An analog treasure-trove

Andrew Ostler ("Os") of Expert Sleepers

Expert Sleepers is no stranger to the eurorack world of modular synthesis, but Andrew Ostler (the man behind the curtain in Edinburgh, Scotland, UK) is known for his creations in the digital realm, not analog.

This is where it gets interesting.

Expert Sleepers' line of analog modules: a complete system, from a VCO to a Phaser - it's all here.

Hopefully, you're lucky enough to know Cocteau Twins. If not, you're welcome; I just changed your life. Seriously, listen to this band starting today. They are my favorite band of all time.

Andrew is enough of a Cocteau Twins fan to design a full synth voice with all its accouterments and name all the modules in the collection from tracks off Treasure, the Cocteau's 1984 release of the same name. Wow.

I highly recommend listening to Cocteau Twins: Treasure as you read this review of these modules. Go on. It will all make more sense.

Anyone who knows Andrews' (or "Os" as he's affectionately known) work ethic by his constant firmware updates for his digital modules will understand that if he's going to take on a project like this, it's going to be done right and in high quality. Still, most importantly, every module in this collection is going to have a twist to the classic original utilities. Os is gonna give each module some kind of killer upgrade - he's not going out plain vanilla, my friends.

So here we go..in album order, with words from Andrew ("Os") on how he put his magical twist on each module.

Also, I'll include some interview questions throughout. Enjoy. -JW

Ivo (The filter) The twist: "This is where it all began. It struck me as crazy that I’d been making modules for over 10 years and had never built what must surely be the most common analogue function, a filter. But I didn’t want to do that until I felt I had something genuinely new to offer - I didn’t just want to clone a classic design or use an off-the-shelf filter IC. So Ivo is a 2 pole lowpass filter capable of self-oscillation at high resonance, which is put together from two lowpass filter blocks and an allpass stage - all of which are built from discrete transistor OTAs rather than OTA chips - so it really sounds like nothing else."

MW: Having created so many amazing digital modules - what made you want to design this line of analog modules? Os: Two reasons really:

- traditional analogue synthesis is what got me into modular in the first place, and what I still go to first when using modular for music. I wanted to see if I could offer anything in that space that I love so much.

- digital fatigue! After the ES-9 and disting EX, I really fancied a rest from that style of design - very complex, but also strangely straightforward as you're just plugging building blocks together. The analogue stuff is much more of an art - a (usually) simpler circuit as the result but a much more iterative and exploratory design process.

Lorelei (The oscillator) The twist: "Lorelei takes the allpass filter design used in Ivo and uses them in a self-oscillating feedback circuit to create a true sine wave VCO. This means the sine output is a much purer signal than the “sines” generated by triangle- or ramp-cored VCOs. The two waveshaped outputs of Lorelei use folding techniques, which have the quirk that the pitch of the output appears to double at exactly 50% shape, which sounds cool when the shaping is modulated. The “X-mod” input is also unusual - while it’s similar to a familiar hard sync input, it’s different in that the behaviour of the sync depends quite markedly on the nature of the syncing signal, further widening the sonic possibilities on offer."

Beatrix (A phaser) The twist: "The last of the “first wave” of my analogue modules, Beatrix also uses the allpass filter block, but this time arranges a number of them in series to create a classic analogue phaser. It naturally has a unique sound due to the hand-rolled circuitry, but it also has an unusual “offset” control/CV which allows the phaser’s resonant peak and its filter notches to be swept independently."

MW: Tell us the connection with Cocteau Twins 'Treasure' and the naming of this collection of modules?

Os: I just love Cocteau Twins and that album in particular - which happens to have all one word song titles. Other Cocteaus titles like "Ella Megalast Burls Forever" wouldn't fit so well on an 8HP panel.

