Why is Bogaudio VCF output shape different than other VCFs?

Can someone explain why Bogaudio output shape is so different from other two VCFs?

I would guess that perhaps it’s because of the cutoff frequency that is set differently on it vs the two other. Bog’s cutoff appears to be just above 1 kHz, while the VCV filter is likely above 8 kHz in that setup (probably same for the Vult filter’s cutoff which is probably much higher than 1 kHz in that knob position).

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Sorry 'bout that. I forgot to turn it back up. Good guess but it’s still much different.

Look on a spectrum analyzer. Time domain view not so useful for filters.

Thanks for your reply. What am I looking for in the analyzer? Also, shouldn’t a sawtooth wave still be a sawtooth wave?

The BogAudio filter must be doing something different compared to the other filters that causes the time domain analysis to look different. Maybe it has a DC blocker or an additional “hidden” filter for very low frequencies.

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No, I’m not suspicious of bugs or anything like that at all and definitely don’t want to distract anyone there with my idiocy and was just genuinely curious and thinking I might learn something from understanding and nothing else.

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I only thought the VCF section of the manual is an interesting read and seems to confirm your observations!

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Ah haha yeah I did read that but went mostly over my head but I’ll read it again more carefully this time and maybe more will sink in the second time :grinning: Thanks!

Is there a particular part of that description that is the smoking gun? :stuck_out_tongue:

Yep the highpass filter :


Ah ha! Second-to-last sentence (lol was a good (re)read anyway lol):

“There is a fixed two-pole highpass filter on the filter output, at a cutoff of 80hz.”



All I’m seeing is that the Vult rolls off more at the top. There’s not enough detail in the analyzer plot to see the low freq stuff. You should use the ultra setting. Basically, the analyze shows what you hear. Looking at the scope you can’t really tell what something will sound like.