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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Calibrating oscillators without a scope
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dylar



Joined: Apr 25, 2011
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PostPosted: Mon Mar 19, 2012 10:48 am    Post subject: Calibrating oscillators without a scope Reply with quote  Mark this post and the followings unread

Is there any way to do this? I have Ray's 1V/octave keyboard controller, so I was wondering if I could calibrate the 1v/octave oscillator response this way:
1. Hook up oscillator to an amp
2. use a digital tuner (like a little hand held guitar tuner) to make sure that when I press the lowest C note on the keyboard controller the oscillator plays a C.
3. Press the next C key an octave up.
4. Adjust the trimmers until I get the correct response (oscillator plays a C note one octave higher).
I know this would not be as precise as calibrating the oscillators on a scope...but I don't have a scope. Will I get satisfactory results?
(P.S. - I'm shaping the waveforms using a software scope. I imagine this method is also highly suspect, but from what I can tell the wave shapes look okay.)
As an alternative: what is the cheapest oscilloscope I can get that will do what I need it to do?
thanks
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Blue Hell
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PostPosted: Mon Mar 19, 2012 12:12 pm    Post subject: Re: Calibrating oscillators without a scope Reply with quote  Mark this post and the followings unread

dylar wrote:
I know this would not be as precise as calibrating the oscillators on a scope...but I don't have a scope. Will I get satisfactory results?


Far better than with a scope ... unless you'd have an expensive scope with built-in in frequency measurement.

When I was at school in the late 70ties they'd teach me that a scope is not a measurements device ... things did change a bit with time, but basic usage of a scope is to judge waveform and not to measure frequency or amplitude accurately.

Another good way would be to do it by ear, also with far better accuracy than a cheap scope would offer.

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Uncle Krunkus
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PostPosted: Mon Mar 19, 2012 1:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, I second that.
If you can get your tuner to respond across a number of octaves, then that would be the best way to do it.
I sometimes use my DMM which has a frequency meter built in, but even that is not as accurate as a good tuner.

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Mongo1



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PostPosted: Mon Mar 19, 2012 2:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's what I did as well - I just used my CV based keyboard and a guitar tuner.

Gary
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roglok



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PostPosted: Mon Mar 19, 2012 4:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

The scope saved me some time during the initial CV scaling adjustment, but for fine tuning it's best to rely on a combination of guitar tuner/frequency counter and, of course, your ears.

Anyway, it's nice to see the scaling being reflected on the scope. It also helped me to understand the whole scaling/tuning process better. But as stated above, it's not essential.

For shaping the sinewave it's pretty handy too...
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dylar



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PostPosted: Mon Mar 19, 2012 5:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Excellent--thanks guys, you just made me feel a whole lot better.
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haxster



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PostPosted: Mon Mar 19, 2012 9:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you don't have a scope, google: musical tuner 1.2v, and also soundcard scope v1.4
Those are good enough. They will use your soundcard's audio Input
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dylar



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PostPosted: Mon Mar 19, 2012 10:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks--I used the tuner method and all the keys on the mini keyboard are now hitting dead on. Worked great and only took a few minutes.

Do software scopes actually work well enough for wave shaping? I tried one and it seemed to work but I'm suspicious. It seems like my audio interface regulates the signal at a max of 1V - if you turn up the input on the interface it just clips the wave, causing distortion. A real scope won't need to reduce the output voltage of the synth, right? (I've never used one so I don't know).

My sine wave is definitely messed up, but the square, triangle and ramp look good on the software scope.
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Mongo1



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PostPosted: Tue Mar 20, 2012 4:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Great! I'm glad you got it done.

Most conventional scope probes have a 10:1 attenuator and high-frequency compensation built in. I haven't used any of the software scopes, but I think they should probably be ok for audio frequencies.

Gary
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