Embedded - 356: Deceive and Manipulate You

Episode Date: December 18, 2020

Leonardo Laguna Ruiz of Vult spoke with us about modelling electronics, modular synthesizers, and modulating sound. We talked in detail about applied digital signal processing. Leonardo’s website is www.vult-dsp.com. Check out the Freak Filter, the user manual alone is a course in signal processing. You can buy finished or DIY versions on vult-dsp.com/store.  The physical hardware is a Eurorack module (wiki) but the Vult modules are also available for the VCV Rack, a Eurorack simulator that you can use to build your own modular synthesizer.  Leonardo has a YouTube channel where he goes in depth on signal processing: youtube.com/c/LeonardoLagunaRuiz. He’s also written about modeling vintage analog sound on the Wolfram blog. For more information about the Vult programming language (or an example for how to build your own, check out the github repository: http://modlfo.github.io/vult/overview/ This episode was sponsored by Qt, a cross platform application framework for desktop, mobile and embedded devices. That means you get a full set of libraries for nearly everything you can think of, plus a world-class GUI that will give you a native look wherever your code runs. Try Qt for free at www.qt.io/download (qt.io/embeddedfm ! And check out Qt for MCUs!)

Welcome to Embedded. I am Alicia White, here with Christopher White. I think this week we should spend a bit of time talking about filtering, signal processing, music, and programming languages. Our guest is Leonardo Lacuna-Ruiz. Hi, Leonardo. Thanks for joining us. Hello, all embedded listeners. Could you tell us about yourself?

Yes. Leonardo, I'm a PhD in electrical engineering, and I kind of live a double life. During the day, I work as a software engineer in Wolfram Research. But during the night, I work as a software engineer in Wolfram Research. But during the night, I work on my own projects, which is, I have a small company called Vult, where I do mainly things related to sound synthesis. What does Vult mean?

Vult. I got the idea from some crazy dream where I had visions of vultures. And when I started developing these things and I needed to set a name, I said, ah, Vult sounds good

for vulture. Okay. It has been there for a while. Well, I think we're going to do lightning round now, and you're a listener, so you know how this goes. Yeah, and I'm nervous. Alright, ready?

Ready. Favorite chord? F-sharp. CV or MIDI? CV, definitely. What is CV? Control voltage, yes. Favorite instrument of all time?

I think it would be definitely the guitar. Especially the Les Paul model. I really like that model. Favorite fictional robot? This is a difficult question. I would say that my favorite is Ava from the movie Ex Machina, because it is like the only robot that, the only cute robot that shows the real intentions,

which is to deceive and manipulate humankind. Software or hardware? I cannot pick one. I think I will say both. Complete one project or start a dozen? I used to be the kind of person that started a dozen, but in recent years I have moved to starting only half a docent and finishing one. What is the worst 80s synth song?

I don't know. I mean, I was born in the 80s, and I'm pretty sure that there are lots of songs that are really bad that I never heard. So I only know the good ones. Very good, very good. Okay, let's get on to the longer questions, because some of these require a whiteboard, so we're going to have to talk around them. You said that the vultures told you to make filters. No, wait, that wasn't quite what you said, but something like that. Yeah, something like that.

What do you actually do in your spare time or in your non-work time? I like to do a lot of sound synthesis projects. And the filter part, it came a little bit late. So before I was just trying to program small microcontrollers to do wave generations, etc. But then one thing that I have seen while doing these projects is that the filters are almost never done digitally. Because from what I read, they always say, do your sound generators digital, but do your filters analog. And I was wondering why. So why the filters are done always analog

and then I fall into this rabbit hole of filters and I started making a lot of analog filters and modeling filters and that's how I ended up in recent years making mainly filters, digital filters

Christopher's brother Matthew plays guitar and has a large number of amps and says things like, these tubes are the best and I can only get them from Russia and they're marked radioactive or something. That's funny, you're just making stuff up. I am totally making stuff up. But he is very focused on the tube sound. Yes, and he likes analog stuff. Why do, I mean, does it really sound different?

