Introduction to Audulus and the Expert Sleepers ES-8 DC Coupled Audio/CV Interface

Expert Sleepers ES-8 and Audulus: The Perfect Pair


Audulus is a modular synthesizer programming environment for iOS, Mac, Windows, and Linux, and it can be used in conjunction with the Expert Sleepers ES-8 DC-coupled audio interface to augment your Eurorack modular synthesizer.

Advantages of Audulus + ES-8 Hybrid System

  1. Economy - An Expert Sleepers ES-8 is $475. It’s an expensive module, but it is well worth the price. Why? Because once you have one and use Audulus with it, you can use your ES-8 to replicate the functionality of tens of thousands of dollars of modular synthesizer gear.
  2. Versatility - The ES-8 is like a blank slate - you can make it do whatever you “program” it to do with Audulus. You can think of it like a super Disting multifunction module. There are already many clones of Eurorack modules in Audulus that, when paired with an ES-8, are essentially functionally identical.
  3. Recallability - Analog is great for a lot of things - one this it isn’t great for is recallability - especially when it comes to sequencers. One thing that’s not so great about modular is switching quickly between two patches. Audulus and the ES-8 allows you to do this quickly and easily by merely opening another Audulus file. The way I have my modular set up, I can go through a whole set of songs, each with different drums, different routing, different oscillators and sequencers and quantizers, all instantaneously. Each song will play the exact same way every time (that is, if I want it to).
  4. DIY Originality - Don’t know how to DIY your own Eurorack modules with electronics? Don’t understand how to hack your digital modules with your own code? You can do the next best (and much easier) thing and create your module in Audulus. The added bonus is that if you use your iOS device, you can have a touch screen interface for your module as well! And if you have an idea that you don’t know how to translate into Audulus, we will help you.

DC Coupled Audio Interfaces

A DC coupled audio interface allows you to pass not only audio, but static offset control voltages, like gates and 1 volt per octave pitch information.

Most audio interfaces are AC coupled, meaning they filter out DC offsets. If you tried to send 1vpo signals through an AC coupled interface, it would never stay in tune.

Expert Sleepers ES-8


The Expert Sleepers ES-8 Eurorack module is a 4 input 8 output high resolution audio DC-coupled audio interface (expandable to 12 inputs and 16 outputs). Each input and output glows red for positive voltages, blue for negative, and a steady purple for audio - which, by the way, matches the Audulus red/blue aesthetic nicely.

ES-8 vs. Alternatives

While we highly recommend you use an Expert Sleepers ES-8 as your Audulus-to-modular interface, you can of course use any DC coupled audio interface, which include all of the Universal Audio interfaces.

The reason we recommend the ES-8, however, is that not many (or any I know of as of this writing) interfaces can do everything that the ES-8 can.

  1. iOS connectivity - immediately and seamlessly pairs with your iPhone or iPad without the need of drivers.
  2. Voltage Range - The ES-8 has a voltage swing of -10 to +10 volts. Not only is this a nice round number, it also interfaces very easily with the -1 to +1 output range of Audulus. This means every 0.1 interval in a signal in Audulus is equal to 1 volt. Most other interfaces only go up to 8 volts, which means each volt is equal to intervals of 0.125 in Audulus, and you are limited to 8 octaves of vpo tracking (which can be troublesome especially when doing FM synthesis).
  3. Convenience - The ES-8 screws directly into your rack - no muss, no fuss, no “dongle” interface with a separate power supply.

Building a Eurorack system around the ES-8 and Audulus

If you’re new to Eurorack and like the idea of a hybrid Audulus+ES-8 system, follow the steps below. If you’re a seasoned modular synthesist, skip down to the next section.

