[sdiy] Handy DIY tip #213/noise color

[patchell]

    You would have to use a wave analyzer.  You would set the bandwidith
to something like say 10Hz and measure the RMS value of "signal".  If
you have white noise, no matter what frequency you set the wave analyzer
at, you will get the same value.  You can also use an FFT.  Again, you
should see a flat response.  FFT's are kind of neat to do this with,
because you can easily see the 1/f corner, and all that, plus, if there
is anything that is coherent, it really pops right out of the noise.
But if you have two white noise signals that are added together, you
will have a tough time determining how much is from each source unless
you know the value of one of them (remember, in I explained before I
used a 10 ohm resistor as a callibrated noise source)...

Tim Ressel wrote:

> Yo,
>
> Okay, since this got all serious (tsk tsk), I have a
> serious question: Just how do you test the Noise to
> Noise ratio? Or to put it a better way, how does one
> gauge the quality of noise? What is the standard?
>
> --tr
>
> --- Ian Fritz <ijfritz at earthlink.net> wrote:
> > Another example: Suppose you are trying to make a
> > pure white noise source.
> > If the junction you are using is not ideal, you also
> > get some undesirable
> > 1/f or popcorn noise at low frequency.  So that
> > "bad" noise would be the
> > "noise" and the "good" (white) noise would be the
> > "signal".
> >
> >    Ian
> >
> >
> > >In the case of a noise generator, the noise IS the
> > signal, so any signal
> > >contained in the noise, would be considered
> > "noise". A reversal of roles.
> > >
> > >For example, if you fail to bypass the supply to a
> > reversed biased emitter
> > >noise generator, you can get other periodic signals
> > from the power supply
> > >lines. These periodic signals are "noise" since
> > they disturb the gaussian
> > >distribution of the noise (which is the signal of
> > interest).
> >
>
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--
 -Jim
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