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Convert white noise to brown

B

Bill Shilelds

Is there a standard for "brown" noise as a test signal?

I have a good white noise generator, giving 4Vpp from 12VDC supply.

What RC network would I fit to the output to limit it to brown?

A starting point for component values would be much appreciated.

Bill Shields
 
P

Phil Allison

"Bill Shilelds"
Is there a standard for "brown" noise as a test signal?


** Brown noise is the same as Red noise.

It is produced from white noise by a - 6dB per octave filter.

I have a good white noise generator, giving 4Vpp from 12VDC supply.

What RC network would I fit to the output to limit it to brown?


** Usually, one uses an op-amp integrator.

A starting point for component values would be much appreciated.

** Depends on the low frequency limit you are after.



...... Phil
 
T

Tim Williams

David Eather said:
That's not right. Pink noise is produced from white noise with
a -3db/octave filter... so you have a bit of a problem... if brown noise
is -6db an octave from pink noise brown noise is -9db an octave from white
noise - but you also claim that brown noise is -12db an octave from white
noise. Both your claims cannot be simultaneously correct.

Wait, which dB are we talking here? If it's dB power, -3dB is half, in
which case white noise is integrated as usual. If it's dBV, it should
be -6dB, in which case I am correct. If it's -3dBV, then such a filter
"doesn't" exist, because you need a transfer function of s^-1/2 to make it.
Thing is, dBs are dBs, so half power is sqrt(2)-th voltage, period. So
where the hell does pink noise actually come from?
Don't call anyone a "fucking retard" it might just bite you in the ass.

I didn't "call" Phalluson anything: it was a statement of fact, not an
opinion. ;-)

Tim
 
B

BillyGates

David said:
I made no differentiation between "statements of fact" or "statements
of an opinion". Regardless of how you want to cut it you were calling
someone a "fucking retard" while you were in fact wrong.

In this case we have to make an exception because, after all, we are talking
about phil.
 
B

Bill Shilelds

An integrator (resistor, op amp, capacitor in negative feedback) is
a near-ideal -6.0206 dB per octave filter (it's not really '6' dB
per octave, that's just the casual approximation).

I would like to see how close I can come using passives.

Can anyone provide the configuration and component values (starting
point) for a suitable RC network?

Bill Shields
 
T

Tim Williams

Bill Shilelds said:
I would like to see how close I can come using passives.

Can anyone provide the configuration and component values (starting
point) for a suitable RC network?

What bandwidth, gain?

Tim
 
P

Phil Allison

"Tim Williams"
"Phil Allison"

Fucking retard! Brown noise is produced from PINK NOISE with
a -6dB/octave filter. From white noise it's -12dB!


** Utterly and completely WRONG !!!


** All 3 Wikis back me up completely

From the one on Brown noise:

" Since white noise is the derivative of Brownian motion (more accurately,
Brownian motion is the integral of white noise, "

Apologise anytime.



...... Phil
 
P

Phil Allison

"whit3rd"
"Phil Allison"
** Brown noise is the same as Red noise.

It is produced from white noise by a - 6dB per octave filter.

Phil is correct; ignore the other comments.


** Thanks.

I built an audio band pink noise generator about 25 years ago and can well
remember the hassle of getting the -3 dB octave slope from 10Hz to 50 kHz
accurate.

The white noise source used was a 8 pin DIL pseudo-random number IC made by
National Semi for the purpose - long obsolete now. It tended to make a
weird steam train like noise rather than pure white.

For accurate white and pink noise, I have relied on a test CD since 1984.

Denon Audio Technical CD: 38C39 -7147

http://www.amazon.com/Denon-Audio-Technical-Various-Artists/dp/B0000034ME


White noise is equal-energy-per-octave, and never
spans all frequencies; if you add an upper frequency limit,
that 'white' noise becomes 'pink'.

** Nonsense.

To convert white noise to pink requires that the whole range be filtered so
there is equal energy per octave.


An integrator (resistor, op amp, capacitor in negative feedback) is
a near-ideal -6.0206 dB per octave filter (it's not really '6' dB
per octave, that's just the casual approximation).


** Such a filter is IDEAL for the job in question as the slope is
exactly -20dB / decade.



...... Phil
 
P

Phil Allison

"Bill Shilelds"
whit3rd
I would like to see how close I can come using passives.

Can anyone provide the configuration and component values (starting
point) for a suitable RC network?


** Try 10k and 1uF ( film) - but you must buffer the output with say a
TL071 wired as a voltage follower.



...... Phil
 
B

Bill Shilelds

** Try 10k and 1uF ( film) - but you must buffer the output with say a
TL071 wired as a voltage follower.

That gives a corner frequency of 15.9Hz with low source impedance,
being sub-audio.