  1. Buy a Eurorack powered case. There are many options to choose from. I chose a small mobile rig made by Pulp Logic that fits in my backpack. I like the idea of being able to bike to a show, or to a mountain getwaway with my Eurorack system. Perhaps you’d like a larger case that has room for expansion. While many may discourage you from getting a small case to start with (such as the Doepfer Mini Case), small cases will always come in handy later, even if you move on to a larger system, because you can always use them as a “overflow” for new modules.
  2. Buy an Expert Sleepers ES-8. Choose from the long list of Expert Sleepers vendors and buy an ES-8.
  3. Decide what your first module will be, and buy it. What you buy first depends on how you want to balance the relationship between Audulus and your Eurorack. The safest bet for a first module, though, is a filter. I would suggest starting with a Doepfer filter. Doepfer has a large line of these, and each one has its own unique sound. With just a filter and an ES-8, you can create a synthesizer in Audulus that has digital oscillators, envelopes, and VCAs, but using that external analog filter can add a lot of magic to your sound. Another great first module would be a distortion, which, like analog filters, can be difficult or at least resource-intensive to model in digital form. By “offloading” the job of filtering to an analog filter, or distortion to a module like the Erica Synths Fusion Tube Mixer, you are reserving CPU time (read: computer power) for more tasks that don’t require an analog circuit to “sound” analog.
  4. Use Audulus to explore modular synthesis as a concept, and expand from there. You may like the idea of using a real CV sequencer with Audulus - say a big fancy one like the Klee. There is something to twisting knobs that’s really enjoyable and changes the way you interact with something. I personally enjoy the instant recall of having Audulus take care of all my sequencers, and I use my Eurorack mostly for its filters and distortion/overdrive. But maybe you like the Make Noise Pressure Points controller, or perhaps an analog delay effect from Pittsburgh Modular, and want to use those with Audulus. There’s no wrong way to do it, but it does behoove you to have patience and really think and plan what you want. ModularGrid is an excellent tool for planning your rack going forward.

Audulus and the ES-8 for the seasoned Eurorack synthesist

As someone who is established in Eurorack - in its language and its workflows, you may be wondering what Audulus can add to your modular experience. Here is a short list in no particular order of uses of Audulus you may find exciting.

  1. Audulus iOS+ES-8 is a touch controller. You can use it for its buttons, its on-screen keyboard. You can add extra digital knobs or triggers to modules you already have. We’re also discussing a new feature for Audulus 4 that would allow you to create your own custom XY pad controllers - XYZ controllers for devices with 3d touch. Below if a video of a “quantized” XY controller with an 8x8 grid of connection points.
  1. Audulus+ES-8 is a blank DIY Eurorack module. If you’re not a screens person, you can still use Audulus and the ES-8 together to create your own custom module. You can just pretend the ES-8 is a module without any knobs (or use external DC offset knobs at inputs 1-4 as knobs). With a creative combination of knobs and buttons (found frequently in 1U racks) you can basically make a Frankenstein module that uses real analog controls to control a digital program that creates real analog CVs (just like many of the, say, Mutable Instruments modules do - though they are written in text code rather than visual programming). You could make it a sequencer, a filter, a reverb, a chopped & screwed delay, an modulated clock divider - anything you can imagine. Pictured below is a [ready-to-go “blank” ES-8 module](ES-8 Audulus Module Template.audulus (78.5 KB)
    ) waiting for you to fill it with your “circuitry.”


  1. Audulus+ES-8 is a way to “demo” cloned Eurorack modules. There are many patches available for Audulus that identically (or nearly-so) replicate real Eurorack modules. If you’re wondering how that module might fit in your system, Audulus is a great way to “demo” a facsimile of the module to see if it’s something you’d like to buy. How much this works as a 1:1 analogy will depend on the model being cloned, but it’s an option. This is where all of the Eurorack clones are kept on the Audulus forum. Examining the clones, or creating one yourself, can also be a wonderful exercise in understanding the design on a much deeper level than you might if you had merely read the manual. Pictured below are a few versions of a Turing Machine that Audulus user stschoen has made.

  1. Audulus+ES-8 is an ultimate utility and digital VCA module. As we all know, you can never have enough VCAs. Well, with Audulus, you can never run out of VCAs. There is no explicit “VCA” module in Audulus, but you can use a Multiply node as if it were one. You can also attenuvert, active buffer, mix, modulate, amplify, compress, sidechain, cross-modulate, feedback, sequential switch, logic gate, and more. One output could be a vpo signal, another an LFO, another a sample & hold based off pink noise, another divided clock signal, convert Euro vpo to Buchla standard, Buchla to Korg, etc., etc., etc.

