ADDAC System 601 (–)
A hands-on, eight-band analog filterbank that turns sound into light, one voltage-controlled slice at a time.
Overview
If you've ever wanted to see your audio, the ADDAC601 VC Fixed Filterbank gets you closer than most. It doesn’t just filter sound—it dissects it, splitting any incoming signal into eight fixed frequency bands, each with its own volume, mute, and CV control. Built by ADDAC System in Lisbon, Portugal, this Eurorack module sits in the ADDAC600 Series and functions as both a precision sculpting tool and a dynamic CV generator. Plug in a drum loop, a synth line, or even field recordings, and suddenly you’re not just hearing the audio—you’re watching it move, band by band, as the individual outputs pulse with activity.
It’s an analog filterbank, which means the magic happens in the circuitry, not the code. There’s no digital conversion, no menu diving—just eight parallel bandpass filters, each locked to a specific frequency, letting you boost, cut, or completely silence slices of the spectrum with physical knobs and CV inputs. What makes it special is how much you can do with those bands: control their levels via voltage, mute them on the fly, route them individually, or blend them back into a full wet/dry mix. And if you need CV, each band doubles as an envelope follower, spitting out a control voltage that mirrors the dynamics of that frequency slice. That’s not just filtering—it’s real-time analysis.
Owners report it’s “a real beauty” and “a beast,” praise that feels earned once you start routing its outputs to modulate other modules. It’s been noted as functionally similar to the Verbos Electronics Bark Filter Processor, but in a smaller 20 HP footprint and at a lower price point—making it a compelling alternative for modular users who want that granular, spectral manipulation without dedicating half a rack to it.
Specifications
| Manufacturer | ADDAC System |
| Model | 601 |
| Type | Eurorack module, analog filterbank |
| Series | ADDAC600 Series |
| HP | 20 HP |
| Depth | 55 mm |
| Current Draw | 340 mA +12V, 250 mA -12V, 0 mA 5V |
| Filter Bands | 8 fixed frequencies |
Key Features
Eight-Band Spectral Control
The core of the 601 is its eight fixed-frequency bandpass filters. Each band isolates a specific slice of the audio spectrum, and you’ve got full manual control over the level of each via dedicated knobs. Mute switches let you silence any band instantly—perfect for rhythmic filtering or creating dynamic spectral gaps. The fact that each band has its own audio output means you can route individual frequencies to different effects, mixers, or modulation destinations. Want to send only the 1kHz component to a reverb? Done. Want to gate the 500Hz band with a sequencer? Go ahead.
Voltage Control and Envelope Following
Each band’s volume is managed by a linear high-performance VCA, meaning you can modulate the level of each frequency slice with CV. That opens up motion—think sweeping spectral contours, rhythmic pumping, or dynamic filtering locked to your sequencer. But here’s the twist: each band also acts as an envelope follower, with its own CV output. That means the 601 doesn’t just respond to your audio—it generates control signals from it. Feed it a snare, and the high-frequency bands output CV pulses that can trigger envelopes, clock delays, or modulate filters elsewhere in your system. It turns any sound into a modulation source, making it as much a utility module as a filter.
Flexible I/O and Signal Routing
You can feed two different audio signals into the 601—they’re mixed internally before hitting the filterbank. One input is optimized for synth-level signals, the other for line-level sources, and both have level controls, so you’re not stuck matching gear. The output options are where it gets deep: you can take the full processed signal, blend wet and dry, or tap into individual bands. There’s even a switch to route only the odd or even frequency bands to the main output, letting you create comb-filter-like textures or thin out a sound in precise steps.
Collectibility & Value
The ADDAC601 doesn’t have an original MSRP confirmed in the records, but current new pricing from retailers sits around $599. Used units have appeared in the market as low as €250 (as of January 2, 2026), while other merchant listings show prices ranging from $426.64 to $602.67. That spread suggests availability is limited and pricing is still finding its floor—typical for niche Eurorack modules with strong utility. Collectors and working modular users alike seem to value it for its dual role as both a sonic processor and a CV generator, especially given its functional overlap with pricier alternatives like the Verbos Bark Filter Processor.
There’s no data on common failures, maintenance needs, or long-term reliability—no reports of dying envelope followers or failing VCAs, but also no confirmation they’re bulletproof. Given its analog design and lack of moving parts, it’s likely stable under normal use, but power draw is substantial: 340 mA on +12V and 250 mA on -12V, so it’ll eat up a decent chunk of your power supply’s budget. If you’re building a system around spectral processing, the 601 is a smart centerpiece—but make sure your case can handle the juice.
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