I modeled guitar pedals in Serum 2's FX rack - here's how (Lab Notes #3)
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Serum 2 is by far my favorite synthesizer, as you can see from our catalog of Noise Department products, but Serum 2 is missing something important that its rival Phase Plant already has.
You see, Kilohearts offers two modules called Snap Heap and Multipass, both of which allow you to bundle a bunch of effects together into a nice self-contained unit. When you’re inside Phase Plant, you can load up one of these modules and select a preset, and it just looks like a single effect in your chain with a couple of knobs, but it’s really any number of effects just abstracted away from your view.
Serum 2, unfortunately, doesn’t have anything like that. You get three effects lanes and there’s a few parallel splitters but everything sort of lives on the top level. A sneaky side effect of this is that designers like myself won’t even make an attempt to create abstractions.
The workflow is usually:
1) mess around on the oscillator page,
2) lfo and envelope stuff,
3) make it sound cooler by adding effects from the dropdown. Add a distortion, add a reverb, add an OTT.
Okay done. Save it.
But all last year I couldn’t help but think that serum’s lack of abstraction tools like snap heap was causing me to miss out on an entire category of sound design. The kind where the effects you use define the flavor of the end result far more than the source material does.
Take the BOSS Heavy Metal pedal for example. Everything you run through it sounds like the heavy metal pedal. It’s not enhancing the sound, it’s redefining the sound.
And what’s inside that pedal? Well there’s diodes and filters and EQ stuff at the very least. You could say a guitar pedal is an abstraction, it’s the physical equivalent of Snap Heap.
Serum has been and probably will be one of the most popular softsynths of all time and it’s already very good at like 99% of synth related things. But that last 1%, the missing abstraction stuff, is a very big 1%.
In the rest of this post I’m going to show you how I overcame that limitation and gave Serum the power of guitar pedal distortion using it’s own internal effects.
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Consider Serum’s FX page. The devices are single-purpose and modular. The chorus is just that. The compressor just compresses. The distortion effect distorts, and you get to choose from one of a number of flavors. Tube, linear fold, tape, etc.
What Serum doesn't tell you, though, is that all of those effects are like parts of a car. What you really want is to build the whole car, but each instance of distortion, eq, filtering, etc. is like one wheel, one mirror, one headlight. To build the car, you need to combine all the parts together into a car shape.
Just to hammer it home, the distortion options Serum gives you are atomic, singular distortion stages. One diode, one tube, one soft clipper... not unlike the individual components of a circuit.
Let’s jump out of Serum briefly and look at a circuit diagram of a simple guitar pedal, like the Ibanez TS9 tube screamer. I know it's hieroglyphics to many of you, but the takeaway is that not only is there a distortion stage, but there’s stuff happening before and after and after that distortion stage.
For example, this ElectroSmash article writes:
“Harmonics above 720Hz get the full gain of the distortion stage, and everything below it gets progressively less gain and distortion. Bass notes are clipped least, so the distortion is frequency selective.”
In Serum’s distortion module, you can apply a pre-distortion high pass filter, but its pretty crude and I prefer to use either a dedicated EQ module so I can do something drastic, or if I want to go very subtle, perhaps I’ll use the 6db per octave Filter module. Either way, you now have much more control over what parts of the sound are distorted.
If I were to try to build a full effects chain which sounds like a guitar pedal, I’ll need to start adding effects modules in the spirit of a circuit diagram. That is to say, I'll need to add a lot of stuff.
As I kept adding devices, I was continuously checking how the waveform looked if I ran a sine wave through it. In addition, if I own the guitar pedal, I'd be constantly checking how the sound and the waveform compared using an A/B splitter rack in Ableton Live.
The more time I spent trying to match guitar pedal sounds in Serum, the more I began to notice fundamental differences between audio processing in serum-land vs real-electricity-land.
First of all, the biggest challenge was managing gain staging inside of Serum. The dynamic range of audio would be squashed flat so quickly that it pushed Serum into sounding artificial and "rigid" compared to what the hardware would do. It took a lot of effort and a lot of utility devices to open up that range in a satisfying way.
The second biggest challenge was about biasing. In other words, asymmetric clipping, where one side of the signal is distorted more than the other. You see, Serum's X-Shaper is very flexible but it quietly applies a DC offset filter immediately after the wave shaping happens. This is great for casual use when you don't want to worry about that stuff, but when designing distortion chains it ruins any chance of carrying that asymmetry further down the line to be processed by other stuff. There's no way to remove or disable the filter, but some extremely pixel-perfect X-Shaper curves can get you to a result that sounds decent enough to forget about it.
Lastly, it's well-known that a lot of analog gear will handle sudden transients in a sluggish or otherwise non-linear fashion. Transients being big spikes in volume, drum hits, etc. This property of the devices was nearly impossible to model in Serum, but by using more wave shapers, compressors, or a combination of both, I clawed my way up to a "passable" emulation of that behavior. At the end of the day, my goal wasn't to nail it exactly because that would be unrealistic, but I did want to make sure they sound tasty on everything from drums to synths to vocals and more.
So let’s say I like the sound of a rack and I want to save it. There’s no module like Snap Heap, but what Serum does have is FX rack presets. I can click the disk icon, save the rack, and then if I want to recall that bundle of effects I can do that. It’s a bummer that it eats an entire effects bus but we made a full pack of presets for Noise Department using these racks and it really didn’t cause too much of an issue.
In fact, at the end of this process I ended up with 12 different fx rack distortion presets, 7 of which were modeled after physical units that are sitting right next to me on my desk.
To get more of a snap heap experience, I set up serum to load the effects busses in series by default instead of parallel. In bus 1 I do any of my pre-distortion stuff, and in the main bus I do all of my post distortion stuff, leaving bus 2 as the place where I flip through fx rack presets.
Put all of those things together and you end up with a very mean-sounding serum.
You might still be asking “why not just use the real pedals? Why bother doing all this in Serum?” and the first answer is: workflow. Turns out, at least for sound design anyway, that the fewer windows you have to swap between, the faster you get to something satisfying and the faster you move onto the next task in your project.
Second, Serum does everything in stereo, which is not a luxury you’ll get if you only have one guitar pedal. There was a point where I was buying my modular effects and guitar pedals in pairs to have that stereo external effects loop and … boy that was not sustainable.
And finally, and most importantly, it makes the guitar pedal shareable. Like I put the whole chain into a Serum preset where you can load it up on your computer and get that awesome distorted sound without needing to buy or download anything else. I think that’s the most valuable part.
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If you have Serum 2, you can grab the above FX racks and all of the presets in our Maximum Overdrive pack. I think you’ll like it. It’s unlike any preset pack you’ve ever bought.
Thanks for reading, and take care!
- Geoff
