I just wanted to express the Normalized part of the magnitude axis label using the Normalized function. True,Normalized will just find a factor that is applied to all numbers, and one just has to pick the right norm. Here is an example of how to scale a list of non-negative random numbers such that the maximum is 1 after normalization:

In[1]:= mag = RandomReal[{0, 100}, {10}];

In[2]:= Max[mag]
Out[2]= 99.6271

In[3]:= magNormalized = Normalize[mag, Norm[#, \[Infinity]] &];

In[4]:= Max[magNormalized]
Out[4]= 1.

The reason for using Normalized is to make the intention clear, but there are also situations where it is convenient to use Normalized since the data (in this case mag) does not have to be repeated. In the end, the result is the same as:

magNormalized = (1 / Norm[mag, \[Infinity]]) mag;

Thanks, and no need to be sorry. Neither is my idea to argue with you. This is a fruitful discussion which I believe will be of interest to other users as well.

I think that the key here is the word normalized on the magnitude axis. Looking at the plots, it seems like normalized magnitude applies the scaling necessary to make the maximum magnitude 1. With such normalization, dB makes perfect sense! Also, with normalized magnitude in the axis label, the risk of confusion is more or less eliminated.

At the moment, this type of FFT plot cannot be made with SystemModeler, but if you have access to Mathematica, you can always run your simulations with WSMSimulate and then use Fourier, Normalize (with the infinity norm expressed using Norm) and the rich plotting capabilities of Mathematica to obtain a normalized FFT plot.

Thanks again for clarifying your suggestion. Your feedback is valuable.

I'm not very familiar with antennas either, but they appear to me as systems rather than signals. I could understand how you could feed a spectrum analyzer with an input/output pair to estimate damping and phase shift as a function of frequency, and then plotting in dB makes sense to me. What I still don't see is how dB makes sense when applied to one signal at a time, as in the SystemModeler FFT analysis.

It would be very useful to us to see examples where dB is used on the FFT magnitude of a single signal. Do you have any references where such use is explained?

Thanks in advance.

I can't really answer about quantizers, as that is not my field of expertise, but thanks for suggesting dB magnitudes in the FFT analysis!

Note, however, that the FFT analysis applies to a signal and not to a transfer function (system). As far as I know, it is not common to use dB magnitudes for signals, so it seems like there would be some risk of confusion if the magnitude axis were measured in dB; someone reading the plot may think that it is an estimate of the Bode plot of a system rather than the FFT of a signal.

Thanks, David. You gave an excellent argument for plotting signals in dB.

Others are still encouraged to chime in!