A generative “Rack Metal” machine that spits out chunky, galloping heavy metal riffs.

This is a generative synthesizer patch but with a twist; it doesn’t sound anything like a synth, instead it emulates a heavy distorted palm muted guitar. It took some tweaking to get a ‘convincing’ guitar sound, but I think I got pretty close with 3 oscillators playing a power chord (root + 5th + oct) through a resonant LPF, then into a Fuzz module and a Cab Sim. But for heavy metal you need more than a heavy sound alone, and IMHO the key lies in the timing and rhythmic variations between palm-muted notes, open notes, and full-stops. So, this patch is based on a shift register sequencer that not only provides pitch info but mainly focuses on extracting rhythmic and timing variations from those shift registers. There are 4 different accents (double-tap, sustained note, full-stop, octave-up) that can be easily muted/dialled in to find the sweet spots in the stream of CV that the ever-evolving sequencer spits out. Oh, and it also provides a few accompanying trigger streams that could be used for kick/snare drum patterns, if you have a drum- or sampler-module handy.

I think this one worked out really well and it plays some pretty convincing chugga-chugga riffs. If you turn down the tempo and increase the decay it even does some neat doom metal! Obviously, I had a lot of fun playing around with this one. So, turn it on, set it loose, and embrace the riff. Once it gets going it’s damn hard to stop…

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[OVERVIEW]
-Input/Output: Stereo in/Stereo out (input just goes through dry)
-CPU load: Around 100%
-Build: Initial version built with firmware 2.80
-MIDI: All MIDI related modules (in PEACH colour) are on the 3rd page marked MIDI. I always use channel 10. If controls are set to CC’s I use CC channels 21/36 (see CONTROLS section for details).
-CV Inputs: Unused.
-CV Outputs:
1) Kick drum triggers.
2) Snare drum triggers.
3/4) Unused.

[REVISIONS]
1.0: Initial patch.

[CONTROLS]
All the main controls are on PAGE0 and PAGE1 and are labeled and starred (see below for a “Picture Manual” in the comments). The Stereo Output module with gain parameter is on PAGE2.

On first UI page:
EVOLVE (sets the chance that new CV/notes are injected)
BRUTAL (sets the amount of fuzziness and buzzing; lower values = tighter riffs)
SPREAD (sets the spread of note pitch)

2X (toggles the double-tap modifier on/off)
2X amount (sets the threshold for triggering double-taps)
2X shift (shifts the triggering of double-taps; 0-to-1 shifts from step 1 to step 5)

SUS (toggles the sustain modifier on/off)
SUS amount (sets the threshold for triggering sustained notes)
SUS shift (shifts the triggering of sustained notes; 0-to-1 shifts from step 1 to step 5)

REST (toggles the full-stop modifier on/off)
REST amount (sets the threshold for triggering full-stops)
REST shift (shifts the triggering of full-stops; 0-to-1 shifts from step 1 to step 5)

OCT (toggles the octave-up modifier on/off)
OCT amount (sets the threshold for triggering octave-up notes)
OCT shift (shifts the triggering of octave-up notes; 0-to-1 shifts from step 1 to step 5)

On the 2nd UI page:
6/8/10/12/14/16 (sets the sequence length; toggling between shorter and longer lengths can be used to creatively scramble existing riffs)
KEYBOARD (2 row on-screen chromatic keyboard that overdubs the generated riffs; can be used for melodic accents)

LPF (sets the depth of filter modulation for each hit)
LPF Q (set the resonance of the filter)
LFO (sets internal clock rate)
DECAY (sets the note decay; turn this up for slower tempos and doom-territories)
CLICKINESS (sets the amount of ‘picking strength’, emulated by a snappy pitch envelope for every hit)
HUMANIZE (sets the amount of randomization of a few parameters for each hit; filter depth, PWM)

On the IO page:
TUNING (set the general tuning of the oscillators)
MIDI CLOCK ON (toggles external MIDI clock)
MIDI PITCH DUB (toggles overdub function from external MIDI keyboard; notes are only dubbed if gate is high)

ZEBU LEFT button = Scroll through kick trigger patterns.
ZEBU RIGHT button = Scroll through snare trigger patterns.
ZOIA LEFT / MID / RIGHT stomp = Unused.