Is this like having gold Ethernet cables? Not quite, but let him answer. I mean, probably, yeah, that is part of, is related to the gold internet cables. Because there is one thing that analog components have. They are imperfect, and they tend to sound more pleasant than the digital counterparts. So if I make a guitar amp that uses the lowest distortion, the best operational amplifier or integrated circuit,

and I plug my guitar, it's going to sound really nice, but it will not have that charm. So it's a bit like eating boiled potatoes and eating french fries the boiled potatoes are i mean they are good you can they're practically the same thing but for some reason the the French fries taste much better. And in the specific case of the two amplifiers, the fact that these amplifiers introduce a small imperfection to the sound makes the sound, specifically for the guitars, more interesting. So amplifiers amplify things based on the name, and filters filter things,

which seem kind of like the opposite things to do. Why do we talk about them together? So, I mean mean filters are they remove frequencies so we can think about them as amplifiers for frequency right yeah and in the case of

synthesizers filters are used in one specific kind of synthesis which is called subtractive synthesis in which you start with waveforms that have a high

that are rich and have a high content of harmonics but then you can put filters on them to remove some of those harmonics or to shape them just to get the kind of sound that you want. For example, I'm thinking in a very basic synth sound.

Let's say that I want to make a sound of a piano. It is basically, what I need is to model first the impact of the sound when i press the key and the and the string is hit that's like the attack right yes the attack and for that i i need more harmonics to to to have like this initial explosive sound. It's actually a high-frequency sound. I mean, it's got all of the frequencies. Yes. And as the string resonates, the higher-frequency harmonics are being consumed,

and then you get only the fundamental oscillation of your string, and that is very close to a sine wave so if i would if i would want to imitate that it will possible to use like first a hive as a an oscillator that produces more harmonics then i use a an envelope to to just like open the filter during a small period of time and then closing the filter gradually in order to get that sound, the release sound of the piano. So one of the things about synthesizers is it's not just

you have a filter and you set it to, okay, here's this notch I'm going to remove, or here's this set of low frequencies I'm going to remove. You actually manipulate the filter in real time as the sound evolves. So like change the envelope over time, so that if you press the same note five times, it sounds different? Even within the same note hit, it might open up or close. Yeah, that's exactly one big difference between the kind of filters that we study, for example, in electrical engineering. When you design a filter or when you read a text on designing a filter, you pick a frequency, you select your components, and you implement your filter.

But the musical filters need to be controllable. And they also need to be controllable in an exponential way. That way it matches the way the notes change. For example a C note in a piano you have many C notes in a piano and the difference

between those is that each each note is has the double of the it doubles the frequency right each octave it doubles the frequency and in in the case of the musical filters you want to control them in us in the same way so you don't say right now i i have Right now, I'm in 100 Hz, and then I'm in 110. The relation between the controlling voltage and the frequency is this exponential. So it sounds nicely in a musical scale. And you can go pretty far with that, too, to the point where you're only playing the filter. Like on one of my synths, I can set the filter to get into a kind of self-resonance. Yes.

And then control it with the keyboard. And so it's the only thing that's actually, it's getting some noise from inside whatever's left of the synthesizer. And that's resonating in the filter. But the filter's tuned with the keyboard so you're actually basically just playing the filter so in a in an electronic and electrical engineering term this is like terrible yes i mean this is this is the opposite of what you want but because you're doing music and music is often not intuitively mathematical, graspable. You go ahead and you use these effects. And that's also why people like tubes, is because they're imperfect.

Yes. I was thinking, for example, the other day I needed to rate a temperature using an analog voltage, and I wanted to convert it to use a simple amplifier just to get a wider range, I mean, a larger signal value. And the thing is that this sensor that sends, I don't remember exactly, but let's say that it sends me 10 millivolts per degree per Celsius degree I wanted to convert it to

2 volts so I need to amplify it a lot and so I make an analog amplifier for it the problem is that this analog amplifier can only output voltage that is between the... with a margin

like less than the positive power supply and higher than the negative power supply, right? So the two rails. It cannot... if I feed the amplifier with 12 volts, I cannot get 40 volts out of it not not for very long no yeah probably not for not for sure and the thing is is that that filter will be like very i mean that that amplifier will be very bad because i have very short range but if i plug my guitar on it and I use exactly that amplifier, I'm going to sound like Jimi Hendrix.

So from the engineering point of view, it's a bad design. But a musician definitely can do something interesting with it. Why? Why are our brains... Is it that our brains are wired to like the imperfections, or is it that we are culturally wired to prefer these things? I don't know the answer.

