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Euterpe Vertice

Hand-built Analogue Filterbank By Rory Dow
Published April 2020

Euterpe Vertice

They say they don't make 'em like they used to, but in the case of this Italian boutique filterbank, they do!

The Vertice Seconda Serie is an analogue 'filterbank' built as if it were 1975. I know this because creator Stefano Bersanetti sent me a foam board with a selection of the authentic '70s components he uses in every build, each one more chunky and colourful than the next. He is rightly proud of his through-hole and hand-soldered circuit boards, which are a work of art in themselves, and this passion for retro quality is evident in the front-panel design too, with chunky Bakelite knobs, switches which wouldn't look out of place on a submarine, chrome carry-handles, hand-crafted wooden end-cheeks and 'proper' quarter-inch jack sockets for inputs and outputs. Even the orange-on-brown panel printing will have you wondering if you've stepped back in time. The look and feel of the Vertice, then, promises something quite special in the sound department. Does it deliver?

Three Is The Magic Number

In the best tradition of analogue filterbanks, the Vertice is built around three multi-mode 12dB/octave filters which can be arranged and modulated in different ways. The filter circuit is a customised Sallen-Key filter originally created by Nyle Steiner back in 1974, and most famously used in the Steiner-Parker Synthacon. It's a filter known for its lively, unstable resonance, and a fine choice for a 'character' unit. An interesting addition to the circuit design is a switch to change the resonance (referred to on the panel as 'emphasis', for purely historical reasons). The natural resonance of the Sallen-Key filter is Diode mode but there's also a Transistor mode here, switchable per filter. It's always difficult to describe resonance characteristics, but I think Transistor mode offers a meatier, more metallic body. Diode mode can be much more shrill, and disappears into ultra-sonic frequencies more easily. Both sound fantastic, especially when you overdrive the filter inputs.

Euterpe have gone to great lengths to make the Vertice sound vintage — including using original 1970s components where possible.Euterpe have gone to great lengths to make the Vertice sound vintage — including using original 1970s components where possible.

Each filter has a set of controls at the top of the unit, comprising cutoff frequency, emphasis (resonance) and a low-, band- and high-pass switch. As well as each filter's frequency control, there's a large master control which offsets all three at once. The three filters can be configured using a series of switches to create serial, parallel or stereo routings, which appear at both a pair of mono outputs and a stereo headphone output. The main two outputs are mirrored on the front and back of the unit. The back also offers direct outputs for filters A and B, and an envelope output. The manual suggests wiring these to a patchbay, and it's good advice, especially if you're rackmounting the unit, as you'll be using these for all sorts of routing and feedback tricks.

There are three dedicated audio input jacks, one for each filter, and a control to vary the gain. The input preamplifiers can be overdriven (around +17dB on a common line-level signal) to achieve a lovely, crunchy overdrive going into the filters. If you desire more of that delicious drive, the overdrive switch engages a distortion circuit for the input of Filter A, a dramatic distortion which adds up to +40dB to a line signal. It only works on the first filter, so it won't be of any use if using the Vertice in stereo configuration, but with a serial setup it's perfect, as the overdrive is at the start of the filter chain. There's further distortion to be had by overdriving the output VCAs. The large 'staccato/continuo' knob controls the output amps for the two main outputs, and will happily add even more lovely, analogue distortion. If you require stereo distortion, this is how you add it, and you can also use a CV signal at the AM input to push the VCAs even further into distortion than the knob will allow. In short, if you like analogue overdrive and distortion, the Vertice has you covered.

The front panel includes plenty of means of controlling the filterbank, including via CV inputs.The front panel includes plenty of means of controlling the filterbank, including via CV inputs.

CV Baby

A filterbank is nothing without animation and movement and the Vertice offers plenty of CV inputs along with a loopable, ADSR envelope. Each filter has a dedicated frequency CV input with attenuator and there are two CV inputs for the master frequency control, one with an attenuator and a V/Oct input. The manual warns you that this input is unlikely to give you perfect chromatic tracking of frequency, and in my tests with a perfect V/Oct signal I could get no more than a few semitones of accurate pitch tracking; as the manual says, "Do not expect perfect musical intervals correspondence." Nonetheless, it's a bonus CV input for the master frequency, and can be used to sum two CV inputs.

The ADSR offers another useful way to add interest. It's triggered by either the panel-mounted trigger button or the EG Gate input, which accepts 5V triggers and gates. In addition to the attack, decay, sustain and release controls, three speed settings (percussive, smooth and slow) change the envelope stage lengths. By feeding audio signals to the EG Gate input and setting the envelope speed switch to either smooth or slow, I was able to get something approaching an envelope follower. There are also switches to invert and loop the envelope. The envelope can be switched to control either the master filter cutoff or the output VCAs. But if you patch the rear-panel envelope output into the Amplitude Modulation input on the front, and set the envelope to modulate VCF, you can modulate both VCF and VCA at once — though they'll still both be controlled by the same EG Level control.

This is an instrument built with passion. I would challenge anybody with a fondness of analogue processing not to fall in love.

Scenarios

Let's consider a few scenarios. The first thing you're likely to do is patch some audio signal into the Filter A input and try out a single filter. Even in this most basic configuration, the quality of sound is noticeable. With no resonance and a low input gain, the filter is clean whist still imparting some analogue magic. This unit doesn't have a bypass, so whatever you put through it will always be processed to some extent, even with modest gain levels, and filters wide open.

The next step is to chain the other filters in series, in which scenario you'll probably have Filter A going into Filter B and on to Filter C. Combining different filter types, frequencies and resonance together in this way gives a huge range of tone-shaping options. For example, you can create your own variable-range band-pass by chaining high- and low-pass filters together, and using the master frequency to move this band. Or you can stack three filters at the same frequency to create a 36dB/octave response.

