Any module that can add expressiveness, bring more performative and humanizing aspects to a rack is very welcome, and 4ms' new Percussion Interface and expander modules [sold together as a unit] do just that. At its core it is an envelope follower and envelope generator but the Percussion Interface has some really smart features that make it a very versatile and easy to use unit, and the modules are aimed at integrating live drums and other percussion with your Eurorack system [although any audio source will work].
The PI comes as two 4hp modules; the main interface and an expander module. The main module has a large SENSITIVITY knob which controls the boost level of the input signal and is integral to dialing in the desired behavior from the PI. You’ll have to tweak this knob a lot, depending on your signal source and its dynamic range.
The SENSITIVITY knob has a variable range itself, which is determined by the position of the L|M|H switch on the PI Expander. The knob’s LED provides some visual feedback by going from blue—for signal detection—to red, when the input begins to clip. Adjusting the SENSITIVITY along with the gate SUSTAIN can be a bit finicky at first but is key for avoiding firing off unwanted gates. Depending on say, the length of a bass drum decay or a more complex audio source [speech for example], if you don’t adjust the PI correctly you’ll get every response you can imagine, from barely a gate to a chaotic onslaught of pulses.
There are mini pots for SUSTAIN and ENVelope DECAY, and the SUSTAIN knob adjusts the width of the generated gate. Again here, you have to fiddle with these in tandem with the SENSITIVITY knob in order to get your gates to fire as you'd like, and it's easy to misdial this combo at first, but there is a lot of helpful information in the included manual addressing best settings for various sound sources.
The unit has a switch to choose between envelope FOLLOWing or envelope GENeration. When GEN is selected a consistent envelope will be generated regardless of the audio. The attack and sustain portions of the GENerated envelope mirror the gate with a vertical attack portion and a sustain as wide as the pulse width of the gate. How often is dependent on the sensitivity settings [did I mention that you have to adjust those?]. When in FOLLOW mode the PI will, ahem, follow the amplitude of the input signal and allows for much more nuanced and interesting envelope shapes. This is the go to mode for experimenting with acoustic percussion sources. A single microphone over a drum kit will work and as long as you spend the time to tweak those input settings, you can really transfer some dynamics at the kit to dynamics in your rack.
Further down the main module, there is an INput jack for the audio source [this one is 3.5mm] and outputs for GATE, and both the regular envelope and an inverted copy. The expander module features attenuator control over the levels of both the ENVelope and its INVersion, and as mentioned above, there is a 3-way toggle switch for different input gain settings [low, medium, high], two additional envelope outputs [one positive and one inverted], an Audio output, and a 1/4" Input.
If micing up a drum kit sounds like the last thing you’d like to do when patching up your modular rig, don’t fret, as it’s just as easy to work with other sound sources. The 1/4" input jack makes it super convenient to patch in external microphones and other audio gear without having to search for an adapter, though it should be noted that only one audio input can be used at a time, with the 3.5mm input jack on the main PI module taking precedence [patching into the main will disable the 1/4" jack on the expander]. The expander module's audio output jack also allows the PI to also be used as a preamp to bump external signals up to modular levels. Handy!
Aimed primarily at those looking to drum along to their system or otherwise incorporate acoustic percussion control sources into their racks [and it is undeniably a ton of fun to drive a sequencer from an acoustic drum kit], the PI readily works with any audio source and offers a really interesting and easy way to experiment with any other external equipment you have. Synch up some modular modulation with an external drum machine or sampler, modulate a filter with an ambient recording of a crowded bar, FM an oscillator by tapping your fingers on a table; the only limit to what you can feed the PI is your imagination. Once you figure out how to get the input settings working for you, the PI becomes an excellent vehicle for putting the play back into playing with synths.
Who would I recommend the Percussion Interface to? If you are a drummer, get it. If you've always wanted to tap along with your patches or are looking for a fun way to integrate other sounds sources or audio equipment into your rack, get it. Are you on the fence and can't imagine what you'd do with the PI and can't see a use? Get it and be surprised at how much fun you're having with your system again.
4 HP each
+12v 104mA -12v 65mA
Price: $165 [for both]

4ms.com