Intersecting Sequences

A signal gate is really just a fancy on/off switch — and an inspiring creative tool for modifying existing sequences and creating new ones.

A few years ago, I acquired an esoteric module for my old Roland modular synthesizer that contained four signal gates and some multiples. I knew what multiples were, but I initially had some head scratching as to the function of ‘signal gates’. After some brief testing it became apparent that ‘signal gate’ was just dorky parlance for an electronic switch; a signal connected to a signal gate is either output or muted depending upon whether it receives a (+/‑) voltage or zero volts. Essentially, it’s no more complicated than having a quartet of remote‑controlled light switches.

Within an hour it became clear that with just four of these very simple switches, an enormous number of things were possible and after trying a bunch of them out I was reminded of a linear drumming technique a friend of mine had shown me decades earlier. With linear drumming only one part of the kit is played on a given beat, meaning that it’s almost like switching through parts of the kit on a per‑step basis. Inspired by this, I set up four parallel sounds with associated sequences and connected them to the signal gates and then used a separate sequence to switch through the gates so that only one of the four sounded on a given step.

In essence, this approach brings a vertical sequencing element to an otherwise horizontal scenario, and before you start looking for a vintage signal gate module, fear not: this can be done with modern hardware alternatives and also in any DAW, free or otherwise, with just a mouse and some automation. Furthermore, it doesn’t need to involve synthesizers at all, the principle can be applied to any audio in general.

Picture 1: Four independently sequenced voices are routed through the signal gate before passing on to the mixer.

Firstly, let’s look at how this is setup with the original hardware, as shown in Picture 1. The user creates four complete voices that are being independently sequenced. These can be polyphonic, monophonic, simple or complex, it doesn’t matter. All that matters is that they’re sync’ed to the same clock source. I’ve used matching cable colours to make it easier to see, and voice 1 is purple, voice 2 is red, voice 3 is green and voice 4 is white.

In a normal setting, these voices would go to a mixer, but we’re going to add a signal gate/switch between each voice and the mixer. In the case of the 173 module, these switches are all conveniently next to one another, so it’s easy to see the connections.

Next, we need a four‑channel sequencer that is running in sync with the main sequences and that outputs gates. In my example, the first four drum gates from an Arturia KeyStep Pro do this job, with gate 1 connected to signal gate 1, gate 2 to signal gate 2, etc. I’ve used matching cable colours again to make this easier to follow, as you can see in Picture 2.

Picture 2: The Arturia KeyStep Pro sends four separate gate sequences to open the signal gate channels, allowing the sequenced voices to pass through.

In Practice

In our example (Figure 1) we have four 16‑step/one‑bar sequences that control different synthesizer voices that have different tonal qualities to them.

Figure 1: Four parallel sequences.

The sequences are numbered 1 to 4 and I’m going to call the sequence that switches between them the ‘Intersector Sequence’ to differentiate it.

Figure 2: An eighth‑note Intersector Sequence. The highest note is sequence 1, the next down is sequence 2, etc.

Starting simply, the Intersector Sequence (Figure 2) is playing constant eighth notes whilst stepping consecutively through sequences 1 to 4. The notes highlighted in red in Figure 3 show which parts of each sequence sound, with unhighlighted notes being muted. What’s interesting is that notes can become unmuted part way through sounding or be cut off before they’ve decayed.

Figure 3: Result of the eighth‑note Intersector Sequence.

The Cubase screenshot at the start of this article shows how this can be achieved with volume automation simulating the effect of the switching within a DAW without the need for a physical ‘signal gate’ module. For smoother transitions, softer automation can be used, but hard edits give an interesting choppy result.

Figure 4: Mixed‑value and non‑consecutive Intersector Sequence. The highest note is sequence 1, the next down is sequence 2, etc.

We can make this considerably more compelling by employing an Intersector Sequence that isn’t playing constant rhythmic values, but instead, a mix of note values (Figure 4). Plus, we don’t have to switch the sequences consecutively (1, 2, 3, 4); we can jump between them in any order. The result is what we can see in Figure 5.

Figure 5: Result of a mixed rhythmic value Intersector Sequence.

Better still, we can introduce polymeters by adjusting the length of the Intersector Sequence (Figure 6) so that it shifts against the sequences and creates different results with each repeat. The result is Figure 7.

Figure 6: Polymetric Intersector Sequence.

Figure 7: Result of polymetric Intersector Sequence over four bars.

Taking the polymeters further, we can adjust the lengths of the sequences themselves and use an Intersector Sequence that is a different length too (Figure 8). This exponentially expands the variation and means that repetition will only happen once in a blue moon. If any mathematicians want to work out the exact number of bars, let me know! The result is Figure 9.

Figure 8: Another polymetric Intersector Sequence. The highest note is sequence 1, etc.

Figure 9: The result of polymetric sequences and a polymetric Intersector Sequence.

To give this fuller context, Audio Clip 6 is Figure 9 with added drums, panning, reverb and delay.

From the same basic material we can easily create something short and repetitive, something long and complex with rare repetition, and everything in between.

Conclusions

We can see that from the same basic material we can easily create something short and repetitive, something long and complex with rare repetition, and everything in between. Better still, the variables that define the complexity are under the authorship of the musicians.

As mentioned earlier, this technique can be applied to any audio and not just synthesizers. For example, the same principle could be used with four rhythm guitar parts. The guitarist records four patterns that loop for the duration of a section of a song and then an Intersector Sequence can be applied to switch through the parts, creating a completely different guitar part altogether and one that’s much more engaging.

Or, the principle could be applied to effects sends, with one single instrument being continually switched between different effects, but rhythmically.

In fact, the number of things that can be switched is mind boggling, but the concept itself is very easy to understand and implement, and given that it makes us look cleverer than we actually are, what’s not to like?