ADDAC System 601 (–)
A hands-on, eight-band analog filterbank that turns sound into light, one voltage-controlled slice at a time.
Overview
The ADDAC601 VC Fixed Filterbank splits any incoming signal into eight fixed frequency bands. Each band has its own volume, mute, and CV control. ADDAC System builds it in Lisbon, Portugal. It's a Eurorack module in the ADDAC600 Series, and it works as a sculpting tool and as a CV generator. Plug in a drum loop, a synth line, or field recordings, and the individual outputs pulse with activity, band by band.
It's an analog filterbank, so the work happens in the circuitry, not in code. There's no digital conversion and no menu diving. You get eight parallel bandpass filters, each locked to a specific frequency, and you boost, cut, or silence slices of the spectrum with physical knobs and CV inputs. You can control band levels via voltage, mute them on the fly, route them individually, or blend them back into a full wet/dry mix. Each band also doubles as an envelope follower, putting out a control voltage that mirrors the dynamics of that frequency slice. That makes it real-time analysis as well as filtering.
Owners report it's "a real beauty" and "a beast." 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.
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 dedicated knobs give you full manual control over the level of each. Mute switches silence any band instantly, which suits rhythmic filtering or dynamic spectral gaps. Each band has its own audio output, so you can route individual frequencies to different effects, mixers, or modulation destinations. Send only the 1kHz component to a reverb, or gate the 500Hz band with a sequencer.
Voltage Control and Envelope Following
Each band's volume is managed by a linear high-performance VCA, so you can modulate the level of each frequency slice with CV. That allows sweeping spectral contours, rhythmic pumping, or dynamic filtering locked to your sequencer. Each band also acts as an envelope follower, with its own CV output. So the 601 generates control signals from your audio as well as responding to 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, which makes 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, and they're mixed internally before hitting the filterbank. One input is optimized for synth-level signals, the other for line-level sources. Both have level controls, so you aren't stuck matching gear. For output, you can take the full processed signal, blend wet and dry, or tap individual bands. A switch routes only the odd or even frequency bands to the main output, which gives comb-filter-like textures or thins 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. Collectors and working modular users seem to value it 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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