Yeah, there is one thing that the distortion makes, and it's easy to measure. When there is a little bit of distortion, we're introducing high-frequency harmonics. For example, if we have a pure sine wave and we see the spectrum, you will only see one bar, right? One point.

But when you add a little bit of distortion into this waveform, you will see that in your frequency analyzer, they appear like small frequencies, higher frequencies. And the more you distort it, you get more of this, and it just makes it sound more appealing. So if you're going to make a model of an analog synth or an analog circuit as part of a synthesizer,

you're actually going to do this in digital, how do you, do you just play one of the original and capture it spectrum, an an envelope and then recreate it? Is this how you go about modeling it? Or is there a different way? No, a little bit different because if I... Okay, I'm going to

tell you a little bit about the process. So, what I usually do is I take one of the existing filters. There are lots of schematics online that you can find. And let's say that I pick one of those. And then I start analyzing what's the basic architecture of the filter.

So if we take one, let's say a salen key filter which is also quite common salen key ok that's it's a high pass low pass filter yes and many of these musical filters

have a variation of this one but in order to change the cutoff frequency in this architecture

in the salen key you need to change the resistors and many of the synthesizers

since you don't want to put variable resistors there you want to control them with voltage there are

different ways of doing that for example example, with diodes and changing the biasing of the diodes, you can put transistors, FETs, etc. in order to simulate to have this variable resistor. So what I started doing is using this program that I write,

this simulator that I write in Wolfram, I started making a component model of this circuit. So, I mean, you can think about it as just making a SPICE simulation where you put all the components, right? Okay. The main problem with the SPICE simulator is that the models maybe are too complex. If I put like an operational amplifier model,

it will contain minimum 12 transistors. I'm simulating like these 12 transistors. But with the simulator that I use, I can replace that complex model by a simpler one. For example, in the case of the operational amplifier, the simplest model will be just measuring the voltage between the inputs and adding a gain. And then I can consider other effects. And this is where it starts getting interesting. So let's say that I make my model, I use resistors, capacitors, and an operational amplifier. If I make this model of the operational amplifier linear,

I will get a linear filter. And the linear filters sound okay. But if I want to simulate the analog feeling of this, what I need to do is to make a model of the operational amplifier that behaves just like my real amplifier, which will be, it has clipping. It is exactly what I mentioned before. The amplifier cannot output more voltage than its rails.

Then I have to add like this limiter. And once I put this nonlinear operational amplifier, my filter is going to be nonlinear. And from this circuit, just by following the basic electric analysis methodology, like getting all the currents of the nodes, that I can start simplifying more and more until I get the smallest representation that will be a set of nonlinear differential equations. And this will be the smallest representation of my model. And these are the equations that I need to simulate in order to imitate this specific filter. So it's really a component-level model that you start with,

not a behavioral. Well, it depends. It's a mix. It's a mix of it, yes. But I usually start with the component level because at the component level is the one that allows me to analyze which things are the ones that I have to model. So let's say that my filter has four operational amplifiers. Maybe not

all the four need to be nonlinear. And in order to determine that, I usually just do a comparison with the real circuit, which I either made it in a PCB or have it in a breadboard. And then I input a signal and I check, okay, so if I put my filter into this configuration, what's happening? Okay, this operational amplifier is saturating. This one, it always works in the linear region. Then I can replace it for a smaller,

for a simpler model. And yeah, that's part of the analysis. Trying to figure out what are the things that matter and what doesn't matter in order to get a simpler model. Are there any popular filters that have just not fallen to this technique that are just too complicated? I'm not sure.

I think that at least I have been able of simulating reasonably well most of them. But the problems that I have had is that since I want to model this filter and then simulate it in a microcontroller, I don't have enough CPU to do that. And then I have to drop details of my models in order to be able to simulate it. So my model will not sound exactly the same, but it will sound pretty close. And it will be much more efficient. To give you a specific example, I was modeling a filter found in a Russian russian synthesizer called the the poly box and they use

this special operational amplifiers that in which you can send a voltage and that controls the bandwidth of the of the amplifier and in order to model that, so first I had to get the operational amplifiers, then making the model. And the model that I got, it was too complicated. I mean, the differential equations were very hard to solve. And then I had to simplify a bit my model in order to get something that sounds close,

but it doesn't sound exactly as original. Have you trained yourself to hear the differences, and does that affect your enjoyment of music? Yeah. The worst thing about working with something like this is that you cannot listen to music while working because I need to be listening to a continuous waves sound for a long time, for a long period. And also the ears get tired. So I also use a lot of frequency spectrum just to find out to help me

visualize what I'm hearing. Yeah, that's bad. And also my wife gets very upset because I'm playing a sound two hours. We're sponsored this week by qt or cute i'm super excited to have cute as a sponsor as i've been a fan for years i built entire medical devices using cute as well as tons of small utilities for things like firmware update and microcontroller config cute is a cross-platform application framework

