As an Amazon Associate I earn from qualifying purchases. This write-up is based on manufacturer specifications and published documentation, not hands-on testing.
The Focusrite Scarlett 18i20 (4th Gen) is a 1U rack interface with eight mic preamps, ten line outputs, two headphone outputs and ADAT expansion, built for recording full bands and drum kits. It is the flagship of the Scarlett 4th Gen range and needs external power.
Key specs
| Mic preamps | 8 mic/line preamps, up to 69 dB gain |
| Instrument inputs | 2 front-panel instrument inputs |
| Outputs | 10 line outputs (main and alt speakers plus 6 more), 2 independent headphone outputs |
| Digital I/O | 2 ADAT ports, S/PDIF, word clock |
| Other | MIDI In/Out, built-in talkback mic, loopback |
| Max I/O | Up to 26 in / 26 out |
| Resolution | Up to 24-bit/192 kHz |
| Power | External power supply (not bus-powered) |
Who it is for
- Engineers recording drums with six to eight mics.
- Small studios needing two headphone mixes and a talkback mic.
- Anyone planning to expand with an ADAT preamp for 16+ mic inputs.
Strengths
Eight 69 dB preamps cover nearly any mic. Separate main and alt speaker outputs let you switch between monitors. Two ADAT ports allow up to 16 extra channels at 44.1/48 kHz from external preamps.
Limitations
- Not portable or bus-powered.
- ADAT channel count drops at higher sample rates.
- Overkill if you record one vocalist at a time.
Check the Focusrite Scarlett 18i20 4th Gen on Amazon
Inputs and outputs in practice
Focusrite lists eight mic/line preamps, two of which on the front panel also accept instruments through Hi-Z inputs with a 1 MΩ impedance. The remaining six preamps sit on the rear. Eight preamps cover a typical drum kit, for example kick, snare, two or three toms, a pair of overheads and a room microphone, or a small live band with several sources at once. Two ADAT ports add up to 16 more channels at 44.1 or 48 kHz from external preamps (dropping to eight at 96 kHz), and S/PDIF adds two more digital channels, which is how the interface reaches its 26-input count.
On the output side, Focusrite lists ten balanced line outputs, including main and alternate speaker outputs, plus two independent headphone outputs. Those extra outputs let you feed separate headphone mixes through external amplifiers, route signals to outboard compressors or effects and back, or connect a second set of monitors for comparison. The built-in talkback microphone lets an engineer speak to performers through their headphones without a separate microphone.
Published specifications explained
The mic preamps offer a 69 dB gain range with −127 dBu EIN (A-weighted) and a maximum input level of 16 dBu. The line outputs are rated at 122 dB dynamic range (A-weighted) with a maximum level of 16 dBu, and the headphone outputs at up to 57 mW into 33 Ω. In practice, 69 dB of gain is enough for low-output dynamic and ribbon microphones without extra boosters, and the headphone amplifiers are designed to drive high-impedance headphones. Conversion supports sample rates from 44.1 to 192 kHz at 24-bit.
Auto Gain, Clip Safe and Air
As part of the 4th Gen range, the 18i20 includes Auto Gain, which listens to a source and sets preamp levels, and Clip Safe, which reduces gain automatically if a signal is about to clip. Both are useful when tracking several musicians at once, when one engineer cannot watch every level. The Air feature offers two modes: Presence, which lifts the high end, and Presence and Harmonic Drive, which adds midrange harmonics. These are applied at the input, so they are recorded with the signal.
Remote control and routing
Focusrite Control 2 manages routing, headphone mixes and preamp settings on Windows and macOS, and a mobile app for iOS and Android can control the interface remotely. This is handy when you are in the live room setting up microphones and need to adjust gain without walking back to the computer. Loopback lets you record computer audio, which helps when streaming or capturing audio from other software.
Physical design and power
The 18i20 is a 1U rack-mountable unit, supplied with rack ears, and Focusrite lists it at around 3.3 kg. It is not bus-powered and uses an IEC mains power cable, so it is designed for a fixed studio rather than portable recording. It connects over USB-C using the USB 2.0 protocol and supports word clock for syncing with other digital devices.
Who should look elsewhere
If you record only one or two sources at a time, a smaller interface such as the Scarlett 2i2 or 4i4 is easier to carry and set up. If you need more than 26 channels or very large routing setups, consider a networked audio system or a larger interface range.
Setup checklist
- Install Focusrite Control 2 and any firmware updates.
- Rack-mount the unit or place it on a stable surface with ventilation.
