[sdiy] Handy DIY tip #213/noise color

[Tim Parkhurst]

Hi All,

Correct me if I'm wrong (like I have to ask, wink), but I thought I had read
that white noise has equal frequency distribution (all frequencies are
perceived to be the same volume across the range of human hearing) whereas
pink noise has an equal energy distribution (all frequencies have the same
power level which, due to the frequency response of the human ear, makes
pink noise sound "darker"). If I've got this right, then I would guess this
would be at least part of what you would look for in analyzing the "quality"
of a noise source. 

Right? Wrong? Fell asleep during that lesson? Criminally insane?

Tim Servo

***************************************************
> -----Original Message-----
> From: Magnus Danielson [mailto:cfmd at swipnet.se]
> Sent: Wednesday, January 15, 2003 4:12 PM
> To: grichter at asapnet.net
> Cc: patchell at silcom.com; madhun2001 at yahoo.com;
> tparkhurst at siliconbandwidth.com; bahi0387 at terra.com.br; synth-
> diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Handy DIY tip #213/noise color
> 
> From: Grant Richter <grichter at asapnet.net>
> Subject: Re: [sdiy] Handy DIY tip #213/noise color
> Date: Wed, 15 Jan 2003 01:25:01 -0600
> 
> > Signal to noise is kind of a misleading term.
> >
> > 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.
> 
> Exactly!
> 
> > 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).
> 
> Actually, you allways have the overtone spectra from the supply, but the
> real
> question is just how much damping there is.
> 
> A good way to measure the "quality" of noise should really be to measure
> in
> dB the autocorrelation of the noise. Normal noise should not autocorrelate
> with
> itself, but any non-noise signal in there would autocorrelate with itself,
> and
> contribute to the autocorrelation. The lower autocorrelation number, the
> better
> quality the noise have. Beyond a certain level I think you could consider
> it
> for most applications to be _only_ noise.
> 
> However, I know there are issues with certain types of noise and
> statistics, so
> ordinary autocorrelation might not have enought "strength". Noise is a
> mighty
> strange thing you know.
> 
> Cheers,
> Magnus



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