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and sign up for a free trial. It includes all the frameworks and development tools along with a bunch of cool demos of desktop, mobile, and MCU applications. Qt made my development life so much easier dozens of times, and I think it can do the same for you. Thanks again to Qt for sponsoring this week's show. I wanted to ask, just briefly before we move on,

about the, you said you get it down to a minimal set of nonlinear differential equations, and those are not easy. There's various techniques for solving nonlinear differential equations. And those are not easy. There's various techniques for solving nonlinear differential equations, but they aren't as approachable as linear differential equations. What methods do you use to solve them, and how do you fit that into a micro? Yes, so I use, depending on the filter, I have, I mean, one of the advantages that I think I have is that in my real work, I develop a simulator. And over the years, I have accumulated a lot of knowledge on how to simulate differential equations. And in order to fit them in the microcontroller I use a lot of things, for example, one of the

part of my analysis, once I have the differential equations, is to find a method that is suitable for this set because if I want to simulate an RC filter made with one resistor and one capacitor, probably the Euler differential equation, the Euler method for solving differential equations will be enough. So I don't need to have to do more. And if not, for other filters,

what I do is try all methods that I know, from Hewn method, from Kekuta trapezoidal integration and then I try to find which one fits better into this to solve the equations and to have more or less accurate results and then there comes another problem which is performing the computations

and since I have non-linear elements and I have to do iterations Then there comes another problem, which is performing the computations. And since I have nonlinear elements and I have to do iterations, I have a bag of trickery to write the code. For example, using a lot of lookup tables in my code to try to speed up the computations. If I have like a long formula that I need to evaluate and it's only one variable

it works making a lookup table for it so yeah from all the equations I try to do that and also I try to use mathematical simplification as much as possible in order to reduce the number of multiplications, which are usually the ones that tend to be more expensive.

It sounds like it's mostly time domain, though. When I was doing this stuff years ago, one of the techniques was to do a Fourier transform of the nonlinear DE and then do like Rangakata in frequency space and then move back or something like that. But this sounds like all time domain. Yeah, I usually do the time domain because once I have this set,

I mean, if I apply this technique and I make it efficient enough, it will work fine without doing back and forth Fourier analysis. That's cool. Well, one of the problems with doing the Fourier analysis is you need a window to act upon. And as soon as you have a window to act upon, now you're delaying your signal.

Yes. And that has all kinds of problems associated with music. Yes, so one of the big problems in the filters is that you usually have feedback paths in the circuit. So if I

split let's think about one of the popular filters the Moog Ladder filter which is basically four low-pass stages let's think about one of the popular filters, the MOOC ladder filter, which is basically four low-pass stages, and then you have feedback. If you model this one as four separate low-pass stages, and then you take the output sample

and you feed it back to the input, you get a filter that sounds different because you have a delay in the output and and in order to avoid that i i need to analyze the system including the feedbacks and that's usually why i need to solve the differential equations because i i need to iterate I need to have the iterative method in order to solve this feedback path. You've implemented a pretty long list of filters, but I don't know what they sound like. Are there ones that I would recognize based on certain songs, or are there ones that are special beyond those we've talked about? I don't know if you, I mean, not you, but a person that is not into the synthesizers will recognize them. I can't even tell. I've got several, and I kind of know what these things do. I couldn't tell you which filter was which in a song.

Okay, then tell me about this one. Debridatus, a wave destructor with bit crusher, wave fold and distortion? Yes. Yeah, that's not a filter, definitely. What is it? That's another. So in this module for your hack that I make, I included a lot of filters. So most of my filter models are implemented into this module.

