Short answer
Both are audio interfaces, $570 against $589.
The Universal Audio Volt 476P reaches 100 dB on 558 of the 567 models here, the Focusrite Scarlett 18i16 (4th Gen) on 553.
| Specification | Focusrite Scarlett 18i16 (4th Gen) | Universal Audio Volt 476P |
|---|---|---|
| Power into 32Ω | 55 mW | 84 mW |
| Power into 150Ω | 27 mW | 28 mW |
| Power into 300Ω | 27 mW | 22 mW |
| Power into 600Ω | 14 mW | 12 mW |
| Output impedance | 11 Ω | not published |
| Output noise | not published | not published |
| Price | $570 | $589 |
| Headphones it reaches 100 dB on out of 567 | 553 | 558 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | Focusrite Scarlett 18i16 (4th Gen) | Universal Audio Volt 476P |
|---|---|---|
| 32 Ω | Derived | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Published |
Both makers publish a power rating. Focusrite Scarlett 18i16 (4th Gen) publishes at 300 Ω; Universal Audio Volt 476P at 32 Ω, at 300 Ω and at 600 Ω. The other rows are worked out from those.
So the two columns are not equally firm row by row: at 32 Ω and at 600 Ω only the Universal Audio Volt 476P figure is the maker’s own. On those rows the derived number is the one to doubt first.
5 headphones reach 100 dB on the Universal Audio Volt 476P but not on the Focusrite Scarlett 18i16 (4th Gen) — HiFiMAN HE-6se V2, HiFiMAN HE6 Remastered, HiFiMAN Susvara, 2 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 HiFiMAN HE400se: Universal Audio Volt 476P has +9 dB of headroom there against +7 dB. 2 dB is about 1.5 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Focusrite Scarlett 18i16 (4th Gen) and Universal Audio Volt 476P because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Focusrite Scarlett 18i16 (4th Gen) headroom | Universal Audio Volt 476P headroom | Focusrite Scarlett 18i16 (4th Gen) hiss | Universal Audio Volt 476P hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +26 dB damping | +28 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +6 dB damping | +8 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +16 dB damping | +18 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +16 dB | +16 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +7 dB damping | +9 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +10 dB | +10 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +6 dB | +5 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | -1 dB damping | +0 dB | not published | not published |
The Universal Audio Volt 476P costs $19 more than the Focusrite Scarlett 18i16 (4th Gen). Out of the 567 models here, that difference buys 5 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: Focusrite Scarlett 18i16 (4th Gen) and Universal Audio Volt 476P.