DivKid's Month Of Modular Issue #15 December 2016 - Page 7

This works, but the result can be a little random, with little control of what sequence comes out. Granted, much of the point of an algorithmic melody such as what this generates is this lack of control, but often we want to rein in this randomness, to better suit the mood we’re looking for. This month we’ll look at ways of shaping the patch to do just that.

What’s going on here?

To fully understand the possibilities that can be afforded by messing with the basic patch, it will help to get a good visual understanding of how the technique works. Those with descent experience in modular synthesis probably already have a good grasp of what’s going on, but let’s break it down and illustrate it for the newcomers. Figure 2 shows a simple sawtooth LFO at some frequency, and the vertical lines represent quarter-note divisions. The LFO is set to reset every whole note (at the bold line). The frequency of the LFO doesn’t match the tempo, but that’s perfectly fine, as long as the phase resets on each whole note.

Figure 2: A time-synced sawtooth LFO.

Now, let’s divide the vertical axis as well, with lines representing a scale: A pentatonic minor here, for sake of argument.

Figure 3: Preparing a quantier.

Finally, we trigger the quantizer on each quarter note. I don’t know if all quantizers use the same “rounding” function for their work, but let’s assume this quantizer simply ‘rounds down’ a voltage to the next lowest note. This gives us the red dots in Figure 4.

Figure 4: Quantizing on quarter notes.

The red notes now form a distinct pattern: D-A-E-E-D-A-E-E. And as you can see, as long as the LFO resets on each whole note, any repeating waveform will also give a repeating pattern.

Adding some spice

As you can see, as long as the LFO resets in time with the beat, any repeating waveform will give a repeating pattern. This implies that if we want to add some variation while we’re playing, we want ways of altering the LFO while keeping the tempo sync. Sounds easy enough.

Probably the most obvious way of altering the waveform is just to change its frequency. And sure enough, wiggling the LFO’s rate knob will give you a different pattern. However, there are a few drawbacks to this. First, lowering the LFO’s frequency to slower than the tempo will make it fail to complete a full cycle, as its phase is reset before it has a chance to do so.