Spectrum analysys - extra harmonics - phase reset in oscillators

Hi everybody, I’m new here and just a beginner of vcv so i do apologize in advance wether my doubts sound silly to you.

I am putting a lot of efforts in studying electronic music and modular synthesizers in general and I’m trying to build different circuits in order to test basic principles and behaviors of modules.

So far I found 2 unexpected results:

1_Checking the spectrum (with a Bogaudio’s analyzer) of a standard sine wave, I discover it has more than 1 harmonic. I thought it was due to an impure sine wave create by the module (standard VCO-1) but, after checking its shape with the scope, it resulted to be a pure sine.

2_Testing the behavior of any couple of VCOs working together, before and after applying any modulation (sync, fm or even just frequency’s change), I am not able to restore the result just by removing the modulation and I need to restart vcv. Ex. Plugging two VCOs, saw and inverted saw, into a mixer I obtain, as expected, an attenuated signal. The result changes whilst changing parameters but I need to restart VCV in order to regain the initial result (i.e. attenuated signal).

thanks in advance

For the 1 : Additional harmonics are generated from the VCO-1 even in the sine mode. It doesn’t generate a perfect sine wave. The sines (both from the digital and analog modes) will look very much like sines on the scope, though. (You can notice a tiny difference in the shape when you switch between the analog and digital modes.) A very small change in the waveform compared to a “perfect sine” can produce a “big” change in the frequency analysis, especially if you look at the spectrum with the extended amplitude range.

The 2 probably has to do with things not being resetted when you might expect them to do so.

There is a difference in the digital/analogue sine.(switch on the left)

And you can reset any knob to its default state by doubleclicking it.


Thank you guys: really helpful and kind. But I still have the same problem with topic _2

This is the result before applying any modulation

This is the result after changing VOC-1’s frequency

Final result after restoring frequency to its initial value

The oscillators are “free running”, once you change the frequency, you can get back to the original phase only by luck, if the oscillator doesn’t have a phase reset function. (The sync input in VCO-1 might work for that…)

Real analog taste then :wink: I tried with sync and everything works properly. Thank you very much for your support

It does, and it works ( use bog manual )

I use sum (1 too many) to compensate for the 1 sample per module delay.

As people have said, the “Analog” sine has intentional distortion in it. If you want to get really lost, set the Analyzer for “ultra” Quality and set the Amplitude Plot to 120 dB. Now compare all the sines you have access to. They will have different minute distortions. I don’t think anyone case hear these minute distortions. If you are very curious, try my “Basic VCO”. It has two sine also, one having much less low level distortion. But, as I say, I don’t think this is audible.

Really thank you very much… my way is to dive into things and, since I am studying from a really professional book, I got confused because the author didn’t mention about that extra harmonics (I am actually just at the beginning of the book :wink: )

I also tried your VCOs and I discovered they produce less “extra harmonics” even with an extended sensitivity as you suggested.

Thank you very much

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If your are ever in the mood for an obsessive dive into VCOs, I have this repo called “Demo”. It a bunch of VCOs showing the various problems that typically occur and how to avoid them. This “demo” VCO did eventually become my “BasicVCO” and “Organ-3” modules. There’s a lot here about using the Bogaudio analyzer, too. https://github.com/squinkylabs/Demo

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More than obsessive… I would say almost masochist I will have a look at your demo and let you know :wink:

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Welcome to the forum Antonio. I edited the title according to what came out in the discussion.

Reminder to everybody that you can and should edit your posts, including the title and the forum category, even after you’ve published them. Detailed titles even if a bit long are appreciated.


Thanks for the welcome, I am glad to be part of this community since it seems I’m finding great competence and willingness.

Sorry for the confusion with the title but I was not sure how to name my post but, at the end, simplicity always wins…

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