Persephone (The VCA/overdrive) The twist: "Apart from the headline “zero cross detection” feature, Persephone is unusual in that it uses a discrete JFET transistor circuit to control the gain, instead of an off-the-shelf VCA chip. This gives is a unique sound that in particular overdrives in a musically satisfying way. I’m aware of people who use a pair of Persephones as a master bus “flavour” processor, just to inject a little of that sound into the whole mix!"

Pandora (A bandpass filter w/ distortion) The twist: "Pandora’s a bit of an odd one. The germ of the idea was that of using a CMOS inverter (logic) IC as a high gain (analogue) amplifier, as in the classic EDP Wasp’s filter, but here I’ve done it with discrete power MOSFET transistors instead of the logic chip. These form a bandpass filter, much like that in an 808 kick drum circuit - which is why Pandora has that switch to drop the frequency range. And then of course it has vactrols, for extra flavour. I’ve made some wild rhythm tracks by feeding Pandora noise and a load of rhythmic CV modulation."

MW: What is the sequencer you'd choose to control this full voice?

Os: I very often use my FH-2 module in latched arpeggiator mode, in turn triggered from a Euclidean pattern (internal to the FH-2) to make the rhythm more varied.

Amelia (An ADBR envelope) The twist: "Amelia was designed to be particularly useful in a sequencer-driven patch, where you often have trigger pulses flying about but don’t have or don’t want to worry about an actual gate to define the note length. It generates its full envelope shape from a trigger - even if the attack is quite slow. The unique ADBR shape gives you a lot of control. It excels particularly at “plucky” sounds, where you have a fast initial decay and then a longer “ring” - not unlike that of striking a low-pass gate (the “Buchla Bongo”)."

MW: You created the amazing Disting NT. What's next for Expert Sleepers?

Os: It seems to be all disting all the time at the moment. What I seem to have created with the NT is a platform - for my own ongoing development, but also for everyone else, now that it has Lua scripting and a C++ API. People have already created some amazing stuff for the NT - it's turned into quite the ecosystem. See for example: https://nt-gallery.nosuch.dev/

Aloysius (An AHDW envelope) The twist: "In a wonderful bit of serendipity, there are two adjacent “A”s in the naming scheme for these modules, and Aloysius took the core of Amelia and became something inspired by the EMS Synthi’s trapezoid generator. It’s an extremely flexible source of modulation - especially in “free-running” mode when controlling all the various stages with CV."

Cicely (An octave/fuzz) The twist: "I was made aware of the Octavia pedal by my long-standing musical collaborator Mike (our band is called Darkroom - look us up!). It’s a particular favorite of his. As with many of these vintage ‘60s pedal designs, it’s fundamentally a really simple circuit - but of course, not voltage-controllable. So the challenge here was to make it CV-able and therefore useful in a modular context. I love how this module adds grit to the sound. So many great electronic timbres are low-pass filtered - and who doesn’t love a classic VCF - but that can leave them lacking in top end."

Otterley (The multi-LFO) The twist: "By the time I did Otterley it was becoming apparent that this analogue range had almost become a complete “system” by itself, which was never really the intention. The one thing lacking in such a system was LFOs, so Otterley satisfies that need. The idea of “spread” is one I’ve used many times in the past, going right back to my VST plug-in products. It’s a really convenient way of controlling multiple things at once with one parameter/knob/CV. There’s a lot of fun to be had with Otterley by patching it for self-modulation."

MW: Anything on the musical horizon for you as an artist?

Os: I've just recently released a new album with my band The Shell

https://the-shell.bandcamp.com/album/the-shell, in which, by the way, I'm not the synth player - I'm the saxophonist! I do have a Disting NT on my pedalboard, though.

This is taking up much of my music energy at the moment, though I do have plans for a follow-up to my last solo album, The Blind Sublime. I want to get back to some real first-principles synthesis (using my own modules, no doubt!), some seriously electronic tones - but will probably retain at least some of the orchestral and choral timbres as well.

Visit the Expert Sleepers website for more info and also to purchase these modules!

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"An analog treasure-trove", by Johno Wells, August 2025