And it's possible to switch between them just by the press of a button. And since I have a module that can do that and I have a processor so I decided to put some of my other virtual modules into this one into this real module and that is basically a distortion

because you can always take your audio signal spice it up a bit with a bit crushing saturation distortion, and then put a filter after it to get it back to nice levels. A bit crusher is that's where you take the bit depth of a digital signal and chop it off, right? So if you have a 16-bit digital signal, you truncate it to 8, and it sounds grungy and gross, and then you fix it up with a filter.

You mentioned Eurorack and modular synthesizers. Could you explain what that is for people who aren't surrounded by a lot of synthesizers? I have no Eurorack in this house. Is that what you want for Christmas? Sorry, go ahead. Okay, so basically the common synthesizers that people may have seen, they consist of a bunch of buttons in a keyboard

form factor. Yes, yes, I see that. And those are the fixed synthesizers, let's call them that. So integrated synthesizers in which the architecture of your sound, I mean, of your synthesizer is a little bit fixed. It follows a traditional path in which you have sound sources filters and then

you have modifiers and you can do a lot a lot with those synthesizers but there is this other kind of synthesizers which which are the modular and one of the most common form factors is this one the euro rack and the main difference is that instead of when you buy when you want to build a synthesizer instead of buying one that has everything you buy individual modules so you can say i want an oscillator and i like this one from this manufacturer because it makes this and that so you you buy that one, and you have an oscillator. And your panel, the panel of your module has jacks, audio jacks, and then you can just take that audio signal

and insert it into any other module that you want. So you can say, I want a filter, and you buy like a one, two, or like me, you end up having 32 filters, 32 analog filters. So you pick one of those, and then you can send your signals. So the main difference is that you have full freedom to construct your synthesis machine and to rewire it with physical cables.

Like, if you were to play this live, would you be rewiring it live? Or is it you wire it and then that's how it sounds for however long this song takes? It depends on the artist. I have seen a lot of videos of people that actually play live

with modular synthesizers and they usually have it a little bit fixed because when you have a synthesizer that is that big with so many cables, it may be hard to rewire live, but you can always do a little bit of patching so probably changing a few of the jacks that you remember.

I have a small Eurohack synthesizer and I have probably 60 patch cables and when I'm designing some sound sometimes I use them all and I'm not doing anything complicated like a live performance so I cannot imagine a live musician

patching 60 cables in a single session most of the time they're probably twiddling the knobs and things that affect individual modules and not rerouting things. Yes. And there are even modules that help you do that. If you don't want to change cables live, you can add a module with switches. Then you can just toggle switches to change your routes usually what happens to me even when I'm using a non-modular synthesizer

is I'll start playing with it and then not make any music because I'll be so busy changing routing and getting so into that part of it like oh I'm designing this sound, oh what if I connect this to oh what if I turn this knob three hours have gone by and I haven't actually

I mean it's fun yes I's i agree that that's what i usually do i i never so i i just get lost in into the sound design so bad that i haven't made any song in four years or something three or four years or something, three or four years. Just sounds. But you have been making this unit that can go into the Euro rack that then can model, simulate, mimic a whole bunch of other different modules that would normally go in the Euro rack. Yes. Yes.

So that's, I mean we before we have been talking a lot about the filters and i do all this i mean i do all these models because i want to put them into this module which has another microcontroller and the idea behind that it was to have this digital module that, just like the robots that I mentioned before, it tries to deceive you and manipulate you to think that it is an analog filter, but it is not. It's digital, but has the advantages that you don't have

to use a lot of space with a lot of filters, and maybe if you're just picky like me, you want a specific sound, and then you can easily just change which filter you want for this specific sound. Well, then you don't need to change the patch cables. You can just change which filter you want. Yeah, I mean, you can change the filter, but you can still change a lot of things

in your sound generator. There's a completely simulated Eurorack called VCVrack? Is that right? Yes. So VCVrack is

this open source Eurorack simulator, which was developed by a person called Andrew Veldt. And since it is open-source, it is very easy to create your own modules. And it simulates the Eurorack because it follows the same form factor. You have also traditional Eurorack because it follows the same form factor. You have also traditional Eurorack panels. And then you can do all the patching with wires. And it tries to simulate all except the bad things.

For example, you cannot connect outputs to outputs. Or it doesn't let you input to inputs. And yeah, it is really nice. So I actually started developing all this for VCVHack. Since I've been developing modules for a long time, when I found that VCVHack was going to be launched. I did... My first module was this virtual filter for VCVRAC. And I got excited and I kept doing more and more and more.

