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 Forum index » DIY Hardware and Software » Thomas Henry designs
Suggest a Noise Circuit
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DanRilley



Joined: Dec 05, 2009
Posts: 3
Location: Sweden

PostPosted: Thu Jun 03, 2010 9:01 am    Post subject: Suggest a Noise Circuit
Subject description: Looking For a Simple Noise Synth
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Hi, I have a random noise source that generates a random resistance. I want to be able to connect the random resistance to an oscillator to realize the noise in sound waves. Can anyone suggest a circuit that might sound good with this? The resistance fluctuates between 100K and 1M. Currently I am using a simple 555 square wave which works ok but it's a bit boring and hard on the ears.

I suppose it would be a resistance controlled oscillator or noise circuit that I need, but one that sounds nice.

I plan on using the sound generated as a background drone for a concert. Simple and small are nice.

Dan
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Tim Servo



Joined: Jul 16, 2006
Posts: 924
Location: Silicon Valley
Audio files: 11

PostPosted: Thu Jun 03, 2010 5:21 pm    Post subject: Suggest a Noise Circuit Reply with quote  Mark this post and the followings unread

Hey Dan,

I think you would be better off with a VCO (Voltage Controlled Oscillator), and then use a noise source or some other random voltage source as a modulation source to change the frequency of the VCO.

One place I might suggest looking would be a bunch of simple circuits by Nikolas:
http://electro-music.com/forum/topic-34550.html

There are links here to a simple VCO and a simple noise source that should do the trick for you. One note: if you modulate a VCO with noise, you'll get a "grainy" tone that stays at the same pitch. If you're looking for the pitch of the VCO to change over time, then you might want to filter the noise to produce low frequency "red noise." Either that, or use the noise source and a sample/hold module to produce random voltages.

If you really want to stick with the oscillator you already have, then you could use a Vactrol as a resistor. A Vactrol is an LED and photo-resistor in a single package. You drive the LED with the noise source, and the photo-resistor will change resistance depending on how bright the LED shines. Look up other Vactrol circuits, and you'll see how they are normally driven (like any LED, you have to limit the current going through them or else you'll damage the it).

And since I'm here in the Thomas Henry forum, I'll plug the series of Thomas Henry books I publish though Magic Smoke Electronics. This includes "The Noise Generator Cookbook." I'm working on the VCO Chip Cookbook as we speak and hope to have it ready soon. Wink
http://stores.lulu.com/magsmoke


Tim (plugging away) Servo
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DanRilley



Joined: Dec 05, 2009
Posts: 3
Location: Sweden

PostPosted: Thu Jun 03, 2010 6:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Tim, thanks for the response. I will check out these circuits, but the purpose of my project is to visualize (or in this case audioize) the specific noise that I am measuring. I know the grainy sound you are talking about, I think that's what I have now, but it is necessary that the project use this specific resistance. I've used vactrols before so I may try that, but sample and hold could be much more interesting I think, I will look up thanks for the ideas.
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