From the course: Learning Modular Synthesis: Eurorack Expansion

Verbos Complex Oscillator: FM (frequency modulation)

From the course: Learning Modular Synthesis: Eurorack Expansion

Verbos Complex Oscillator: FM (frequency modulation)

(electronic tune) - [Narrator] Now the real fun comes in when you use this modulation oscillator to start bending what's happening with the master oscillator. I'm going to simplify things here just a little bit of wave folding. (electronic tune) There we go. Now initially, I could use the modulation section just as a low frequency oscillator to change the amplitude or the pitch of the sound to get tremolo and vibrato. Go to amplitude modulation. (electronic tone) Increase the modulation index. (electronic tune) Or frequency modulation, just to get a little bit of a pitch warble. (electronic tune) Now, something interesting about the modulation oscillator in the Verbos is it only puts out positive voltages. Everything is unipolar. Let's go ahead and look at, say for example, it's triangle wave. It's going at a very low frequency, but as I dial it up, you can see there just exists above the waveform on the master oscillator. Same for the square, same for the saw-tooth. Go back down to a slow pitch warble. A consequence of this being just a positive going waveform is that it only shifts the frequency upward and it only opens up the amplitude in a positive direction. Since the frequency modulation on the Verbos is internal buzz, it's exponential. That means once you set a musical interval or vibrato, it will stay the same as you play up and down the keyboard. The side effect is though it means that the frequency modulation effects are a bit more aggressive. The positive nature of the modulating waveforms also has some implications when we start enveloping its amount, and I'll show you that later. Now where things get more interesting is when this modulation oscillator is pushed up into the audio range. Then a new harmonics are created. (electronic tune) Now right now it's staying on the same pitch, so when I go off to see that tune things too, (electronic tune) things go out of tune. So I'm going to need to make it track my keyboard as well. I could just take an outfit from my buffered molt, go into the volt octave input, and retune this, or I could go ahead and put it through something like precision adder to quickly change to different octaves. (electronic tune) We'll keep it simple for now and just direct connect it. That creates a nice, fat sound on the base. Remove the envelope from the wave folder, increase the modulation index, notice that the pitch shifted upward as we changed the modulation index. As a consequence of this voltage being positive going, it's average is going to be positive, so therefore we're going to have a positive shift in the pitch. (electronic tune) And again, we can further change the output with the wave folder section. Oh, now that's a rich sound. Little bit of enveloping to the wave folder. (electronic tune) Little extra attack there. Again, things get more interesting when we envelope depths of modulation or depths of change to our timbre. This case, we can go ahead and envelope the depth of that modulation index. Turn that down, steal my envelope from my wave shaper, this is where you need even more envelopes. Put it into the modulation input, and start raising the amount that's being let through as this envelope opens and closes. (electronic tones) I'll go to a sor-deh-cay just so we can hear it. (electronic tones) I'll increase the modulation index so even when the decay has gone all the way down to zero, this is staying level, we'll still have some kind of modulation going on. (electronic tones) And different wave shapes will produce different changes in the wave form and different harmonics. (electronic tune) Now that is an interesting sound with a very complex attack, it would be good for percussion, things like that. However, that pitch shift during the envelope of the modulation index does make it harder to use in some melodic sets. We can bring in another oscillator, such as the Moog's own oscillator, into the linear FM input. And use something that's maybe a little bit more powerful a bit more on pitch. Linear FM tends to stay more tonal, doesn't as much problems with pitch shifting. And the Moog's oscillators are bounced around zero volts. Let's go ahead and bring that in briefly. I'm going to pull the modulation for now, so you can hear what's going on more clearly. Turn down the modulation index. (electronic tone) You hear that, what that pitch shift is like. Grab the saw-tooth output from the Moog's own oscillator, which looks like this by the way, that pink wave shape. And feed that into the FM input, for our master oscillator. Increase the FM depth, get a richer sound, tune them together. (electronic tune) Nice sound that does not shift as much in pitch as I change the index, just changes the timbre. Now if I want to actually envelope that, like I was doing here with modulation index, I would need to take it through our external VCA. Well, we can do that, so go ahead and take that saw-tooth, audio this point, put it to the input to my VCA, take the output of the VCA to the FM input on that oscillator, then we'll take this modulation source and make that my control voltage. So we can go ahead and either just manually open up the VCA, turn down the CV mod for now. Modulation, or envelope it. (electronic tune) So even though you have a complex oscillator, you're not locked into using just it to modulate itself. It usually has inputs, so you can bring in outside sources. In this case, I happen to personally like the sound of taking the Moog's bipolar balance oscillator into the linear FM input on the Verbos.

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