Short answer
Both are audio interfaces, $720 against $699.
The Audient NERO reaches 100 dB on 559 of the 567 models here, the Focusrite Scarlett 18i20 4th gen on 553.
| Specification | Audient NERO | Focusrite Scarlett 18i20 4th gen |
|---|---|---|
| Power into 32Ω | 86 mW | 55 mW |
| Power into 150Ω | 23 mW | 27 mW |
| Power into 300Ω | 13 mW | 27 mW |
| Power into 600Ω | 7.4 mW | 14 mW |
| Output impedance | not published | 11 Ω |
| Output noise | not published | not published |
| Price | $720 | $699 |
| Headphones it reaches 100 dB on out of 567 | 559 | 553 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | Audient NERO | Focusrite Scarlett 18i20 4th gen |
|---|---|---|
| 32 Ω | Derived | Derived |
| 150 Ω | Derived | Derived |
| 300 Ω | Derived | Published |
| 600 Ω | Published | Derived |
Both makers publish a power rating. Audient NERO publishes at 600 Ω; Focusrite Scarlett 18i20 4th gen at 300 Ω. The other rows are worked out from those.
So the two columns are not equally firm row by row: at 600 Ω only the Audient NERO figure is the maker’s own and at 300 Ω only the Focusrite Scarlett 18i20 4th gen figure is the maker’s own. On those rows the derived number is the one to doubt first.
6 headphones reach 100 dB on the Audient NERO but not on the Focusrite Scarlett 18i20 4th gen — HiFiMAN HE-6se V2, HiFiMAN HE6 Remastered, HiFiMAN Susvara, 3 more.
553 of the 567 models here reach 100 dB on both.
Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Sennheiser HD 600: Focusrite Scarlett 18i20 4th gen has +6 dB of headroom there against +3 dB. 3 dB is about 2.1 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Audient NERO and Focusrite Scarlett 18i20 4th gen because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Audient NERO headroom | Focusrite Scarlett 18i20 4th gen headroom | Audient NERO hiss | Focusrite Scarlett 18i20 4th gen hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +28 dB | +26 dB damping | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +8 dB | +6 dB damping | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +18 dB | +16 dB damping | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +14 dB | +16 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +10 dB | +7 dB damping | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +7 dB | +10 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +3 dB | +6 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +0 dB | -1 dB damping | not published | not published |
The Audient NERO costs $21 more than the Focusrite Scarlett 18i20 4th gen. Out of the 567 models here, that difference buys 6 more models driven to 100 dB.
Nothing runs the other way: there is no axis here on which the cheaper of the two does better.
Only published figures count here; blank axes are counted separately.
Each in full: Audient NERO and Focusrite Scarlett 18i20 4th gen.