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[PATCH STRUCTURE]
The sound comes from 3 oscillators tuned to a ‘power chord’ (root + 5th + oct) and detuned by just a few cents. Two are sawtooths, but the 5th is a square (don’t ask me why but that sounded best), so lots of harmonic content for the filter and fuzz to chew on, and all oscillators have some mild pulse-width modulation to provide some dynamic overtone variation per step. Everything goes through a resonant LPF, then into a Fuzz module and a Cab Sim. The LPF is controlled via a snappy ADSR envelope, which is achieved by multiplying the ADSR output with itself via a multiplier. The decay can be set via the DECAY control on the UI pages, and it’s tweaked to offer short, muted power chord hits. I’m not using a VCA after the LPF, so the audio never closes completely (cause VERY low frequencies still go through the filter) which the Fuzz module loves because it can ring out quite a bit even after the envelope has closed. This is controlled with the BRUTAL setting; set it high enough and there will never be silence – as it should be!

The sequencer is a basic Turing machine; a chain of 16 shift registers (=Sample&Hold modules), that can continuously evolve or be locked into place (via the EVOLVE setting). The first S&H is multiplied with itself to provide pitch information (by making it exponential you get much more root notes than higher ones, so more ‘realistic’ for metal riffs).

Then there are the Four Modifiers Of The Apocalype(!!), which are taken from one of the first five S&H modules via the SHIFT setting:
0.0-0.2 -> S&H1
0.2-0.4 -> S&H2
0.4-0.6 -> S&H3
0.6-0.8 -> S&H4
0.8-1.0 -> S&H5
The selected S&H is sent to a Comparator to determine if it ‘triggers’ the modifier, the sensitivity is set via AMOUNT (so at 0 there are none, same as muted, but at 1 it’s constantly firing that particular modifier). The modifiers have a kind-of priority over one another; if a DOUBLE-TAP is triggered but at the same time a SUSTAINED note occurs, it will sustain the note. In the same way REST modifiers take priority over DOUBLE-TAP and SUSTAIN. OCTAVE-UP can occur simultaneous with the other effects so no priority needed there. Because of this prioritization you can easily crank the DOUBLE-TAP amount while still keeping the rhythm interesting with stops and sustains, but if you then mute those it will switch to a galloping double-time break. So be creative!

Long technical story but to summarize; by setting different SHIFT values for different modifiers, you get differences in timing of the effects and by setting different AMOUNT values you get differences in occurrences of the effects, and even if modifiers overlap they take priority over one another in fun ways.

Okay, finally there’s 2 CV outputs for accompanying drum triggers. The most basic patterns are kick-snare-kick-snare, but you can get some variations via the KICK PTN and SNARE PTN buttons (on ZEBU only). The kick takes its additional trigs from the modifiers, so it aligns nicely with the riffs being generated. I started with some half-decent sounding drums built into the patch itself, but due to CPU shortage I unfortunately had to take it all out in the end.

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[TIPS/TRICKS]
>>> Set tempo to about 140-160, increase EVOLVE and wait until you hear something you like, then turn that to 0 to ‘lock in’ the riff. Now, just play with the modifiers and bang your head!
>>> This patch really wants ‘to be played’, so use the built-in keyboard to place melodic accents and use those MUTE/UNMUTE buttons until you’re screaming ANGEL OF DEATH!!
>>> Slow the tempo to about 30-40 and crank the decay for some Doom and despair. And turn up BRUTAL for that non-stop buzzing bass sound!

[THOUGHTS/IDEAS/PLANS]
This patch is done for now, but I’ve already had so much fun with it even before it was finished, so I have a feeling I might change/add some things or maybe evolve this into some other patch(es) in the future; it’s just very musical and – even aside from the heavy metal aspect – has a lot of cool patching techniques I think.

If there’s any bugs/questions/remarks/requests or suggestions for improvement, please let me know!
Enjoy!

(Image: Tom Hegen)