Digital hybrid vs. all-analog system

You may expect me to say no, but the truth is, some people’s approach modular synthesis is a philosophical rather than merely pragmatic one. I was originally attracted to modular synthesis as a way to create a kind of DIY synthesizer but selecting particular modules and putting them together to create my own custom sound. Others however feel inspired by a modular-only workflow that doesn’t involve any screens.

If you feel like hardware-only is something that excites you, then by all means - more power to you. In this world of virtually infinite choices, some self-imposed restrictions can be healthy and focus your energy to unexpected and wonderful results.

I prefer a mix of limitation and limitlessness. In one sense, I’m “stuck” with the sounds that my hardware modules make, but I can use Audulus to make them sound however I want.

How to move forward from here

This thread is a perfect place to ask questions and engage with us and other Audulus users on how to create your own hybrid digital-analog Eurorack system.

If you have a dream module you’d like to create using Audulus, describe it below, and we’ll help you make it a reality in Audulus.

If you are interested in learning how to use the Expert Sleepers ES-8 as a blank DIY module, refer to this post on the Audulus forum and the videos below.

In a future post, I’ll go in depth about my personal modular synth (pictured below) - how I picked the modules I have and the thinking behind its semi-permanent patching.

Audulus + Expert Sleepers ES-8 Videos


The ES-8 is a fantastic bridge between the world of Eurorack and Audulus. Endless fun.

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Noticed that the link to the Eurorack clones is not working. JSYK.


Thanks that’s a reference to the old forum I’ll fix it!

A lot of great info here. I love my ES-8. Anxious to try this out. Thanks!


It’s the good stuff!

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I actually haven’t used my ES-8 with anything but Audulus!


Finally got my ES-8, that I ordered over a month ago.
I have it communicating fine with VCV Rack on Windows PC, but for the life of me I can’t seem to figure out why/how to get it working with Audulus.

If I click the ‘test’ at the audio settings device selection all the ES-8 outputs do light up.

I’ve watched the vids but I remain clueless.

I’m only 50% clueless now. Got signal from Audulus out through the ES-8 but still at a loss for going the other way.

Maybe someone can point me to the correct Input Node.


The windows version of Audulus is in need of an update. Currently the mic input node and speaker node are 2 channels of I/o that you get to work with. Hopefully @taylor will surprise us with an update really soon.

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doesn’t seem to be available. But can the disting mk4 be used as a pared-down version. r 2emulation?

Two things: Audulus doesn’t work with aggregate devices at the moment, so the only way you can really get it to work is to use the standalone version of Audulus and set your system audio to the ES-8, then use a DAW to record/monitor it by setting the ES-8 as the input and your speakers as your output in the DAW.

Does that make sense?

Does this mean that I can’t use something like Beatmaker 3 as my iPad DAW and then run Audulus as inter app audio to control a modular?

Can you explain this setup a little more? Also, aggregate devices aren’t something you can do on iOS anyway. If you plug your iPad into an ES-8, you have to take the audio output from the ES-8 and feed it into a headphone mixer or something to monitor it.

Does this mean that I can’t use something like Beatmaker 3 as my iPad DAW and then run Audulus as inter app audio to control a modular?

Can you explain this setup a little more?

Can I run Audulus as a plugin on iOS and have it interact with a modular? I don’t know how to put it another way. I know you don’t have AUv3 fully happening yet (but we do have Inter-App Audio) and there is no midi out, but maybe you could just say what the ES-8 is doing with Audulus. I take it that it is providing a DC coupled interface and somehow passing some control voltages back and fourth. But when you started to talk standalone only, my mobile production studio dreams felt threatened.