And what I did was, once I had all these models, up to that point, I started thinking, maybe I should make a Neurorack model with this. And then I ported back everything to hardware. And what I'm doing now is backporting again. So I want to do like a clone of my own Neurorack module, but for PCBB rack. So that will simulate all the parts, like even the LCD screens and stuff like that.

So yeah, it is very approachable, VCB rack, because Eurohack is expensive. I think it's funny that you started modeling hardware with software. in this sense because I have software that simulates analog and hardware that simulates digital. Shifting gears a little bit, you have also made a language to help you with the signal processing pieces. Could you tell me about that? Yes, I have the Vult language, which is a very simple language that I developed

to gain kind of portability because some years ago when I was doing all these synthesizers using different microcontrollers, I would make some piece of code, for example

for a DSP. And when I have had something done, then a new development board comes out and I want it and then I develop something for it. And I started getting problems like moving my code. So I decided to make this layer on top of C++ that will be a much simpler language, less things to worry about, and that I could later create different generators to target the different platforms that I wanted to do.

So, for example, I will make with this full language an oscillator, and then I could, if I wanted to run it on a web browser, I can generate JavaScript and then use the Web Audio API to test the sound, or even develop it directly in the web browser. Once I'm satisfied with it, I can generate the C++ code that I want to run, for example, on a TNC board or probably in an Arduino if it's possible,

without making changes. So I wanted to concentrate all my development into this language and being able to move it, but also adding features that I always use. For example, creation of lookup tables. And in other projects where I have done with lookup tables, I use like any external software to do the calculations and then write a file and then doing it into C++.

But with the Vult language, I can just write a formula and say, like, this formula is going to be a lookup table of this size. I'm going to use interpolation, et cetera. And when compiling the code it does all the calculations and I get the optimized code. And I also have features or more restrictions in the language. For example, when converting integers and floating point values.

One error that I hit a lot before, it was in C++, when you write a number one, it can be an integer, it can be a double, it can be a floating point, I mean, double precision or single precision. And if you write the incorrect one,

the C compiler will assume which one it is right. So it can be that you wanted to use single precision, but since you didn't write the F after the number, it thinks it's double precision, and then your compiled code could be making double precision calculations and then convert it back to single precision. And I found that that was actually consuming time. So in the language, I also put very strict restrictions

on conversion of types. Everything needs to be explicit. And yeah, a lot of small things like that I cover with the Bool compiler. And that's what I use for my development. Are other people using the language or is it just for you? I mean, I'm developing just for me. And there are a few persons that use it and a lot more trying to use it.

But since I don't have very good documentation on it, maybe that's a key factor. But at least the persons that I know that use it, they like it a lot. And do you, would I have to already have solved all of my equations and this is just putting in the forward methodology or will it also help me figure out the equations, the differential equation solutions? No, for the differential equations, the full language is just for the final implementation.

Okay. And for doing all the differential equations, as I mentioned before, I work in World Frame Research, and I work in the group that develops Wolfram System Model, which is a tool for modeling systems. And that's the software I use where I do all my work with the electrical components. And it's a graphical interface, right? So I can recreate my whole circuit with that tool. And then I use Mathematica to extract the equations.

And in Mathematica is where I do all the manipulation and all the testing and prototyping at the equation level because it has a lot of tools for doing that. That's mostly symbolic manipulation at that point, or is it already numeric? No, no, it's completely symbolic. Okay. Because I want to get, I mean,

I want to really use the symbolic capabilities to eliminate as much as possible of the calculations. You say you don't have good documentation, but I'm looking at the EZDSP with Volt page, and it walks through the whole thing. It starts with a filter and shows how to write a function that matches that filter,

and then... So, yeah, I mean, obviously it's not going to do the hard part for you of doing the math, but this starts with that a little bit and goes through it. Yes, yes. Yeah, I mean,

I don't have documentation for all the cool features for the new features that I have implemented. Does it integrate with the VCV modular synthesizer? VCV rack? It

integrates through a plugin. In VCV rack, there is a plugin that is called the VCV Prototype. And that module allows you to write in a single file code and then test it. And I use that one a lot as well for my development. So I actually contributed that part of the plugin, being able of running Vult code in real time. So when I'm developing, I open this module,

and then I have my text file with my code, and I type it, and when you save, you hit save, it immediately starts running in VCV rack. And it is really, really useful that you can just test, prototype and test the code. Really cool. Look, I don't need any more hobbies, Leonardo. This is very awesome

stuff. I will send you some links later. If someone hypothetically wanted to get started with this, with creating the models and maybe not having a PhD in this sort of thing. Is there a way to get started? Yes.

