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Sr. Member
Posts: 1,916
Reply with quote  #31 
wiki say:
The DFT is obtained by decomposing a sequence of values into components of different frequencies"

It is fine for me

Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.

Sr. Member / Supporter
Posts: 310
Reply with quote  #32 
Originally Posted by electricpete

Hi Ali - I definitely respect your opinion on vibration matters. 

I would add to number 1 - Other examples include periodic non-sinusoidal response to a forcing frequency at 1x. 

I think I have a semantic disagreement with the first sentence of 2.   If you have a non-sinusoidal signal periodic at 1x, there are harmonics present, and I would call them "real", even if they are difficult or impossible for us to visually pick out in the time waveform (we can demonstrate the equivalence by adding the sinusoids together with appropriate magnitudes and phases to recreate the original waveform).   I would agree the 2nd sentence in #2 - the FFT tells us what set of sinusoids is necessary to reproduce a periodic signal.  Some people say the FFT "creates" the harmonics, I would prefer to say that it "reveals" the harmonics that are present in the signal.

In the end again it may be semantics.

Hey Pete!

I also appreciate your knowledge and experience. I learned from you a lot.

It seems that my comment (which stimulated OLi to reply) hijacked the original post. Sorry about that.

Please give me a chance to review my thoughts (especially after your opinion explained [smile]). Maybe I'll need to post here some waveforms and discuss them in order to agree on the conventions and terms. However, I wouldn't be surprised if the reason for the disagreement on this concept is a language barrier or simply my wrong understanding.
Regards- Ali M. Al-Shurafa

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