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 Forum index » Instruments and Equipment » Modular Synthesis
The color of noise
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chninkel



Joined: Mar 22, 2006
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PostPosted: Wed Mar 22, 2006 1:38 pm    Post subject: The color of noise Reply with quote  Mark this post and the followings unread

Hello I'm a new member in this great forum. Perhaps a newbie's question for you but :

what are the differences between yellow, blue, red... noises ?
I know white is a full spectral noise, brown is a 6dB low pass filtered white noise and pink is a 3dB ( please correct me if it's wrong ). But what about the others and how can I build them ?
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mosc
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PostPosted: Wed Mar 22, 2006 2:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

welcome

These terms are attempts to associate colors with sound. White Noise is supposed to be flat across the entire audio spectrum. The analogy with light is pretty good.

The other colors are more subjective. AFIK, there are no engineering standards to define these terms. Since red is on the low frequency of the light spectrum, and blue is in the high frequency end, you can guess at what blue noise and the rest would be. Pink noise is found on a lot of different synths. It's usually created by filtering a white noise source with a low pass filter.

So with low pass, high pass, and a few band pass filters, you can make your own noise. How about turquoise noise? Rolling Eyes

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DrJustice



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PostPosted: Wed Mar 22, 2006 3:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi chninkel!

While not engineering standards as such, white, pink and blue noise have commonly accepted definitions. For what it's worth, here is one place where they (and others) can be found.

DJ
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chninkel



Joined: Mar 22, 2006
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PostPosted: Thu Mar 23, 2006 1:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Whaou !!!!

what a noisy rainbow !!! Thank you...

If I understand :
white is full spectrum
pink is white filtered by a 3dB LPF
brown is white filterde by a 6dB LPF
blue is white filtered by a 3 dB HPF (or white - pink)

green , purple ( yes Mosc... purple), orange...

Now I just have to paint my music.

I knew it was a great forum
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Uncle Krunkus
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PostPosted: Fri Mar 24, 2006 3:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Remember though that it is an arbitrary definition to say that pink is white with a 3db LP because you've defined an infinite variety of pink noises! (ie what is the cutoff frequency of your filter?)
According to acoustics standards pink noise is noise which has an equal amount of power per octave. Therefore for most cases white through a LP filter will result in a "type" of pink noise, but it won't be "the" pink noise used by acoustics technicians.
Pedantic little fart aren't I? Wink

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seraph
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PostPosted: Fri Mar 24, 2006 4:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:

Pedantic little fart aren't I? Wink

no, you are spot on Very Happy

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DrJustice



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PostPosted: Fri Mar 24, 2006 6:21 am    Post subject: Reply with quote  Mark this post and the followings unread

It is indeed correct that noise spectra are defined by their power density over the whole spectrum (within a limited frequency range). The power density being 1/f for pink noise. However, for all practical intents and purposes, pink noise is derived by low pass filtering white noise. In fact, this is how the pink noise used by acoustic technicians and everybody else is made. It is plenty good to use a 3dB/oct filter at a very low fc, say 20Hz or below, for audio applications.

It's worth noting that producing ideal pink noise spectra isn't really possible since the power density approaches infinity towards DC.

For an in depth look at pink noise in the digital domain, here is the best reference I know about. There are also many references for pink noise filter RC networks on the net, but I don't know which are the better ones.

DJ
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Rob



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PostPosted: Fri Mar 31, 2006 3:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

DrJustice wrote:
It's worth noting that producing ideal pink noise spectra isn't really possible since the power density approaches infinity towards DC.
DJ
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If I remember correctly the wavelength of the lowest frequency in noise cannot be longer as the distance our planet travelled from the origins of the bing bang since the big bang. But as we were not around at the time of the big bang why should be care?

Btw, pink noise for measurements cannot be made with a single simple lowpass filter, but for the audio range it can be quite effectively made with ten parallel lowpass filters all incrementally tuned an octave higher and mixed with 3 dB decrements higher up (which sort of makes a -3dB/octave shelving filter).

One of the disadvantages of using digital noise is that digital noise actually contains an enormous amount of aliasing. This might not be heard as such, but when used for measurements it can distort the picture quite a lot. Creating pure noise by digital means is not at all straight forward. Real good noise generators for reference purposes in measurements are very, very expensive pieces of gear.

Have fun,
/Rob
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blue hell
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PostPosted: Fri Mar 31, 2006 5:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Rob wrote:

If I remember correctly the wavelength of the lowest frequency in noise cannot be longer as the distance our planet travelled from the origins of the bing bang since the big bang.

Maybe the frequency can't be lower than 1 divided by the time elapsed since the big bang. All DC is an illusion in that light I guess ...

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Uncle Krunkus
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PostPosted: Fri Mar 31, 2006 5:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Which "light" would that be?
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