[sdiy] Various colors of noise.

[Tom Wiltshire]

There's a similar heavily-filtered noise source ("infra-red" noise) in the Polyfusion synth schematics.

One problem with this way of generating this type of wandering modulation voltage is that the voltage level is heavily reduced on average, but adding gain to bring it back up is uncertain since the potential maxmium level isn't really decreased at all. E.g. if you add gain, it'll clip - not often, but probably sooner or later.

I've used cosine interpolation between random points to generate a similar waveform digitally. That avoids this issue, and has the advantage that you get some level of control over how fast the waveform changes too.

Tom

> On 4 Mar 2026, at 04:19, Michael E Caloroso via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> Few people realize that the venerable Minimoog includes red noise.  But it's a modulation source not audio.  The front panel NOISE switch alternates between white and pink noise as an audio source, and also between pink and red noise as a modulation source.  Red noise as a modulation source sounds like smoothed S&H.
> 
> MC
> 
> On Tue, Mar 3, 2026 at 6:14 PM Thomas Hudson via Synth-diy <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
> BTW, while researching creating green noise I came across a website for a Mac and iOS app:
> 
> The original free color noise generator on the Internet. Hear what your mind has been missing…
> simplynoise.com
> <cropped-web_sn_appicon_512-1-180x180.png>
>  <https://simplynoise.com/>The original free color noise generator on the Internet. Hear what your mind has been missing… <https://simplynoise.com/>
> simplynoise.com <https://simplynoise.com/>	<cropped-web_sn_appicon_512-1-180x180.png> <https://simplynoise.com/>
> 
> In addition to noise colors, t also has beach sounds, fireplaces, babbling brooks, etc.
> 
> Fun little app.
> 
> 
>> On Mar 3, 2026, at 5:56 PM, Thomas Hudson via Synth-diy <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
>> 
>> Interesting idea and article. 
>> 
>>> On Mar 3, 2026, at 4:58 PM, Mike Beauchamp <list at mikebeauchamp.com <mailto:list at mikebeauchamp.com>> wrote:
>>> 
>>> Hi Thomas,
>>> Maybe take all of the different noises, and feed them into an interpolating scanner circuit (like this one: https://till.com/articles/scanner/ <https://till.com/articles/scanner/> ) and from there you could control the output noise colour (and anything inbetween) with the wandering CV.
>>> 
>>> I wonder if the different noise colours all need to be derived from a single source for the crossfading to work.
>>> 
>>> Mike
>>> 
>>> 
>>> On 2026-03-02 18:20, Thomas Hudson via Synth-diy wrote:
>>>> I have an analog module that can generate blue, white, pink, and red (brownian) noise. I’m interested in how I might create a random walk using perhaps a sample/hold and smoothing function to produce a sort of wandering control voltage from each of these noise sources.
>>>> I also was recently introduced to green noise. From Wikipedia:
>>>> * The mid-frequency component of white noise, used in halftone
>>>>   <https://en.wikipedia.org/wiki/Halftone <https://en.wikipedia.org/wiki/Halftone>>dithering
>>>>   <https://en.wikipedia.org/wiki/Dithering <https://en.wikipedia.org/wiki/Dithering>>^[19]
>>>>   <https://en.wikipedia.org/wiki/Blue_noise#cite_note-19 <https://en.wikipedia.org/wiki/Blue_noise#cite_note-19>>
>>>> * Bounded Brownian noise
>>>> * Vocal spectrum noise used for testing audio circuits^[20]
>>>>   <https://en.wikipedia.org/wiki/Blue_noise#cite_note-comp.dsp_FAQ-20 <https://en.wikipedia.org/wiki/Blue_noise#cite_note-comp.dsp_FAQ-20>>
>>>> * Joseph S. Wisniewski writes that "green noise" is marketed by
>>>>   producers of ambient sound effects recordings as "the background
>>>>   noise of the world". It simulates the spectra of natural settings,
>>>>   without human-made noise. It is similar to pink noise, but has more
>>>>   energy in the area of 500 Hz.
>>>> Wondering how I might generate this other than using something like a bandpass filter tuned to 500 Hz using pink noise. I want to generate it in the analog realm.
>>>> TIA,
>>>> Thomas
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