Both are audio interfaces, $279 against $279. This page puts them side by side on the only three things a maker can be held to — power, output impedance and noise — and then asks the question that actually matters: which headphones do they treat differently?
The MOTU M4 reaches 100 dB on 565 of the 567 models here, the Focusrite Scarlett 4i4 4th gen on 553.
| Specification | Focusrite Scarlett 4i4 4th gen | MOTU M4 |
|---|---|---|
| Power into 32Ω | 55 mW | 333 mW |
| Power into 150Ω | 27 mW | 71 mW |
| Power into 300Ω | 27 mW | 36 mW |
| Power into 600Ω | 14 mW | 18 mW |
| Output impedance | 11 Ω | not published |
| Output noise | not published | not published |
| Price | $279 | $279 |
| Headphones it reaches 100 dB on out of 567 | 553 | 565 |
A figure marked not published is missing from the maker’s own material, which is not the same as being good or bad. Where one of these two publishes a number and the other does not, the comparison on that axis cannot be made at all — and saying so is more useful than guessing.
12 headphones reach 100 dB on the MOTU M4 but not on the Focusrite Scarlett 4i4 4th gen — HiFiMAN HE-6se V2, HiFiMAN HE6 Remastered, HiFiMAN Susvara, 9 more.
553 of the 567 models here reach 100 dB on both. That is a power count and nothing more; whether either source suits a given headphone also depends on the two lines above.
Each has a page of its own with every power figure traced to what the maker published and a full headphone list: Focusrite Scarlett 4i4 4th gen and MOTU M4. Or put either against your own headphones in the source comparison tool.