Anyone know anything about signal processing?

[cchen]

I just started my internship and I have a question. I was comparing two simple sinusoids for test signals and my mentor asked me a question which I am thinking about. What happens when the frequency of the sinusoid goes above 1000?

 

[Pastore]

wtf is a sinusoid? sounds like its gonna eat me

 

[satori]

Unless I've forgotten all my DSP stuff, I don't think we can give you an answer w/o knowing more information. Maybe it's being put through a high-pass filter, so going above 1k will filter the output.

 

[crypticlogin]

What exactly were you testing for? And yeah, we need more info if you want to know more.

 

[DAM]

cchen: yeah i was thinking that there had to be more info, but since i just got into this stuff i feared that i would be totally wrong. so what kind of test are you doing on these two signals?



dam()

 

[cchen]

well basically my mentor was making me make up these test signals just to play around with them in matlab
i.e.:
n=(0:999)/1000;
A=10;
f=50;
xi=A*sin(2*pi*f*n);

then i changed around the frequency.... what happens when the frequency is greater than 1000? the only conclusions that i can make is that there are more cycles per second, the phase is changing by a greater number, and that the signal is moving much faster.

 

[StormRider]

Here's a hint ---> Nyquist.

 

[cchen]

I have heard and read about that term but I am unfamiliar with it(I am just beginning to learn about dsp)

Please help!

 

[Linflas]

Take a look here.
More in depth here.

 

[Demon-Xanth]

Nothing special happens unless he's referring to the frequency/sample rate. If you drop below 10 samples per cycle you end up with aliasing.

 

[cchen]

I think I figured it out... when you get to a certain frequency, the signal begins to break down because there are less data points, so the signal doesn't even look like a sine wave anymore.

 

[StormRider]

Yes, that's basically what is happening. There's something confusing with my wording (below) of what is happening but here goes:

According to Nyquist, you need to sample at twice the frequency rate of the signal to avoid aliasing.

So, basically you are sampling at 1000 cycles per second (by plotting 1000 points per cycle of the sinosoid)

But if you increase the sinosoid's frequency to 1000 Hz, you need to need to increase the sampling rate (by increasing the number of data points)

 

[cchen]

thanks so much for the clarification!

 

[Helpless]

"We get signal."