ALM Busy Pip Filter ()

Name: ALM Busy Pip Filter
Brand: ALM Busy

A featherweight 4HP Eurorack filter that punches way above its size with pingable resonance and a built-in VCA.

Overview

Don’t let the tiny footprint fool you—this little slab of circuitry from ALM Busy Circuits is a fully functional 2-pole low-pass VCF with attitude. The Pip Filter packs voltage-controlled cutoff, manual resonance (capable of self-oscillation), a trigger input for pinging, and even a built-in VCA into just 4HP of Eurorack real estate. It’s the kind of module you slap into a case because you need a quick filter fix, and suddenly find yourself building entire patches around it. Designed as a compact solution for modular setups where space is at a premium, it doesn’t skimp on functionality—cutoff is controllable via front-panel knob, an attenuated CV input, or a unity-gain CV input, giving patchers flexible modulation options without needing extra utilities. The inclusion of a ‘ping’ trigger input means you can excite the filter for percussive pluck sounds, mimicking the attack of a plucked string or drum hit, all without an external envelope. And then there’s the VCA: integrated into the final stage and normally open, it lets you independently shape the amplitude of the filtered output, which is a rare and welcome bonus at this size.

What’s striking is how much is packed into such a minimal design. While it doesn’t offer the lush, sweeping character of a 4-pole ladder or the aggressive bite of a diode-based filter, the Pip Filter delivers a focused, responsive tone that sits well in a mix. The resonance control is smooth and musical, and when cranked, it breaks into clean self-oscillation—perfect for generating sine-like tones or adding harmonic tension to a sweep. The dual CV inputs for cutoff let you blend two modulation sources, say an LFO and an envelope, with one being attenuated so you can fine-tune its influence. That kind of thoughtful routing in a 4HP module shows ALM Busy wasn’t just trimming fat—they were optimizing. It’s not trying to be the center of attention, but in a system full of complex oscillators and sequencers, sometimes the quietest module is the one that holds everything together.

Specifications

Manufacturer	ALM Busy Circuits
Format	Eurorack
Width	4HP
Depth	32mm
Current	25mA @ +12V, 25mA @ -12V
Type	voltage controlled 2 pole low-pass filter with resonance, a ‘pingable’ trigger input and built in VCA
Original price	¥22,900 (tax-inclusive) / ¥20,818 (tax-excluded)
Current market price (MSRP)	$122 MSRP

Key Features

Compact 2-pole low-pass VCF design

At just 4HP wide and 32mm deep, the Pip Filter is built for efficiency. It’s the kind of module that fits in the gaps—those awkward 2–4HP spaces that seem useless until you realize you need a filter, fast. Despite its size, it doesn’t compromise on core functionality: it’s a fully voltage-controllable 2-pole low-pass filter, meaning it rolls off frequencies above the cutoff at 12dB/octave. That’s not as steep as a 24dB filter, but it’s plenty for shaping tone, taming brightness, or adding movement. The compact footprint makes it ideal for skiff-builders or anyone running low on space, and its modest power draw (25mA on both rails) means it won’t strain your bus board.

Flexible cutoff control with dual CV inputs

The cutoff knob is your primary tone sculptor, but the real magic happens when you patch into the two CV inputs. One is unity-gain, meaning a 1V input gives you a 1V response—perfect for linear modulation from sequencers or keyboards. The other is attenuated, letting you dial in how much of a CV signal affects the cutoff. This is incredibly useful when blending modulation sources: say you want a subtle LFO wobble on top of a strong envelope sweep. Patch the envelope into the unity input, the LFO into the attenuated one, and tweak the amount until it’s just right. No need for an external attenuator—ALM Busy put it right on the panel.

Resonance with self-oscillation

The resonance knob isn’t just for adding a little zing—it goes all the way to self-oscillation. Turn it up high with no input signal, and the filter starts generating its own tone, behaving like a sine wave oscillator. This is great for creating whistling sweeps, tuning the filter to a specific pitch, or using it as a secondary tone source in a minimalist patch. The transition into oscillation is smooth and predictable, which makes it musically useful rather than just a gimmick. And because resonance is manually controlled, not voltage-controlled, it’s stable and easy to set—though some users might wish for CV control, the simplicity keeps the design clean.

Trigger input for filter pinging

The trigger input lets you “ping” the filter—sending a short impulse that excites the filter core, creating a brief, resonant burst of sound. This is the classic way to generate plucked-string or drum-like tones without needing an external envelope or VCA. Just send a clock or trigger, adjust the resonance, and you’ve got a percussive element that tracks your cutoff knob. It’s simple, effective, and a hallmark of good filter design in modular synthesis. The Pip Filter’s ping response is snappy and articulate, making it a go-to for rhythmic textures.

Built-in VCA for independent amplitude control

Perhaps the most underrated feature is the built-in VCA in the final stage. It’s “normally open,” meaning if you don’t patch anything into the VCA CV input, the signal passes through unaffected. But patch in a gate or envelope, and you can control the amplitude of the filtered output directly. This means you can use the filter’s ping function for articulation while still having full dynamic control over volume—something many compact filters skip to save space. It effectively gives you a filter+VCA combo in 4HP, which is a rare bargain in Eurorack.