Both are audio interfaces, $899 against $1749. 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 RME Babyface Pro FS reaches 100 dB on 565 of the 567 models here, the RME Fireface UCX II on 564.
| Specification | RME Babyface Pro FS | RME Fireface UCX II |
|---|---|---|
| Power into 32Ω | 374 mW | 210 mW |
| Power into 150Ω | 80 mW | 45 mW |
| Power into 300Ω | 40 mW | 22 mW |
| Power into 600Ω | 20 mW | 11 mW |
| Output impedance | 10 Ω | 1 Ω |
| Output noise | 6.3 µV | not published |
| Price | $899 | $1749 |
| Headphones it reaches 100 dB on out of 567 | 565 | 564 |
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.
| Load | RME Babyface Pro FS | RME Fireface UCX II |
|---|---|---|
| 32 Ω | Upper bound | Published |
| 150 Ω | Upper bound | Derived |
| 300 Ω | Upper bound | Derived |
| 600 Ω | Upper bound | Derived |
These two columns are not the same kind of number, and that matters more than the gap between them. RME Fireface UCX II publishes a power rating (at 32 Ω); RME Babyface Pro FS publishes no power figure at any load, only a maximum output voltage, so every milliwatt in its column is a ceiling worked out from that voltage.
A ceiling assumes the amplifier holds that voltage into the load, and nothing on RME Babyface Pro FS’s own sheet says it does. It is the most flattering reading available, and it is used here only because the alternative is a blank. Where the RME Babyface Pro FS column looks the stronger of the two, treat the difference as unproven rather than measured. 24 of the 280 sources here are in that position, with no published power rating at any load.
What each of these labels means, and why a derived figure is still worth printing, is set out in how this data was built.
1 headphone reaches 100 dB on the RME Babyface Pro FS but not on the RME Fireface UCX II — Symphonium Crimson.
495 headphones are left alone by the RME Fireface UCX II under the one-eighth rule but coloured by the RME Babyface Pro FS (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Ocean, 492 more).
564 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.
The counts above say how many models the two treat differently. This says by how much. The same 8 headphones appear on every page of this kind, ordered from the easiest to drive to the hardest, so a row can be read across pages as well as across columns. Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Audio-Technica ATH-R70X: RME Babyface Pro FS has +12 dB of headroom there against +10 dB. 3 dB is about 1.8 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for RME Fireface UCX II because that maker publishes no output noise figure. That is a gap in the specification, not a quiet amplifier, and it is left blank here rather than filled with a plausible number.
| Headphone | Impedance | Needs | RME Babyface Pro FS headroom | RME Fireface UCX II headroom | RME Babyface Pro FS hiss | RME Fireface UCX II hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +34 dB damping | +32 dB | 30 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +14 dB damping | +12 dB | 10 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +23 dB damping | +21 dB | 9 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +19 dB | +16 dB | 4 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +16 dB damping | +13 dB | 3 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +12 dB | +10 dB | -3 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +8 dB | +5 dB | -7 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +6 dB damping | +3 dB | -9 dB | not published |
The RME Fireface UCX II costs $850 more than the RME Babyface Pro FS. Out of the 567 models here, that difference buys 495 more models left alone under the one-eighth rule.
It does not run one way only: the cheaper RME Babyface Pro FS drives one model to 100 dB that the RME Fireface UCX II does not, which is the part worth checking against your own headphones before paying the difference.
Everything in this paragraph counts only figures the two makers published. An advantage on an axis one of them leaves blank cannot be counted, and is not counted — how often that happens is its own page.
Each has a page of its own with every power figure traced to what the maker published and a full headphone list: RME Babyface Pro FS and RME Fireface UCX II. Or put either against your own headphones in the source comparison tool.