I think that, I mean, the best, it totally depends on what you want to achieve. Because you can do modules that are nice, that sound nice, that are useful, and that do not require all the kind of detail that I put behind. I just do it because I know how to do it. And definitely the best way to start

is for example with VCVRAC and I actually have some tutorials I recorded like a three hour tutorial on YouTube, on my YouTube channel where I show the whole process that I follow

and even so I show the modeling part and also the implementation. That will be one of the resources that you can use. But definitely a person does not need to go into the modeling in order to do something

interesting. And that sounds nice. If you want to go into the modeling, probably it will work revisiting all the theory behind electric circuits and simulation methods, etc. I have a listener question from Emily. As someone who's always interested in modular synths, but put off by the price, do you have any advice for how to get started on a budget? Is this going to

be VCV rack? Yes, I think that the best way of doing that will be using a hybrid set setup. So you can install VCV rack for free, and then you can get a module that converts, that helps you bridge the modular side and also the real Eurohack and the virtual Eurohack. And there are different modules. For example, the Expert Sleepers modules, which they are basically a sound card with many channels. And that helps you combine

virtual modules with your real modules. So if you have like on the virtual side you can have a thousand modules, then you have your bridge and a few Eurohack modules just for the

sound design or also, I mean, the real UroHack has the advantage that you can touch the controls. And that helps you a lot when performing and when doing,

when experimenting. So the models that you think that are good for UroHack, to have on the UroHack side, so the models that you think that are good for Eurohack to have on the Eurohack site you can pick those and use them there so definitely

just going back because a hybrid setup of something virtual and analog sorry, something virtual something real in the bridge, it will be a good start point. Are the VCV rack modules expensive? No, no, no. The software is open source.

There are like almost 2,000 free modules. I have myself, I have probably 20-something modules free. And there are a few that are paid modules. And those tend to be cheap, probably less than $20. So if I wanted to try modular synths for really cheap, I could do all virtual and then slowly build up into physical world as well. Yes.

And that will help you a lot to decide what you want in the real world. I have one more question that I think is just going to be the end of the show. And that is, I hear you're coming out with something to do with drums. I didn't tell Christopher that ahead of time oh yeah so the last months i've been modeling drums analog drums and they just go bap bap bap right why are you like this something like that boom and this this drum modules are kind of fascinating that how how the the original designer of the circuits develop them so if if one thinks how how can i make some like a cymbal sound? Oh, yeah, I just need a noise source, envelopes, etc. Or a clap sound.

That was super interesting for me. Because how one would make a clap sound? And while I was analyzing those modules, I found out a lot of interesting things that if you don't model something, if you don't model the behavior or the transition curve of this transistor, you don't get a good sound. So, yes, I'm developing drum models,

and probably in the future I will make another hardware module containing those. Wait a minute, go back. If you don't model the what part of the drum sound? The transition, I mean the non-linearity of the transistor. Oh, okay. Yeah, because drum sounds are weird. It's super impulsive. Synth sounds, you can get your head around it.

Okay, I've got a sine wave or a triangle wave and then I do this and that. But drums are a very complex mix of noise and transients and also pure tones and resonances. Like for a bass drum, bass drum is a very low pure tone combined

with the slap and all that stuff. I've always been kind of fascinated by the analog drum synthesizers because it's like, okay, they always been kind of fascinated by the analog drum synthesizers because it's like, okay, they have to kind of purpose build a bunch of circuits. It's not just one synthesizer that you can kind of make anything with. It's like, oh, I have to have something over here to work to make a snare, but it doesn't really work for the kick drum, so I have to have some extra stuff for that.

Is that right? They kind of have to be a little bit purpose built? Yes. For example, the case that i mentioned before with the clap you have you have a like some noise source and then you have envelopes to to do the triggers but in order to uh when i was trying to model it there is a part in which you see a VCA it's basically a multiplication and if you do a basic multiplication of the voltages you don't get the sound so it needs to be like this specific

transistor based VCA that way you get the correct transient when modulating the amplitude. And only if you use this VCA, you will get something that sounds like the original. Wouldn't it be simpler to model the original sound? I mean, model the hand clap instead of model the transistor electronics that models the hand clap?

