FT differently. The second trace is probably the phase. You can express the spectral density either as a sine term and a cosine term (in phase and out of phase terms) or as a magnitude and phase angle. In your first example, for your plot you have converted the sin/cos terms into a magnitude, and discarded the phase information. Yes, log power differs from log voltage by a factor of two. \$ 2 \log{(V)} = \log{(V^2)} \$. But different ways of calculating FT and inverse FT, or PSD and inverse PSD, put a constant value of \$ \pi \$in different places: If you use different methods of calculation, you sometimes find that you have choosen to normalize the FT differently. The second trace is probably the phase. You can express the spectral density either as a sine term and a cosine term (in phase and out of phase terms) or as a magnitude and phase angle. In your first example, for your plot you have converted the sin/cos terms into a magnitude, and discarded the phase information. Yes, log power differs from log voltage by a factor of two. $$2 \log{(V)} = \log{(V^2)}$$. But different ways of calculating FT and inverse FT, or PSD and inverse PSD, put a constant value of $$\pi$$ in different places: If you use different methods of calculation, you sometimes find that you have choosen to normalize the FT differently. Post Migrated Here from electronics.stackexchange.com occurred Sep 19 '13 at 13:38 1 answered Aug 20 '13 at 2:17 david 11111 bronze badge The second trace is probably the phase. You can express the spectral density either as a sine term and a cosine term (in phase and out of phase terms) or as a magnitude and phase angle. In your first example, for your plot you have converted the sin/cos terms into a magnitude, and discarded the phase information. Yes, log power differs from log voltage by a factor of two. \$ 2 \log{(V)} = \log{(V^2)} \$. But different ways of calculating FT and inverse FT, or PSD and inverse PSD, put a constant value of \$ \pi \\$ in different places: If you use different methods of calculation, you sometimes find that you have choosen to normalize the FT differently.