korg nuvibe lfo (sliders/ waveshaping)

[nepalnt21]

seems to me that the korg nuvibe takes over where other vibe type pedals leave off... i mean, you can make a phase 90 sound pretty darned close, but the waveshape of the lfo... that's not something that all uni-vibe like pedals can do up proper.

now having an array of sliders which allows one to choose the shape, that is genius to me. and having done a lot of work on DAWs, i think the interface would be quite easy to use.
apparently it is a bunch of fets, being used as variable resistors? that could make sense, except how to smooth the edges? (in digital sound processing, i believe the process is "interpolation"; is there a similar process for analog circuits? i understand that if i were to use big caps to smooth edges, only some of the edges would smooth?

anyway, really i'm wondering if anyone has ideas, or literature on how to go about this, cause none of my combinations of search terms generate any hits. i really want to figure this out.

blathering over

thanks

[Mark Hammer]

The sliders are basically a sequencer, used to produce a waveform (10 steps?  hmmm, can you say CD4017?).  Most sequencers will incorporate an adjustable smoothing-vs-stepping feature, roughly identical to the "portamento" of a synth keyboard.  I'm not all that familiar with the Nu-vibe, but I gather the objective is to produce waveforms that could mimic bulbs and LDRs with various rise and fall times, in addition to being able to set the sweep width, and general range where the sweep occurs.  In which case, I gather the unit does NOT use bulbs and LDRs itself, but some other control element.  I can't see a sequencer being able to exert much control over an incandescent bulb.

[PRR]

> I can't see a sequencer being able to exert much control over an incandescent bulb.

It's slow, which restricts how fast it can change.

But theatrical lighting designers do/did amazing things with sequencers and incandescents (now going LED arrays). Since before the dawn of memory lighting boards, theatrical lighting is all a "sequence" of "scenes" with each lamp playing its light/dim/dark role. Not on a fixed clock, because actors are inconsistent, but in the simplest cases the light board operator just presses a GO button to step the sequence along.

Recently I saw a 1959(?) ad for a 40-knob arbitrary waveform generator. But human interface aside, these days you would use a chip.

[Mark Hammer]

Agreed.  If we're talking theatrical lighting changes, where fades are acceptable, a sequencer controlling light intensity (indirectly, of course, through triacs or similar) has no timing-incompatibility issues.  In this application, where a 2hz modulation rate, using a 10-step sequencer, makes each step equal to a 20th of a second (50msec), an incandescent bulb would be too slow to respond.  One would be on to the next step before the bulb had a chance for the filament to cool off.  I have only seen a passing gutshot in the interview video with the designer from Korg, but it doesn't look like there are any bulbs in it.  As for "76 transistors", a chunk of those are likely dedicated to illuminating the sliders, and not for any sort of audio path tasks.

[ElectricDruid]

47K input impedance, 20K output impedance. Ouch.

If it was me trying to smooth the output from the 10-step sequencer, I'd use an op-amp integrator stage:

https://www.electronics-tutorials.ws/opamp/opamp_6.html

This is the typical "portamento" circuit from synths that Mark mentioned. Depending on how wide the LFO range is, you could either set a fixed amount of smoothing (in which case, higher frequency LFO waves would be smoothed more and would be reduced in amplitude - this might well be exactly what you need to prevent vibrato getting deeper as you increase the LFO rate) or you could provide some kind of tracking so that the smoothing follows the LFO rate (VCA-controlled integrators are a standard part of many synth filters, so this is well-proven tech).

HTH,
Tom

[nepalnt21]

thanks for the replies! three of the greats in my own thread? im honored   

i had already looked into the 4017 on a tip from the only other korg nuvibe thread i could find, but this is still so new to me, i think it was over my head.

of course, the glide function! i was looking at step sequencers thinking "cool, but not what i need", not even considering a portamento function. i needed that reminder, thanks mark and tom for that! (i think i know it as "glide", if that is the same thing)

[Mark Hammer]

Yup, "glide" and "portamento" are, in practice, at least, the same thing; the one term being a little more self-evident than the other.

A listen to the the various Youtube demos indicates that different feels are available via the 10-step waveshaping.  While lit sliders are not necessary for that, they help the user to conceptualize how waveshape affects feel.

[ElectricDruid]

Important question: Does it do the Knightrider thing with the LEDs when you turn it on? 

[nepalnt21]

i didn't know this, but fumio meida, inventor of the uni-vibe was also the head of the korg nuvibe project.

according to this interview

https://www.youtube.com/watch?v=o1WGjQtU3CU

also, for the original effects (psychedelic machine, vibra chorus, and uni-vibe) apparently he wasn't going for a rotating speaker effect, but the sound of a.m. radio propaganda broadcasts from u.s.s.r. interacting with the ionosphere.