How do you model a hand clap? I mean, you can always record the hand, like people clapping and use a sample. That's the simplest model, probably. I mean, there are physical model physical modeling synthesis like where you just either piano models I have one that's quite good and it's totally fake and they've gone through and figured out how pianos work and model it that way but I know that's more of a simple thing with you have a hammer and then the pure tone from the. I don't know how you'd metal something as weird as just an impact with skin.

That's interesting. So one, one, one interesting thing about the, the, like the drums is that the, when in the, for example,

the 808, the Roland 808 drum machine, the designers were trying to, to do something that sounded like drums. It ended up not sounding like a real drum kit. But the fact that that sound was different and unique, it made it super influential in the 80s music. That's probably like the most famous.

When people think of analog drums, that's the synthesizer I think people gravitate to thinking about. Yes. I'm still boggled by you going through electronics because it seems like the physical model would be simpler. And the electronics people had to have done the physical model at some point. Well, but correct me if I'm wrong, you're following on from the analog drum sense of the past, so you're trying to recreate that sound. You're not out there to make realistic drum sounds in an analog synthesizer. What I'm actually interested in is learning how these

drums work. In my learning process, I end up recreating them and then I can just publish them for other people to use. Yeah, if you want to make realistic drum sounds, you sample them. Yes. I have a question from Tom. Are the virtual synths really a good try-before-you-buy sort of representation, or are there important differences between hardware and software implementations? Okay, so actually in this question I didn't understand very well if it's like in general or for my specific…

I think in general or for my specific? I think in general. Yeah, in general. I mean, I'm hoping that for your specific, you'll say, oh, no, they're rock solid right on. But in general, are there things people should look for that indicate the differences are likely, or is this just a matter of reading the reviews? I actually don't know how to answer this one because as we were talking before, almost it's like everything works. As long as you like the sound, everything works.

Yeah, that's the thing about synths is you can get into a battle about virtual versus real and it's like, if it sounds good, who cares? Yeah, I think that the main difference will be just the interface the fact that you can touch it is is what makes it different that's a pretty big deal and i mean if if we reroute the question to my own stuff in my personal case the stuff that I have for free

for free it wasn't intended as try before you buy but what ended up happening is that a lot of the people that tries my stuff they tell me yeah I really like the filters. That's what I decided to get the hardware.

Cool. And we've talked a lot about all of this, and you've mentioned your job, and you've mentioned using the simulators that are part of your job to fuel your side gig, fuel Volt. How do you lead this double life? How do you have time to lead this double life? It's complicated so in Vult I usually work just one hour two hours

during the night and during the weekends but one nice thing is that since I'm using the tool that I'm developing for Wolfram I usually come up with things that

okay, maybe, or it will be something like, probably I found a bug because I'm using our own tools or I found something that needs to that could be improved and at the same time I have published through Wolfram

some of the work that I do with Vult. I publish a blog post about how I use the tools to do that. So I think that we have a kind of symbiotic, a nice symbiotic relation in which this, that is my hobby, helps me with the work that I do at Worldfront. Also, in the development of the compiler, there are things that I try in my boot language,

experiments that I do, and sometimes I say, oh, I really like the way that I made this part of the code. Probably we could apply it to the product to do better code or something like that. Leonardo, do you have any thoughts

you'd like to leave us with? Yes. I was remembering the phrase from a famous statistician that said that all models are fake, but some models are useful. And that's kind of the mantra of my life.

Our guest has been Leonardo Lacuna Ruiz, founder of Vault. Check out his site, vault-dsp.com. We have links to that in the show notes, as well as to his wonderful YouTube tutorials. Thanks, Leonardo. Thank you. It was my pleasure. Thank you to Christopher for producing and co-hosting. Thank you to Leonardo again for suggesting he be on the show and in the subject saying he wasn't a robot. And of course, thank you for listening. You can always contact us at show at embedded.fm or at the contact link on Embedded FM. And now I have a quote

to leave you with from E.O. Wilson, which I always think of him as the ant guy because that was the first nonfiction book I read that I enjoyed. We are drowning in information while starving for wisdom. The world henceforth will be run by synthesizers. People able to put together the right information at the right time, think critically about it, and make important choices wisely.