Thursday, January 23, 2020

Ambient Arpeggios using LFOs and a Quantizer

One of the coolest things about Eurorack is that there are tons of neat tricks you can wire up with your modules, to produce some really cool sounds. 

A common trick, one that I recently came across, is the idea of using a LFO (low frequency oscillator) with a quantizer to produce an arpeggio. 

How exactly does this work? It's all in the quantizer, which takes incoming voltages from the LFO and adjusts them such that they match the voltage of a note that belongs to a scale (in accordance with the 1V/Oct Eurorack standard). That's why the outputted voltages (notes of the arpeggio) sound melodic, when connected to a voice. 

Here is a quick graph (not my graph) which should help visualize the concept of quantization.


As you can see, the blue line is the result of quantization; a discrete set of voltages, whereas the red line represents a LFO sine wave.

I decided to try out this trick by using Tides to generate some LFOs, 2HP Tune to quantize the notes and Rings to act as the voice. Here's the result:


Wow, Rings really does make some mystical sounds when you send an arpeggio into it, like the twinkling of a star! I love how melodic it sounds and the relaxing mood it puts you in.

Now let's break down this patch into a bit more detail. As I said, I've set up Tides to generate some LFOs. To do this, I've set the frequency range to 2Hz (yellow), the ramp mode to cyclic bipolar oscillations (red) and the output mode to different frequencies (red). That means that each output is producing a LFO of different frequency. Pamela's Workout is also clocking Tides.

The first Tides output is sent to Shades, to set the range of voltages. It is then sent to the Disting MkII, in full-wave rectifier mode, which takes the absolute value of the voltages (i.e. removes negative voltages). From here is goes through 2HP Tune, which quantizes the voltages to a melodic scale. As I mentioned above, this quantization creates the arpeggio of notes.

Rings is the voice of this patch. In particular, it's set to the quadriophonic (red) alternate "Karplusverb" reverb mode (flashing red) and receives the arpegggio sequence from Tune. This mode, I've found, is great for generating ambient-like sounds, mainly because of the reverb it creates. 

The other outputs of Tides are used for CV modulation, the second output modulating Rings' frequency setting and the third output modulating Rings' position setting. This adds a bit of dynamics to the patch, so it doesn't always sound the same.

The Doepfer LFO provides even more CV modulation, modifying the Tides' slope and frequency settings (this is what speeds up and slows down the rate of the arpeggio) as well as the brightness setting of Rings.

And finally, to add some randomness to the patch, 2HP TM generates a random voltage to set the bias of Tune. This modifies the base pitch of the arpeggio.


And that's pretty much it. It may sound a bit complex but the core idea of this patch, again, is passing a LFO through a quantizer to create the arpeggio of notes. Such a neat idea this is!

Have you tried out this trick? How did it sound for you? Let me know in the comments!


Happy patching friends,


-Uncle Peter

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