- Label each input channel in your DAW before a multitrack session.
- Set up headphone mixes for performers in Focusrite Control 2.
- If expanding with ADAT, set the external unit to follow the 18i20 clock or vice versa.
Example drum input plan
| Input | Source |
|---|---|
| 1 | Kick |
| 2 | Snare |
| 3 | Rack tom |
| 4 | Floor tom |
| 5–6 | Overheads (left and right) |
| 7–8 | Room microphones or hi-hat and bass DI |
Keep this layout consistent between sessions so templates and routing work every time.
For larger sessions, an ADAT preamp such as an eight-channel unit can add more microphone inputs for extra room microphones, a second snare microphone or additional instruments, while the 18i20 remains the clock and routing hub.
A quick test with an ADAT expansion: route its eight channels to new tracks, record a few seconds from each, and confirm there are no clicks before a real session.
How to set up the Focusrite Scarlett 18i20 4th Gen
The 18i20 has a lot of I/O, so a planned setup saves time. Focusrite’s Scarlett 18i20 product page links to Easy Start, downloads and the user guide.
1. Mount and power it
The unit is 1U and ships with rack ears, so it can sit on a desk or in a rack. It is not bus-powered. Focusrite lists a 30 W external supply, connected with the included IEC cable. Leave space for airflow around the case.
2. Install Focusrite Control 2
Install Focusrite Control 2 on Windows or macOS before connecting the USB-C cable. On Windows, this also provides the ASIO driver. Then pair the iOS or Android app if you want to set preamp gain from the live room.
3. Choose the sample rate early
Pick 44.1 or 48 kHz for most sessions. That matters on this interface because ADAT carries 16 channels only at those rates. At 96 kHz the two ADAT ports carry up to eight channels. Set the same rate in your DAW and in Focusrite Control 2.
4. Set the buffer size
For tracking, start at 64 or 128 samples. If the computer crackles with many tracks armed, raise it one step. Then rely on direct monitoring through Focusrite Control 2 so performers hear themselves without delay. For mixing, use 512 samples or more.
5. Build headphone mixes
The two headphone outputs are independent. Create one mix for the engineer and one for the performer. Furthermore, you can send extra mixes to line outputs and feed an external headphone amp for a full band.
6. Use Auto Gain, then check by ear
Ask each player to perform at full intensity, then trigger Auto Gain. Afterwards, turn on Clip Safe for unpredictable sources like a shouting singer. Still listen to every channel, because a level that looks right can hide a bad mic position.
Talkback and speaker switching in a session
The built-in talkback mic lets you speak into the performers’ headphones without a spare microphone. Route it in Focusrite Control 2 to the cue mixes only, so it never reaches the recording. That simple step avoids voices on your takes.
Alt speaker switching lets you compare a mix on two monitor pairs. For instance, wire large monitors to one pair of outputs and small speakers to another. Switching quickly between them shows whether the bass and vocal balance holds up on both.
Scarlett 18i20 vs other multi-preamp interfaces
The table compares published figures for the 18i20 and three related interfaces.
| Spec | Scarlett 18i20 (4th Gen) | Clarett+ 8Pre | Clarett+ 4Pre | Scarlett 4i4 (4th Gen) |
|---|---|---|---|---|
| Mic preamps | 8 | 8 | 4 | 2 |
| Mic gain | 69 dB | 57 dB | 57 dB | 69 dB |
| Mic EIN | −127 dBu (A-wtd) | −129 dBu | −129 dBu | −127 dBu (A-wtd) |
| Line outputs | 10 | 10 | 4 | 4 |
| Line output dynamic range | 122 dB | 124 dB | 124 dB | 120 dB |
| Headphone outputs | 2 independent | 2 | 2 | 1 |
| ADAT | Dual in and out, up to 16 ch | 8 in, 8 out | 8 in | None |
| Auto Gain / Clip Safe | Yes | No | No | Yes |
| Talkback mic | Built in | No | No | No |
| Simultaneous I/O | 26 x 26 | 18 in / 20 out | 18 in / 8 out | 6 x 6 incl. loopback |
In short, the 18i20 offers more gain, automatic level tools and more digital I/O. The Clarett+ 8Pre answers with lower preamp noise, higher output headroom and analogue Air with impedance switching. Choose the 18i20 for convenience and channel count. Choose the 8Pre if analogue character and output specs matter more.
Pros and cons
Pros
- Eight preamps with 69 dB of gain each.
