Anybody know how to input a 20db/octave slope in matlab?

[FusionITR]

I'm new to using matlab and I was wondering how do make a graph with a -20db/octave slope for modeling filters?

For example, say I want to make a graph where y = 0 until 1000, then i want the graph to have a -20db/octave slope until 100,000.

Anybody know how ot put a function like that into matlab?

 

[FusionITR]

Anybody? Could use some help....

 

[Russlk]

Did you mean 20 dB per decade? One R-C filter rolls off at 20 dB per decade or 6 dB per octave. I am not familiar with Matlab, but it should automaticly display in semi-log form.

 

[FusionITR]

Ugh yes I meant decade, not octave sorry.

Yeah, I meant that I wanted to know how to make a slope of 20db/decade without putting in a actual transfer function.

 

[audioguru]

A simple filter with a series resistor then a capacitor to ground makes a 20dB/decade lowpass filter.
Why sim such a simple filter. You should see its gradual rolloff with your eyes closed.

 

[Russlk]

"Yeah, I meant that I wanted to know how to make a slope of 20db/decade without putting in a actual transfer function."

Sorry, that does not make sense.

 

[FusionITR]

"Yeah, I meant that I wanted to know how to make a slope of 20db/decade without putting in a actual transfer function."

Sorry, that does not make sense.

This is want I want to do.

Make a semilog plot from 1 to 1MHz. Take a abitary point (say f = 1kHz) and make a slope of -20db/decade unti say f=100kHz then go flat again.

Something like this:

**broken link removed**

This is in no way a strange question to ask, as there are already matlab gui's that do this such as https://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=2664&objectType=file

I just wanted to know if anybody here knew how to put this into matlab. I am very new to matlab (just got it last week) and have no idea how to do this.