Is that correct??

Bill Shields
 
P

Phil Allison

"Bill Shilelds"
"Phil Allison"
That gives a corner frequency of 15.9Hz with low source impedance,
being sub-audio.

Is that correct??


** Yep.

The buffer gives you a low source impedance.

If you use a TL071, then add a 220 ohm resistor at the output to prevent
instability with capacitive loads.

The noise will be close to Brown down to about 30 Hz.


..... Phil
 
D

Don Klipstein

Why not?
Digitally you can multiply with any thing over a fixed interval.

I would like it noted that a -3dB/octave filter converts white
noise to pink noise, not to brown noise. To convert white noise to
brown/Brownian/red noise, what is needed is -6dB/octave. That is
easier, only requiring an integrator, or a approximation of one
using an RC lowpass filter (already mentioned in this thread).

Meanwhile, there are white noise to pink noise filters achieving
-3dB/octave to something like +/- 1/2 or 1/4 dB from 20 to 20,000 Hz
or so, easy to find by web searching.

- Don Klipstein ([email protected])
 
D

Don Klipstein

No, integration (-6 dB/octave) of white noise is brown/Brownian/red
noise. Pink noise is -3dB/octave from white noise.

This is correct.
Both are incorrect. Brown/Brownian/red is -3 dB/octave from pink,
and pink is -3dB/octave from white. Brown/Brownian/red noise is
-6dB/octave from white noise, as in integrated / antidifferentiated
white noise.

-3 dB is half power, and -6 dB is half voltage. dB and dBV are the
same changes if impedance is constant or considered irrelevant.
If it's -3dBV, then such a

That is a white-to-pink filter, which does not exist exactly. However,
there are useful approximations, especially for the audio frequency range.

True, at least both largely and generally.

Pink noise is only approximated by feeding white noise into a filter
approximating having a -3dB/octave slope. There are circuits easy to
find by web searching that achieve such useful approximations for the
20-20,000 Hz range or so, to +/- 1/2 or 1/4 dB or something like that.

The Wikipedia article on "colors of noise" is correct, except for two
minor issues, and then it's minor:

1. Analogy of white noise to white light: Light with a spectral power
distribution of "pink noise" is very slightly more purplish than blackbody
having color temperature of 7000 K.
Light with a spectral power distribution of "white noise" is very
slightly more purplish than blackbody having color temperature of 9000 K.

+6 dB/octave from white noise is the characteristic of blackbody
radiation having infinite color temperature. Such color temperature
has color being close to that of a deep side of sky blue, very slightly
more purplish and less greenish, and not "infinitely deep blue" or violet.

(However, ideal isotropic radio antennas have a -6 dB/octave
characteristic, due to capture area being a constant times square of
wavelength - their output from reception of infinite temperature thermal
radiation is white noise.)

Light having spectral power distribution of brown/Brownian/red noise
is "equal energy per unit wavelength" "white light", very slightly more
purplish than blackbody having color temp. of 5400 K.

2. That article's plots of spectral power distribution:

That has "flat" being equal energy/power per unit frequency bandwidth,
which makes white noise "flat". However, pink noise has equal power
per unit log of frequency, as in equal power per octave. That makes
pink noise "flat" for most audio considerations. And for visible light,
brown/Brownian/red noise (equal energy / power per unit inverse frequency
bandwidth, which is equal power / energy per unitwavelength bandwidth)
is considered "flat" due to being generally not yellowish / orangish
since it has color close to that of light radiated by a 5400 K blackbody.

<SNIP stuff on name-calling and on someone who is quick to do such>

- Don Klipstein ([email protected])
 
G

Grant

Still, not quite ideal; there's no DC negative feedback in the filter
as described... and there's some terms, like crossover
distortion, that might be an issue at higher frequencies.
So, it'll drift near the power rail and teach someone why
the LM324 is not recommended for audio...

LM324 crossover distortion can be tamed with an output resistor to
ground (or -ve on split rails) to convert the output to Class A.

But I did that for LVDT signal conditioner, not audio for listening.

Grant.
 
P

Phil Allison

"whitless"
"Phil Allison"
An integrator (resistor, op amp, capacitor in negative feedback) is
a near-ideal -6.0206 dB per octave filter (it's not really '6' dB
per octave, that's just the casual approximation).

** Such a filter is IDEAL for the job in question as the slope is
exactly -20dB / decade.

Still, not quite ideal;


** Try learning to read.

Such a filter = one with a nominal -6dB / oct slope IS ideal in terms of
its slope.




...... Phil
 
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