Focusrite Scarlett 18i20
Eight Focusrite preamps, ten line outputs, and a rack full of routing - the interface that made a project studio feel like a control room.
Overview
The Scarlett 18i20 was the flagship of Focusrite's USB interface line. The spec sheet shows why: eight microphone preamplifiers, ten analogue line outputs, and enough digital I/O to grow a small studio into a medium one without swapping the box. The name is literal - 18 inputs, 20 outputs. A two-in desktop interface makes you track drums in passes. The 18i20 lets you leave the kit miked up and still have channels left for overdubs.
The preamps are the headline. Focusrite's own marketing billed the eight onboard mic pres as "award-winning," touting the company's "legendary low noise, low distortion performance" paired with precision digital conversion. That's advertising copy, and it reads like it. Eight combo XLR/TRS inputs on the front and rear take microphones and line-level sources, and the front-panel gain controls feed a row of eight 5-segment LED bargraph meters. The meters read signal *after* the gain stage, so what you see is what the converter gets, not what showed up at the connector. The LEDs step through -42 dBFS (green, signal present), -18, -6, -3 (yellow), and 0 dBFS (red). Red means digital clipping, which you avoid, not chase.
The output side is where the 18i20 separates itself from cheaper siblings. It has ten analogue line outputs, all balanced on ¼" jacks. Outputs 1 and 2 are the main monitor pair, and 3 and 4 are the ALT pair. Outputs 5 through 10 are assignable, and the manual is explicit that they're electrically identical to the mains. That's enough to drive a 7.1 surround monitoring rig, send stems out to an outboard FX chain, or feed a headphone distribution system. The manual also walks through using the 18i20 as a standalone stage mixer for a keyboard rig, storing a Focusrite Control configuration in the hardware and running it without a computer attached.
Two features set the Third Generation unit apart: talkback and secondary monitor switching. The talkback mic is built into the front panel and activated by a momentary button. Press and hold, and the signal routes by default to the two headphone outputs, though Focusrite Control lets you send it anywhere. The ALT button diverts the main monitor mix from Line Outputs 1 and 2 to Line Outputs 3 and 4, so you can A/B your mix between two pairs of speakers from the front panel. When ALT is engaged, the manual notes, the outputs not in use are muted. That's fine until you need Outputs 3 and 4 for something else and have to go unmute them in software.
The digital section is comprehensive for the price class. Four TOSLINK connectors handle eight channels of ADAT at 44.1/48 kHz. In the Third Generation the optical ports also support Dual ADAT (S/MUX II) operation, delivering eight channels at 88.2/96 kHz. The left-hand port of each pair can alternatively be configured for two-channel optical S/PDIF. There's a BNC word clock output for syncing external digital gear, coaxial S/PDIF in and out on RCA, and standard 5-pin MIDI in and out, so the 18i20 doubles as a MIDI interface. A USB 2.0 Type-C port handles computer connection. At 176.4/192 kHz, the optical input and output are disabled. Keep that in mind before you plan a high-sample-rate multichannel session around ADAT.
Resolution tops out at 24-bit, 192 kHz, but only after you install Focusrite Control. Out of the box, the interface runs in MSD (Mass Storage Device) mode at sample rates up to 48 kHz, waiting for you to register and download the software. The manual offers a workaround: hold the 1-4 48V button while disconnecting and reconnecting the USB cable, keep holding for five more seconds, and the unit unlocks full functionality without registration.
Mix (July 2013, p.71) covered the 18i20 as a Pro Tools I/O solution, noting that input sources from the eight analogue inputs, ten digital inputs, and up to twenty outputs from the DAW are selectable via pull-down menus, and that Pro Tools I/O A 1-2 routes directly to monitors with speaker volume controlled from the front panel. That's the workflow the 18i20 was built for: configure it once in Focusrite Control, then forget the software and use the hardware. The same publication's advertising (October 2014, p.35) described the unit as the latest in Focusrite's USB range with eight mic preamps and comprehensive I/O including ten analogue line outputs, two independent headphone outputs, and S/PDIF and ADAT — the same feature set, stated plainly.
The front panel also has DIM and MUTE switches for the monitor outputs. DIM drops levels by 18 dB, and MUTE kills them outright. Both default to the main monitor pair but can be reassigned in Focusrite Control to act on any analogue output. Each has its own LED - yellow for DIM, red for MUTE. Two ¼" TRS headphone jacks sit below their own volume controls, and the headphone outputs always carry signal regardless of what the monitor section is doing. A green USB LED confirms computer recognition. A Locked LED confirms clock sync, whether to the internal clock or an external digital source. A MIDI LED blinks on incoming data.
The box ships with an IEC mains cable, a USB Type-A to Type-C cable, printed getting-started information, safety documentation, and a set of rack ears for mounting in a 19" rack. The warranty runs two years, valid worldwide, against manufacturing defects. That's generous for a product in this bracket, and worth remembering if you're buying used and wondering whether the original owner registered it.
The 18i20 asks for patience with Focusrite Control. The routing matrix is powerful - the manual's surround-sound section walks through mapping DAW outputs to line outputs one by one, and the standalone mixer section shows how to store a configuration in hardware - but it's not a plug-and-play device. What you get is an interface that behaves like a small console: eight preamps, ten balanced outputs, ADAT expansion, word clock, MIDI, and a talkback mic, all in a rackmount chassis.
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