- Auto Gain and Clip Safe across all eight mic channels.
- 26 inputs and 26 outputs with dual ADAT, S/PDIF and MIDI.
- Two independent headphone outputs and a talkback mic.
- Remote control from a phone or tablet.
- Word clock for syncing with other digital gear.
Cons
- Needs mains power, so it is not a portable interface.
- Only two front-panel instrument inputs.
- Uses USB 2.0, so very large track counts depend on a stable computer.
- Preamp noise is slightly higher on paper than the Clarett+ range.
Common mistakes with the 18i20
- Choosing 96 kHz with full ADAT expansion. You lose half the ADAT channels. Decide the rate before wiring.
- Clock conflicts. When an ADAT preamp is connected, set one device as master and the other to follow. Clicks are the usual symptom of a conflict.
- Talkback on the recording. Route talkback only to cue mixes.
- Trusting Auto Gain blindly. A drummer often hits harder in the take than during the level check. Leave extra headroom on drums.
- Ignoring phase. With eight mics on a kit, check overheads against the snare and kick. Flip polarity in the DAW where the sound thins out.
- No labels. Name every DAW input to match the physical channel. It prevents confusion when the session gets busy.
Who should buy it and who should skip it
Buy the 18i20 if you record drums, bands or a rack of synths. It also fits engineers who want remote control and talkback. Skip it if you record one or two sources at a time, because a compact Scarlett 4i4 does that with bus power. Skip it as well if you need analogue colour on the way in more than automatic tools.
Expanding the 18i20 over ADAT
The eight built-in preamps cover a basic drum kit. A full band, however, often needs more. The dual ADAT inputs solve that. Connect one or two eight-channel ADAT preamps, and the 18i20 can record up to 24 mic channels at 44.1 or 48 kHz.
Wiring is simple. Run an optical cable from the preamp’s ADAT output to the 18i20’s ADAT input. Then decide the clock. Many engineers make the 18i20 the master and set the preamp to follow over ADAT. Others use word clock instead. Either works, as long as only one device leads.
The ADAT outputs are useful too. They can feed extra outputs on an expander for more headphone mixes or outboard sends. In Focusrite Control 2, those channels appear as normal outputs you can route like any other.
Planning a full band session
Before the band arrives, write an input list. It should name each source, the microphone and the input number. This step catches problems early, such as running out of phantom-powered channels or instrument inputs.
A typical plan uses the eight preamps for drums. Then the two instrument inputs take bass DI and a keyboard. Next, ADAT channels handle guitar amp mics and vocals. Finally, the line inputs capture a stereo synth or a drum machine.
Next, plan the headphone mixes. Drummers usually want more bass and click. Singers want more of their own voice and some reverb. With two independent headphone outputs plus line outputs feeding a headphone amp, everyone can get a usable mix.
Then do a quick test recording of a full song section. Listen back on monitors before the real takes. That pass often reveals a buzzing cable, a rattle on the kit, or a mic that moved.
Lastly, save the Focusrite Control 2 setup and the DAW template. The next session with the same band will then take minutes instead of an hour. Labelled cables help just as much.
Air modes and Harmonic Drive
Each preamp offers Air in two flavours. Presence adds a lift in the upper range for a clearer, more open sound. Presence and Harmonic Drive adds that lift plus gentle saturation. Both are optional, and both are recorded with the signal.
Use them with care. Presence can help a dull vocal or a dark acoustic guitar. Harmonic Drive can add weight to a bass DI or a room mic. On cymbals or bright condensers, however, leave Air off. You can always add brightness in the mix, but you cannot remove it from a recorded track.
FAQ
Does the Focusrite Scarlett 18i20 4th Gen have Auto Gain?
Yes. Auto Gain sets all eight mic preamps, and Clip Safe adjusts gain if a channel nears clipping.
How many ADAT channels does it support?
Two ADAT ports carry 16 channels at 44.1 or 48 kHz, and up to eight at 96 kHz.
Can it be controlled from a phone?
Yes. Focusrite Control 2 has iOS and Android apps that pair with the desktop app.
Is it rack mountable?
Yes. It is a 1U unit and ships with rack ears.
How many inputs does the 18i20 have?
Up to 26 inputs including ADAT, S/PDIF and loopback; 8 are mic preamps.
Can it record a full drum kit?
Yes, eight preamps cover a typical kit. See our drum recording mics guide.
Does it need a power adapter?
Yes.
New to choosing interfaces? Start with how to choose an audio interface and our Scarlett buying guide.