Tune Up, Fade In, Jam Out: Advanced Oscillator Tricks

May 15, 2013
In the previous column, we started tuning oscillators in various intervals. This month let’s have some fun with bringing in transposed oscillators using a performance controller. In today’s world of soft synths, oscillator mixing is not as commonly thought of a “knob assignment destination” as, say, filter cutoff or envelope release. On analog synths like the Minimoog, though, those knobs were right there in your face, encouraging realtime tweaking. Bringing tuned intervals in and out freely, at choice spots in your solo, is a very nice way to add variety to your synth leads.
Click thumbnails for larger images below.

Fig. 1. Rob Papen Predator offers level control per oscillator. In the circled area, a modulation matrix slot is used to tie oscillator 2’s output to a foot pedal.

Fig. 2. The center area of Novation V-Station is the oscillator level mixer, which we have a dialog open to modulate.


Fig. 3. Modulating the mixer knob for oscillator 3 using a foot pedal in the matrix (top area) of Gforce Minimonsta.


Fig. 4. On most Korg workstations, each oscillator has its own filter path, so the output levels are in the filter section.

Fig. 5. A matrix setup to bring the main layer down and the tuned-interval layer up using a single controller, in Spectrasonics Omnisphere.


Fig. 6. Dialogues open for this same technique in Applied Acoustics Ultra Analog.



Where are the Levels?

Right off the bat, I need to point out that not all synths and soft synths can do this technique as part of their voice architecture. You don’t just need knobs to control the levels of each oscillator—you need the ability to modulate each of those knobs independently. In researching this column I found a number of soft synths that don’t provide this. Here’s a plea to synth designers to build this in via a modulation matrix, or mixer design of some sort. True, you could still MIDI map knobs on your controller directly to oscillator levels, but since this normally isn’t saved per patch (unless you want to get into programming and saving presets on your MIDI controller), it ties up those knobs for all your sounds. So, where do we find the level controls on soft synths that can modulate them?

In the oscillators themselves. Rob Papen’s Predator, for example, is organized this way. With the abundant slots in the modulation matrix, you can bring in a second oscillator or even cross-fade oscillators all under the control of a single modulator. In the circled area of Figure 1, a foot controller (CC 04) is bringing up the level of oscillator 2 (Mod 2), which we’ve pre-tuned a fourth down. Oscillators 1 and 3 are providing the same base pitch, but they’re slightly detuned to produce a nice, fat sound. Don’t be confused by the fact that oscillator 2 shows a given level set as a default—it’s set that way to produce a smoother response from the pedal, so the oscillator comes in faster, earlier, or more smoothly. With your pedal heel to the floor (minimum) the oscillator level is -40dB, which can’t be heard alongside the other two oscillators. 

In a mixer section. Taking after the Minimoog, many soft synths use a mixer instead of putting oscillator level knobs in the oscillator sections themselves. Can the mixer levels be modulated? If they don’t seem to be onscreen, remember that we can likely do this via MIDI Learn. In Figure 2, I have set up the same type of sound in Novation’s V-Station and then used the automation feature in my host (Apple Logic Pro in this case) to control the mixer level of oscillator 3. If you play a hardware Minimoog or Little Phatty, you could just reach for the mixer knob when you want to bring in the tuned oscillator. The best software virtualizations add more advanced capabilities, so I can do this easily in Gforce Minimonsta (Figure 3), or Arturia Mini V, thanks to their modulation matrices.

In the filter? Yes—there might be an output level for the filter that can be modulated. This is how most of the oscillator on/off and fading is programmed in Korg’s M3, M50, OASYS, Kronos, and Krome keyboards (Figure 4). This only works if each oscillator has its own filter path; if all your oscillators go into the same filter, you’ll need to use one of the other techniques.

Filter fake-out. If you do have separate filters, but the filter output isn’t available as a modulation destination, the filter cutoff can fake oscillator level control. The idea is that a completely closed lowpass filter will pass no signal, so it’s like the sound is turned off. As you open the filter you start to hear the sound, and the amount you modulate this will bring your sound to the desired “level” you want, based on brightness. I wouldn’t use much (if any) filter resonance when doing this, as you simply want to hear the tuned oscillator come in, not have its frequencies swept with any character.

Once you’ve found how your hardware or soft synth modulates oscillator outputs, try it and practice incorporating it into your playing. One technique I like is to play a phrase “plain” and then play it again with the added tuned interval. It’s like a call-and-response between two players. It also works well to change octaves for one of the phrases; try playing the “plain” version down low and then answer it an octave higher with the added interval.

Fade to Feedback

Taking the concept a step further, you can fade out your primary oscillator(s) as you bring in the tuned interval. Among other cool uses for this, it’s key to simulating the sound of guitar feedback. For performance reasons, you want to do both fades using the same physical control. So, whatever controller you’re using to fade in the transposed oscillator, it needs to be assigned to control the level of the primary oscillator(s) as well, but in reverse fashion. 

If your soft synth has a modulation matrix, this should be easy. You simply assign the same controller to the desired parameter (oscillator level, mixer level, filter output, etc.) but with a negative modulation value. Figure 5 shows a setup in Spectrasonics Omnisphere, using CC 02 (breath controller) to fade out layer A by inverting the modulation value, while fading in layer B.

With MIDI learn, this may be more difficult, as some synths don’t allow the inverting of the modulation range, or the same controller being assigned to two different destinations with an inverse response to one of them. One synth that does allow this is Applied Acoustics Ultra Analog, and Figure 6 shows the setup that makes this happen.

Oh, and let’s not forget to tune the second (or third) oscillator to a higher pitch. Common choices are an octave higher (+12 steps) or an octave and a fifth (+19 steps). Add a touch of delayed LFO vibrato and you’ll be on your way. Since feedback is a very pure sound harmonically, you can use a simple sine wave for the tuned oscillator, but that’s not a hard rule. Do what sounds good to you. Until next month, happy soloing!

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