[sdiy] Popcorn Noise Generator?

[Magnus Danielson]

From: harrybissell <harrybissell at prodigy.net>
Subject: Re: [sdiy] Popcorn Noise Generator?
Date: Fri, 08 Jul 2005 22:50:13 -0400
Message-ID: <42CF3B63.F2E6E0CC at prodigy.net>

> Magnus Danielson wrote:
> 
> > Considering that it has the powerlaw of 1/f², a -6dB curve would do the trick.
> 
> as usual you are about to lose me :^P

Not my intention, trust me!

> I thought the 1/f^2 was more a probability rating. Isn't the spectral
> (harmonic) distribution of a single event different than this. The louder
> pops would be less frequent, smaller ones would be more frequent... but
> harmonically they would still be a 'pop' ???

No, the 1/f² powerlaw is the frequency distribution. It is the powerlaw
knowledge that steeres the filtering of white noise to create various other
noise forms. The -3 dB slope (powerlaw of 1/f) is the expensive ones, the -6 dB
slopes comes from integrations so you can get flat (white), 1/f (-3 dB), 1/f²
(-6 dB), 1/f³ (-3 dB followed by a -6 dB) and 1/f^4 (-6 dB followed by -6dB).

What you describe is the amplitude distribution, and one such distribution is
the Gaussian which have the "the higher amplitude the less frequent" aspect
that you are after. Just to make people more confusing, white noise may have an
Gaussian distribution, but the Gaussian distribution is not guaranteed just
because it is "white noise". If you have a PRBS generating noise, it appears to
be white noise, but the amplitude distribution is not gaussian, rather you have
a +A/2 and -A/2 amplitude peaks being of 1/2 each.

> > Infact, since some pop-corn noise is already in place in the low low bottom,
> > the corner frequency would just be a cross-over between actual and synthesized
> > pop-corn noise. So, use a normal white-noise source and then integrate it.
> > That should do the trick.
> 
> Wouldn't that be quite inaudible ???

You are forgetting that the "pop" you hear is the speakers or headphones
responce to an unlikely DC shift. We *are* talking low-frequency here!

> > > alternately you could get an old Gershon Kingsley record and have some
> > > REAL popcorn noise...
> >
> > Yes, but I was going to propose to apply the right kind of packet to the
> > microwave oven... :P
> 
> Maybe an old CD in the microwave oven ???

I thought they only made a cracle... I am tempted to test...

Cheers,
Magnus