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Modbap Modular Meridian

Eurorack Module By William Stokes
Published December 2023

Bela GlissModbap Modular’s Meridian is a dual digital filter ‘array’ that can switch between an array of modes and signal path configurations. It also offers a dedicated Ping input, nestled between a brace of onboard effects; a drive that also boasts a dark, digital lo‑fi side; and a panning variable‑speed phaser. It’s an impressively compact module considering its functionality, just 14HP wide, but there’s big sound‑sculpting potential here. With the ability to operate in either the mono or stereo realms to boot, it’s primed for a wide and enjoyable range of applications. You’re not going to find any old‑school, purist circuits here...

The Meridian presents a neatly sized panel with three main knobs: two for the cutoffs of the two filters (with resonance pots) and one large central knob labelled Prime Freq. This is ostensibly a means to control both of those together — though its function deviates from this in certain modes, which I’ll come to shortly. Above these at the top of the panel is a row of buttons and multi‑coloured LEDs for choosing the signal routing (series or parallel) and image (stereo or dual mono), but more pertinently the filter mode and filter type.

‘What’s the difference between a filter mode and a filter type?’ I hear you ask. Well — at least, by the Meridian’s rubric — the modes consist of Low Pass, High Pass, Band Pass and Notch. The filter types, on the other hand, consist of Ladder, OTA, Comb and Vocal Formant. You may notice that these types don’t all technically fall into the same category. Strictly speaking, the latter two should be included alongside Low Pass, High Pass and the like, but here it doesn’t seem to matter. The takeaway is that any mode can be paired with any type.

The ladder’s response is certainly the most ‘classic’ of the two, it being based on the kind of longstanding filter design found in Moog synths; while the OTA (Operational Transconductance Amplifier), a favourite of classic Japanese synths, has a slightly more watery, harmonically complex sound to my ear, with the difference between the two of course more audible upon cranking their respective resonances. Both of these are fixed at a four‑pole, 24dB‑per‑octave slope.

Fair to say that, in their purest form, the sound of these filters left me wanting. While they could reach decently resonant self‑oscillating territory, they don’t match the kind of smoothness or, at the other end of the spectrum, squealing analogue attitude associated with many of the filters listed above, nor do they track at 1V per octave. I also noticed the occasional value jump from time to time. Don’t get me wrong: what’s on offer here performs well but, when it comes to filtering for filtering’s sake, not exceptionally.

Luckily, filtering for filtering’s sake seems not to be particularly high on the agenda for the Meridian. It’s not the only feature on the panel, after all. The Comb and Vocal Formant filter types are excellent — particularly the Comb. Rich and bell‑like, particularly in their ‘sweet spots’ at high resonances, for these types the central Prime Freq knob changes its function to become an independent, state‑variable 12dB‑per‑octave filter. Chiming, morphing sounds and textures were achievable even with the simplest of source audio. Parallel or serial routing, stereo or dual mono; each had their own character to offer and brought out different facets of the dual‑filter workflow for a veritably three‑dimensional experience.

Below is the effects section, in the middle of which is nestled the Ping input and attenuator. This, I will say, is brilliant, and I’m now of the view that every filter should have one. It is of course possible to Ping any filter, provided it can self‑oscillate sufficiently, but the Meridian’s dedicated input, which ostensibly triggers a low‑pass gate, allows the filter to be excited percussively by gate signals and adds an entirely new dimension of movement to the filtered sounds. It’s also possible, using the Meridian with a sequencer, for example, to send the sequence triggers to the Ping input (instead of the usual cutoff CV input via an envelope) and keep the other cutoff CV inputs available for more inventive modulation. Since the LPG’s decay time is adjustable, it’s easy to achieve a modest range of musical, envelope‑like responses, too. Clever.

Even if you already possess several filters, the Meridian is bound to bring something unique to your system.

The drive and phaser sections impart further sonic depth; by now it feels like it wouldn’t be a Modbap module if there wasn’t some way of crushing a signal to echo the lo‑fi digital vibe of samplers of yore. This the Meridian does nicely, and even at low settings allows for some detailed harmonic sculpting. This feeds nicely back into the overall sonic signature of the module, since it’s placed before the filter circuit in the signal chain. The phaser circuit is smooth and warm, surprisingly so, and incorporating its panning utility with the Meridian’s overall stereo goodness made for some gorgeously wide and lush processing. It can even touch audio rate as well, which, combined with the Speed CV input, made for some brilliant experimentation.

To me, Modbap’s designs are effusive and generous, and the Meridian is no exception to this. It’s true: on paper there are more finely tuned options out there when it comes to filtering per se, but the architecture of the Meridian, the way it arranges its elements, is such that it seemed to take on a more holistic sound shaping, even sound generating, role in my patches — to the point where simply calling it a ‘filter’ feels a little unjust. If you’re looking for a classic, reliable, analogue‑style filter, then I daresay the Meridian isn’t for you. Plus there are a litany of those out there. But there isn’t much like this. Even if you already possess several filters, the Meridian is bound to bring something unique to your system.