question about modualted Gaussian pulse in CST

In CST, once I input some values in frequency setting dialog, a default modulated Gaussian will be given by CST automatically.
so what is the objective in the determination of this modulated Gaussian pulse, shortest simulation time or best simulation results? how can I know the pulse parameters, i.e. T, t0, ws, are optimal values? actually i tried several modulated Gaussian pulse with different pulse paramters, really cannot tell which one is the best.
would anybody offer me some inspirations? thanks a lot in advance.
regards,
tenderne

pls~~~~ anybody, any idea or suggestions~~~~

CST is time domain EM simulator, frequency domain response is extracted by using FFT after time domain results are got. Based on the frequency range you want to simulate, the CST will help you to shape the modulated Gaussian pulse to cover the frequency range. For general usage, I have not encounted the situation where the pulse shape has the effect on frequency domain simulation results.
Regards,

hi, asdfaaa
thank you very much for your reply.
'Based on the frequency range you want to simulate, the CST will help you to shape the modulated Gaussian pulse to cover the frequency range.'
I understand CST automatically generate an 'optimal' modulated Gaussian pulse to cover the interested frequency range. However, I want to know how cst choose this kind of 'optimal' pulse. To make it more clearly, I want to know how cst determine the modulated gaussian parameters, i.e, ws, T, t0. so would you please give me some hints? thanks.
regards,
tenderne

ermm.... maybe you can try do FFT to evaluate the relationship between modulated gaussian pulse parameters (ws, T, t0) and their corresponding spectrum.
Regards