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 Forum index » DIY Hardware and Software » Thomas Henry designs
Tunable Noise Source
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Thomas_Henry



Joined: Jul 24, 2009
Posts: 129
Location: N. Mankato, MN

PostPosted: Mon May 21, 2012 7:47 pm    Post subject: Tunable Noise Source
Subject description: Sweep that Noise!
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Hi Gang,

I'm almost on break now (I'll be free after the dentist on Wednesday). It's been a crazy school year, but I did get quite a bit of DIY done anyway. For starters, I finally finished my big microcontroller cookbook---that was three years a-coming. And I've got four new synth modules that my cohort Scott (well-known investor in Wild West World) will be releasing.

In the meanwhile, here's something you might find interesting. It's a tunable noise source built around the SN76477. Recall that you can still get these from BG Micro.

Here's the deal. The SN-Voice has a tunable noise source, too. But this new version greatly reduces the parts count. I don't know why it didn't occur to me sooner, but it is possible to put the internal clock under voltage control, and that's what I've done here. With switch S2 you can make the unit sweep up, down or manually set the center frequency. The sweep sounds like a potent filter, but there's no filter to be seen anywhere. In fact, you'll observe that I've completely ignored the SN noise filter. It simply isn't needed since the noise clock sweep is so much more powerful.

The double diodes might perplex you. That took a lot of work to figure out. The EG of the SN really stinks, I think. In particular, the release seems to be too linear for my liking, cutting off in a fairly unnatural manner. The diodes keep the clock sweep from falling below the EG cutoff. Try the circuit without and you'll see what I mean.

Here's what you can expect. This is a noise source, obviously. In manual mode you can set it for high pitched hiss, like steam escaping, or low pitched gravelly sounds like crushed rock falling from a dump truck. The other two settings of S2 either sweep the center frequency up or down under EG control. Sweeping down is perhaps more natural for doing percussive effects.

This could easily form the heart of a new snare voice. Notice that I haven't even touched the LFO or VCO, so both are still available. Again, the idea here is to make a tunable or sweepable noise source with fewer parts than the SN-Voice. The sound is much the same.

I've shown it with a pushbutton, but obviously you can fire it with a gate signal from a synth. Remember, this is an AR type of unit.

I'm really excited to get the sweepable noise sound with so few parts and wish I had thought of this 35 years ago. Let me know what you think.

Thomas Henry


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inlifeindeath



Joined: Apr 02, 2010
Posts: 315
Location: Albuquerque, NM

PostPosted: Tue May 22, 2012 10:02 am    Post subject: Reply with quote  Mark this post and the followings unread

so awesome and exciting to see a new post from you and learn there are new projects and cookbooks on the way! you rock Thomas and Scott!!!
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jumunius



Joined: Apr 19, 2010
Posts: 346
Location: San Francisco, CA
Audio files: 13

PostPosted: Tue May 22, 2012 11:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Very exciting! I think this forum could use a kick in the pants, and a couple new projects should do the trick.

Seeing as I have stuffed, but not wired, my SN Voice pcb (need a 2nd cabinet first!) I wonder if I should incorporate some of this as mods to my SN Voice. Particularly in terms of the use of noise clock / pin 4 instead of noise filter pin 5. It seems like a worthwhile swap (for the price of an extra on-on-on and a little extra stripboard).

Would you say that this tuned noise is also preferable to filtered noise for applications like keyboard control or LFO control? (As in would it be nice to keep both options for non-percussive purposes?)

Also curious if the double diode trick would be useful to the SN voice or more trouble than it's worth.

Thanks Thomas and looking forward to more cool stuff!

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Thomas_Henry



Joined: Jul 24, 2009
Posts: 129
Location: N. Mankato, MN

PostPosted: Tue May 22, 2012 1:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

I would stick with the 4046 noise clock. The sweep range is enormous compared to this new trick. The only advantage to this new circuit is that it uses far fewer parts. The trade-off is that the sweep isn't as large. But it still sounds damn good and the idea never seems to have been noticed before.

The double diode isn't required for the SN Voice since it brings the envelope out and provides a CV in for the sweep. In short, the SN Voice does everything and more, but is obviously more complex. The double diode is used here to ensure that sweep-up and sweep-down cover the same range, a non-issue for the SN Voice given its CV input structure.

This new circuit is more suited to a standalone drum box is my estimation.

And, yes, I've got new circuits coming out of my ears. I'll be passing them along to Scott for dispersal.

Thomas Henry
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jumunius



Joined: Apr 19, 2010
Posts: 346
Location: San Francisco, CA
Audio files: 13

PostPosted: Tue May 22, 2012 9:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Thomas, good to know. And certainly, its easier to just finish the SN Voice as is and build a separate tunable noise module!
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Tim Servo



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

PostPosted: Thu May 24, 2012 6:01 pm    Post subject: Tunable Noise Source Reply with quote  Mark this post and the followings unread

Hi Thomas,

Glad to see you back on E-M!


Tim (has also been called a noise source) Servo
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cheater



Joined: Aug 31, 2009
Posts: 1
Location: London

PostPosted: Sat Oct 06, 2012 4:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi guys,
has anyone ever posted any demos of this circuit?

If you have built this circuit, can you post some demos of it?

I have searched high and low and there's no audio of it.

Thanks!
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