# Sign of DC Component obtained from FFT differs with the sign of Mean of the signal, Does the sign really matter?

I've been working on 3-axis accelerometer data to predict the gesture of an user.

Lot of literature pointed me to consider Frequency domain features for my problem and i'm using

1. Mean of the signal on each axis first
2. 'k' coefficients of DFT of the signal.

Since X(0) is essentially the DC component of the signal, i tried checking the DC component with the Mean of the signal and observed they differ in sign because of the sqrt(X(0)*conj(X(0)))/N gives only positive value.

Will it affect my problem in any means?

• Are you confusing the DC component (X(0)) with the magnitude of the DC component (abs(X(0)) ? The DC offset of an accelerometer is the former. Dec 5 '15 at 22:01
• I mean the magnitude of the DC component. I could see since it is the magnitude it cannot be negative. But isn't the Mean of signal represents DC offset? I'm sorry for my ignorance, i'm a computer science guy and not much into signal processing. Dec 5 '15 at 22:18
• See this question: dsp.stackexchange.com/questions/21583/…
– MBaz
Dec 5 '15 at 22:37