For the stereo configuration you need to feed signals to Filters A and B, enable the correct switches, and monitor the two outputs. This is fine if you want to process a signal which is already stereo, but if you wish to generate a stereo output from a mono signal, you'll need to duplicate the signal before patching it into the device, giving you one version for each input. It would have been nice if, when stereo mode was enabled, the audio input at Filter A was normalled to the Filter B input (until you insert a jack). Nevertheless, stereo processing proved to be equally rewarding. Even with a (multed) mono signal, simply setting the two filters to equal settings gives a gorgeous sprinkling of stereo mojo.

My next adventure was to investigate the gain staging more closely. With multiple amplifiers to overdrive, and the overdrive switch for Filter A, there's plenty of potential to roughen up a signal. And what a delight! I pulled my Boss DR-110 drum machine off the shelf, fed it to the Vertice, and with the input amp cranked up to full, the DR-110's already bass-heavy kick drum turned into a big, beautiful monster. But engage Filter A's overdrive and the magic really kicks in. Full drum loops sounded superb — smashed to bits, but totally coherent; there wasn't a hint of nasty clipping or unpleasant distortion, just oodles of unbridled analogue overdrive of the highest calibre.

Getting some modulation involved seemed like a natural next step, so I connected the DR-110's accent output to the envelope gate input; this way I could trigger the envelope in time with the DR-110's sequencer. This worked like a charm, and by setting appropriate envelope times I was able to get smooth filter-automation pumping nicely with the ingoing loop. The envelope stages are capable of a wide range of times, from short and snappy to somewhere in the region of a minute, with all stages set to their longest times. Combining triggers and the loop function was a nice way to get well-timed rhythmic effects.

Switching the envelope to controlling VCA level can cause extremely high volume levels and, as those analogue VCAs distort so nicely, this can be used to great effect to cause rhythmic distortion and volume changes. Inverting the envelope means you can effectively side-chain an incoming signal (with amplitude or frequency).

The main two outputs on the rear duplicate those on the front, but you'll also find direct outputs from filters A and B here, as well as an envelope output.The main two outputs on the rear duplicate those on the front, but you'll also find direct outputs from filters A and B here, as well as an envelope output.

Of course, envelopes aren't the only modulation sources, so I drafted in some LFOs and sequencers from my modular system. As I expected, the Vertice handled them all with style. The filter-frequency CV input can handle up to ±10V without a problem, and coped easily with any signal I could muster from my Eurorack setup. Using audio rate modulation proved equally fun; an endless source of additional side-band frequencies, ring-modulation(ish) and general craziness is possible when employing other sources of CV and audio.

A final thing to mention is that the Vertice makes an excellent three-channel summing box, or a stereo-plus-mono sum, where Filters A and B are your stereo sides, and Filter C is your mono signal. Even with minimal processing, the Vertice will add analogue charm to any signals you put through it. My experimentations continued with combining various instruments, bass, vocals, synths and so forth, and the summing, filtering and distortion possibilities proved to be nothing but a pleasure.

Conclusion

In the sound department, the Vertice is exactly what you'd expect — the genuine article, a filterbank built in the best traditions of the golden age of analogue, using, as far as possible, original components from that era. The emerging sound is rich, full, creamy, crunchy think of your own favourite analogue adjective and it's probably that too.

The design, philosophy and build quality are also superb: it's an instrument built with passion, and I would challenge anybody with a fondness for analogue processing not to fall in love. The analogue overdrive is sublime and the filters feel like the smoothest things on earth. It's pure vintage analogue bliss. But it's not just about the sound. Every switch is satisfying to use, every knob is smoother than butter, and has just the right resistance to bring even minute filter tweaks utterly under your control. The design and build is second to none.

Of course, such words of praise mean there's an inevitable sting: the Vertice will set you back a teeth-sucking €1990. For that money, you're not really getting lots of features: three filters, an envelope and a smattering of VCAs. But you're paying for something else. There are other filterbanks at half, or even a quarter of this price, which will win on features, and of course I'd love the Vertice to have an envelope follower or an LFO. But the Vertice offers a total lack of compromise where sound is concerned. It's a truly artisan instrument, a highly desirable, make-stuff-sound-better box in all the best ways. If I sound a tad smitten, it's because I am!

Alternatives

The Niio Analogue Iotine Core 4 and Sherman Filterbank are probably the closest filterbanks currently in production. The Iotine Core 4 also has three filters, whereas the Sherman has two. Both offer more modulation sources, such as envelope followers or LFOs but, in my humble opinion, neither hits quite the same analogue-mojo heights as the Vertice.

Shout Out To The Manual!

Euterpe deserve credit for the manual that accompanies the Vertice — it's a treasure trove of background information, circuit-design debate, technical specification, witty one-liners and patching tips. Not only was it a worthwhile read, but it even made me laugh out loud on occasion. That's not something you often get to say about any manual!

Pros

  • Triple multi-mode filters with flexible routing options.
  • Not just a filterbank, but a distortion and summing box.
  • Beautiful build quality with a sound to match.
  • Buckets of analogue mojo.
  • Genuine '70s design and components.

Cons

  • Not as many modulation sources as other filterbanks.

Summary

This is a beautiful filterbank, distortion unit and summing box, hand-built in Italy using nothing but the best vintage components. It sounds superb and you should want one!

information

€1990 including VAT.

euterpesynth.com

€1990 (about $2150).

euterpesynth.com/

Published April 2020