Deeper Inside the Rudess Synth Lead Sound

November 15, 2013
Last month we began exploring Jordan Rudess’ signature lead sound for his Korg Kronos. We covered the basic lead tone, its effects and controllers. Now it’s time to explore how he simulates feedback harmonics and some other cool variations he can draw upon during performance. Scroll down for audio examples.
Bring On the Feedback

As we covered in the April 2013 column, you need to fade out the main oscillator(s) when you want to simulate feedback, and Jordan does this using an effect rather than modulating the amp output. Why? I’ll explain a little later. Using two Stereo Limiters he has one set to cut the volume when pushing the joystick up (JS+Y) and another to cut the level when pulling the joystick towards you (JS-Y). This is done by modulating the gain stage within the limiter negatively when the controller is moved. Either way you push the joystick, the main sound fades out, leaving room for the feedback tones.

The basic tone of the feedback is produced by an AL-1 program with a pulse wave set to 50 percent width, tuned up an octave and a fifth. This is a nice, hollow sound—perfect for simulating feedback, and a bit stronger than using a sine wave. That oscillator produces no sound when a key is depressed; only the movement of the JS+Y raises its amp output. A second oscillator is set to the same waveform but is only tuned up an octave, so it sounds below the main pitch and only comes in via pressure, so you can sweep into the feedback using the joystick, and then slowly add the additional harmonic using aftertouch as you wish. Nice!

Even hipper, Jordan Rudess uses the ribbon to introduce some ring modulation to the sound, with a setting called AM—which is the traditional ring modulation between the two oscillators plus the original carrier wave’s dry signal mixed back in. Listen to it being demonstrated online; it’s a cool extra bit of “drama” added to the sound. Remember that the ribbon added a sub-oscillator to the regular sound, which goes away when the harmonics are introduced, so he reuses the ribbon for this coloration.

The feedback shares the same spiked amp envelope for that punchy attack, and nothing special is happening for the filter, since he wants the sound to remain pure and open the whole time. A second instance of the AL-1 (the Kronos can stack two sound engines, either different or the same, in a single Program) uses similar settings, and is brought in via the JS-Y movement. Here the main oscillator is tuned up two octaves, with the pressure-induced second oscillator tuned up only one octave. The ribbon again introduces the ultra-cool AM ring modulation. 


Fig. 1. The effects chain for the main lead sound.

Fig. 2. The effects chain for the feedback sound. Fig. 3. Using the Kronos’ secondary (vector) joystick to bring in an extra sync sound.

Whole Lotta Oscillatin’ Goin’ On!

The benefit of using separate programs is becoming apparent, as Jordan is using a lot of oscillators to produce the cool variations in the sound, and no single program would offer that many resources. But playing this sound on an 88-note keyboard introduces another issue that’s solved by using multiple programs. As Jordan moves far up and down the keyboard, the feedback tone moves out of its “sweet spot,” so he uses multiple copies of the sound and shifts their pitch so they repeat halfway across the range. The upper end of the keyboard is tuned an octave down, and covers notes G#4 to G9. The middle of the keyboard is set to “zero” tuning, and covers G4 down to E3, effectively repeating the same pitches. A third copy of the program is set to play from D#3 down to the bottom with the same tuning, but with a much lower volume in the mix, taming its output when he wants to go way low.

Let’s tally up the total oscillators involved here: The main sound uses two detuned oscillators, with a third one acting as a sub-oscillator, or simply tuned down an octave. The feedback Program uses two oscillators for the JS+Y/aftertouch sound, and another two for the JS-Y/aftertouch sound, so we’re up to seven oscillators. The repeated copies of the feedback each use two oscillators (two times three instances equals six), so in total we have 13 oscillators in action!

Routing Rules

Another benefit of creating this sound in a Combi (a multi-sound stack that might be known as a Performance, Multi, or Setup on synths other than the Korg Kronos) is for flexible effects routing. Very few synths offer the ability to route each oscillator to its own effects chain. Since Jordan is using the Kronos’ Stereo Limiter effects to fade out the main sound, he needs to be able to route different parts into different effects. So, the feedback tone doesn’t go through those limiters. He runs the feedback tone into a Tube PreAmp Model (within the Kronos) for some extra warmth before it “joins” the rest of the amp/distortion chain (see Figure 1).

Wait, There’s More!

To bring even more performance variation into the sound, Jordan uses a knob to turn off both the Limiter’s gain reduction when using the joystick’s Y-axis (the knob sets each limiter’s mix to dry, bypassing it), and brings in a second distortion effect—this time an Overdrive with a built-in wah (see Figure 2). The effect isn’t adding a lot more overdrive; he uses it for the wah component, sweeping the wah open as he pulls the joystick towards him. So at certain points in his solo he can abandon the feedback tones and revel in the wah and the nearby sub0oscillator (via the ribbon).

This explains why he used Limiters to fade out the main tone; if he’d done it via amp modulation at the oscillator level (as I taught you earlier) he couldn’t easily switch that off when he wanted to reuse the joystick to become the wah controller. Could he have left the joystick to fade out oscillators and used a pedal for the wah sweeping? Sure, but as he stands as he plays and likes to swivel his keyboard around for dramatic effect. So, also trying to operate a pedal might have made for some awkward stage poses.

Hidden Treasure

As I explored the sound I found one other cool programming trick that was in the main lead program, which Jordan had disabled in the Combi. When I asked him about it, he confirmed that since it used the rather small, secondary vector joystick on the Kronos he abandoned it for live gigs, as he found it too hard to use the small stick effectively in the heat of performance. However, this speaks to the principles this column has been all about—introducing more timbral variation during your solos—so Jordan agreed that we should share it.

In the main lead sound Program he used the vector joystick to fade out the main AL-1 program, using amp level modulation. At the same time he faded in a second instance of the AL-1, set to a similar sound, but also using oscillator sync to add more edge (the slaved oscillator was tuned down an octave, and the master oscillator is tuned up three octaves and a fourth). This main sync sound is produced when moving the vector joystick up and away from you (VJS+Y). Moving it down and towards you (VJS-Y) brings up the same sync program but also retunes the second oscillator to another pitch and introduces a slight amount of FM. This gives you plenty of diverse timbral variation via the controller. Listen to the audio examples below to hear the cool tones it produces.

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