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When an app is using IAA or acting as an AUv3 plug-in, the I/O comes from the host application rather than a physical I/O device. Currently, when Audulus is running as an IAA or Audiobus app, it is limited to 2 channels of audio I/O which are connected to the IAA or Audiobus host as a stereo pair (channel 1 and 2). Physical inputs and outputs are linked to the IAA host (e.g. AUM or Beatmaker). I have tested using a Focusrite 6 channel I/O unit with AUM and I can route any two input channels from the 6i6 through AUM to Audulus as an effect or output two channels from Audulus via AUM to any two 6i6 output channels , and route the other channels to other apps or plug-ins. Of course, when using IAA you can only have one instance of Audulus running. While there are some apps that support multiple audio channels via IAA many do not. I personally have a few (Loopy HD, Studiomux, Thumb Jam, AUM, etc.). Both Beatmaker and AUM support them as hosts. Even with multi-channel support the audio channels are all via IAA rather than directly to a piece of hardware. I haven’t tested MIDI in via IAA with Audulus although I would expect it to work, and at this point there is no MIDI out. With the AU coming soon I’m not sure that multichannel I/O via IAA is a very high priority. I’m not sure exactly what kind of interaction with a modular you envision. One area I can’t comment on is whether IAA or AUv3 will pass DC signals through the audio chain. I don’t have an ES-8 (or modular) to test with. @biminiroad, can you test a CV output from Audulus to the ES-8 via IAA or the AU to see if it works?

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I am an AUv3 guy. If a plugin doesn’t have AUv3 I typically gloss over the other details and move on. In the case of Audulus I made an exception and I am glad I did. However, I would like to see the ES-8 be able to max out its capabilities with the iPad. Does this mean that control voltages can only be passed through two channels (ie., only one control voltage per channel); which would in turn take up the room needed to convert audio-in signals to digital recordable audio?

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Although I don’t know for certain, I expect the AU for Audulus will support multi-channel I/O. That being said, I can’t confirm whether any AU hosts will pass CV signals. In order for the CV signals to reach the ES-8 or other DC coupled I/O device, all the elements in the signal path would need to pass DC signals. I was able to confirm that AUM will at least receive a DC signal from Audulus via IAA, but since I don’t have a DC coupled I/O device, I can’t confirm that it will also output it. Even if AUM passes DC, other apps may not. Assuming for the moment that your AU host will pass DC, since you can run multiple instances of AU’s even if the Audulus AU was only two channels you could still effectively use more than 2. I believe that @biminiroad is currently testing the AU, so perhaps he can do some testing when he gets a chance.

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So, for me, two things hang in the balance…

  1. Can Audulus run as a plugin (whether as the current IAA or the coming AUv3) that is capable of transmitting control voltages back and fourth from user made modules through its host (preferably BM3, or at least Cubasis), on to the ES-8 and into a Eurorack.

It is good to hear that “AUM will at least receive a DC signal from Audulus via IAA,” but it would be nice to know if one can get a two way cv street going between Audulus and the ES-8 when running it as a plugin under a host like AUM.

  1. Channel limitations are as important as power limitations in my case and I am already looking at the expansion modules from Expert Sleepers as a way to future proof what I am doing. The hope is to never need the laptop, so I can be out in the boonies alone working on multi-day production sessions, but also have a capable live rig that is battery powered. I am close. The Eurorack needs to dovetail nicely with the current setup though.
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I wish I could be more definitive, but without an ES-8 or other DC coupled interface, I have no way to perform an end-to-end test. Hopefully @robertsyrett or @biminiroad will pick up our discussion and be able to comment at least as far as IAA is concerned. I know the AUv3 is currently in internal beta, but I don’t know if the feature set is finalized and if so, what it might be. I was able to confirm that I could send a DC or LFO signal from Audulus via IAA to BM3 and have it register on the BM3 VU meter. I then routed Beatmaker’s output via IAA to AUM and I still had a signal, so at this point it would seem likely that everything I can test is DC coupled. If I had to make a prediction, I would say that it is likely that it will also work with the ES-8.


That is some fantastic news. I am drawn to BM3 because it has that scene mode where I can make clips, then fire them and stop them at will. This is absolutely necessary for not loosing your audience when mucking around. BM3 still needs to tighten this mode up a little, but it looks like everything may come together over the next couple of years and I will be riding a nice wave of innovation.

It has always surprised me that you don’t have a Eurorack given your electrical engineering knowledge, digital/software knowledge, and love of playing music. My Dad is in the same boat. He says he stays away because its a rabbit hole. Funny though, he named his camp trailer ‘Alice’ and painted a bunny on the spare wheel cover.