Thursday, Jun 13, 2019

Modern filter designs

In recent years, the complexity of individual Eurorack modules has increased significantly, and more and more functions are behind ever smaller front panels – although here, too, the rule is confirmed by exceptions. The fact that Doepfer, for example, is now putting on a “Slim Line Series” seems to confirm this assumption.

One reason for this trend is certainly the search by musicians for the highest possible functionality in a small space – Eurorack cases may have become cheaper, but space in the rack is still valuable. This is also where the fact comes into play that many musicians want to be mobile with their system or that space in the (home) studio is simply limited.

But now to the actual topic: In the last few months a few filter modules have stood out in particular, which somehow follow the development described above. These filters are basically neither bigger nor smaller than other filter modules, but they add a high degree of flexibility to the classic filter design. For example, they can blend between different filter types, offer Q compensation, saturation levels, many CV control options, as well as well-chosen parameters and sophisticated sound aesthetics. These features are all not new, but to see more and more filter modules offering these possibilities, gives the impression of a new “standard” of what a filter should be able to do.

In the following I will discuss three modules:

Altar by Ritual Electronics

Dendrites by River Synths

Filter Threek 13700 by Funkstill

ALTAR has an unusual morph between BP-LP-HP and is very good at keeping a constant level. It has a slope steepness of 18dB and very well designed saturation.

The second module of the French manufacturer Ritual Electronics was given the name Alter. It is characterized by the fact that the different filter modes (BP-LP-HP) can be blended by a dedicated knob and CV. No new feature, but one that is not as common as one wish. The edge steepness of 18dB is also relatively rare, which gives this module a well-balanced middle way between Oberheim softness and Prophet 5 punch. The possible saturation of the input signal by asymmetric clipping as well as the powerful and always musical resonance contribute to this.

All in all, this complex filter module feels like a coherent whole. At no time you ask yourself why the manufacturers didn’t work on the parameter ranges here and there, or why they didn’t add another CV input – because everything was thought of here. A big, flexible and distinct sound meets a tidy front panel, which can be enjoyed by beginners as well as experts.

DENDRITES truly is a clever experimental toolbox. It really has its own sound. Vintage, but clear.

The next candidate was developed in the Netherlands and is much more complex than Alter, but still very manageable. The River Synths Dendrites features 16 filter modes, three different resonance modes and two overdrive modes behind a very compact front panel. Together there are 96 combinations of these three ingredients. But you don’t have to worry about losing control, because the central control element allows you to switch between the filter modes while providing nice visual feedback. Equipped with an LED ring, Dendrites shows you which filter characteristics the circuit is currently dedicated to – among them various low-pass, bandpass and high-pass filter types, as well as two phasers and four mixed filter types.

Further adjustments to achieve the desired sound aesthetics can be made with two switches and the input gain. Especially the adjustment of the resonance behavior is to be emphasized here – with it the character of the Dendrites can be changed drastically. K-Style stands for a classic, aggressive style that one is used to from old Korg synthesizers. Vintage stands for a rather soft and round, stronger coloring behavior. Q-Comp regulates the relationship between filtered audio signal and resonance and ensures a different presence. The Dendrites is thus up to almost any task, always sounds high-quality and offers additional extras like switchable FM, i.e. linear and exponential FM.

FILTER THREEK 13700: Strong references to its role model, the Oberheim Matrix Filter (which in turn is a further development of the Oberheim SEM).

Not only does the Filter Threek 13700 by Funkstill have a slightly more complicated name than the previously described modules, it also offers a more complex circuit and user interface. Here you can really get deep into the signal path – which of course increases the possibilities this module offers, but also results in a steeper learning curve. So much for starters – the Threek 13700 filter wants you to get its attention, but it also rewards the user with wide spectral possibilities and complex morphing.

Funkstill has implemented two filters – two serially linked multimode circuits. The first stage can be operated in a high pass, bandpass, low pass or all pass mode with a slope of -12 dB per octave. The second filter is a high pass or low pass circuit. The slope here is -6 dB per octave. The combination of both stages makes all kinds of complex filter shapes possible. Thanks to the 2-pole output and 1-pole input, it is also possible to use the filters individually. Resonance is available in two very different variants, Q-compensation is also implemented – this way you can counteract the loss of bass frequencies with increasing resonance values.

What is the bottom line? It requires training, but is also a real studio/sound design tool – perhaps on the level of the Rossum filters.


This is by no means a full review of these modules – this text and he short videos are only there to get an impression of what to expect from these versatile modules.


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