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 Forum index » DIY Hardware and Software » Developers' Corner
Frequently Accurate Sine Waves?
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Stream Operator


Joined: Oct 13, 2007
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Location: near Austin, Tx, USA
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PostPosted: Wed Dec 28, 2016 12:52 am    Post subject: Frequently Accurate Sine Waves?
Subject description: ...with the emphasis on "Freq"...
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I have a really stupid question. I admit that I don't know much about oscillators. I just have a clunky non-expert sort of perspective on them so I'd appreciate someone's knowledge on this point. Also I think it is well known so I just don't know about it. It goes like this...

When you use a multimeter it's got like three maybe four digits of precision. Scope not so many either, function generator very accurate I suppose but it's a big clunky thing. When you look at a frequency meter, it tells you 100.000000... out the wazzooo with zeroes. The point I'm making i guess is that time is way more accurate than any other means of measurement.

So I think of our oscillators and I imagine... Why not make an oscillator with a time dependence. Something just a step up in complexity (a bit more complex unfortunately) from the basic oscillator that does the job very well. I can think of some circuits, but I'll just leave it at that for now...

If we begin with the premise of clocking our sine wave oscillator in some way, won't it naturally be astoundingly accurate? Like synthesis with a Karplus Strong thingie with a band pass circuit in the feedback loop? Am I just being stupid? Or uninformed?

Les

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Grumble



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PostPosted: Wed Dec 28, 2016 1:17 am    Post subject: Reply with quote  Mark this post and the followings unread

THIS is what I use as generator for sine, triangle and pulse generation, and sometimes as programmable clock generator e.g. for the filters I'm using in my diy synth.
These are very accurate to program in terms of frequency, very stable (since they are crystal controlled) wich is not always a good thing, because especially with sound you may want to have some beat to make it sound more alive, and if I want that I have to add it afterwards.
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Grumble



Joined: Nov 23, 2015
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Location: Netherlands
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PostPosted: Wed Dec 28, 2016 1:36 am    Post subject: Reply with quote  Mark this post and the followings unread

About measurements:
An analog scope is probably the least accurate instrument if you would want to measure amplitude, if you wat a accurate measurement for amplitudes, you need to have a digital oscilloscope, well at least it looks like it but....
The digital scopes in the diy segment all have an 8 bit adc, so only 256 values to measure a voltage (there are ways to improve on that but that would be too much to explain...)
Plus waht a digital scope can do what an analog can't is (the magig word in all of this:) AVERAGING!
And because of averaging the measurements of frequency seems to be so accurate.
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Stream Operator


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Location: near Austin, Tx, USA
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PostPosted: Wed Dec 28, 2016 1:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Attached is an image of the chip that Grumble uses. It is so accurate that it is too accurate for music (often) as Grumble tells us. That's awesome!

I'm thinking of something simpler, something like an oscillator that works on the principle of delay lines perhaps, sort of like a double Karplus Strong loop?

For example, how about a delay line that is RCRCRCRC - distributed delay line created by 3D printing layers of varying resistivity. Then a transistor amp at either end. Would that thing make accurate frequencies?

Les


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Grumble



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PostPosted: Wed Dec 28, 2016 2:00 am    Post subject: Reply with quote  Mark this post and the followings unread

To me this ^^^^ is simple Wink
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Stream Operator


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PostPosted: Wed Dec 28, 2016 3:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
To me this ^^^^ is simple Wink


Yes, simple to use it seems. Fairly complex internals though. Still, very nice!

Les

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