irmurray wrote:Hi folks,

In the Expression Evaluator, I can create a single-frequency tone using an expression such as:

sin(2*pi*f*t)

The spectrum of this would be a peak at a single frequency (left diagram below).

My question is how to create a signal like that on the

*right *- still a single peak but with a

**spread** of frequency components.

I want to create this peak formulaicly, I don't want to filter it from white noise.

Thanks for any suggestions.

Regards,

Iain.

Code: Select all

`y^cos(2*pi*(f/x)*t)*sin(2*pi*f*t)/y`

f = Frequency (make sure to pay attention to what I said below about x if you want this to be the center frequency.)

y = Amplitude (1 = single frequency tone. numbers above 1 = the higher the number, the louder the spread of frequency components.)

x = Bandwidth (1 = f becomes the fundamental as opposed to the center, and all frequency components are multiples of f. numbers above 1 = the higher the number, the closer the frequency components are together with f. Also the higher y is, the higher x needs to be in order to create symmetry of the frequency components on either side of f. The higher y becomes without raising x, the more lopsided the frequency components will be above f.)

Here are some values to start you out with something, enter the equation I posted above into the Expression Evaluator and enter the variables I'm about to put below. After that check out the Spectrum Visual and see if it looks like what you had in mind (make sure to have the FFT Size high enough to see the peaks good). Here are the variables:

f = 1000

y = 1.5

x = 50

The best way to understand what values are going to do what is to just try different values and observe how it changes the spectrum after each change. I'm no math wiz, I just figured out everything I said above by tinkering around with the variables, so hopefully you'll figure it out as well! Have fun.