RME Babyface Pro FS: power output and what it will drive

The RME Babyface Pro FS is an audio interface at $899. It delivers 374 mW into 32Ω and 40 mW into 300Ω, which ranks it 123 of 280 for raw power among the sources in this database.

Measured at 100 dB SPL it has comfortable headroom on 550 of the 567 dynamic and planar headphones catalogued here, enough but not generous on 14, only marginal on 1 and not enough power for 2. The maker publishes a maximum output voltage but no power figure at any load, so every number here is an upper bound rather than a rating.

The manufacturer publishes a maximum output of 3.46 V but no power rating at any load. Every figure above is therefore a ceiling: the real output into a low impedance will be lower, possibly much lower.

Derivation holds output voltage steady between and beyond the published loads rather than output power, because that is what an amplifier actually does. The full method is written up here.

Source: rme-audio.de.

Ordered from easiest to hardest to drive. Headroom is measured at 100 dB SPL, which is louder than almost anyone listens — a small negative number means the source still plays loud, just without reserve for peaks.

These figures come from each manufacturer's own sensitivity rating. A handful of planars — the HiFiMAN Susvara and the Abyss AB-1266 in particular — are widely reported to need far more than their published sensitivity implies, so treat a bare pass on those as optimistic rather than settled.

At 6.3 µV of output noise, here is where that noise lands in the five most revealing in-ears in the database.

This one hisses. With the most sensitive in-ears in the database its own noise lands around 37 dB SPL, which you will hear between tracks and in quiet passages.

At 10Ω output impedance, the one-eighth rule says this source suits headphones of 80.0Ω and above. 510 of the 567 models here fall below that. That is most of the database, not a niche — 222 of them multi-driver in-ears, and the mismatch tilts the frequency response audibly rather than subtly.

The rule is a rule of thumb, not physics: a source impedance below one eighth of the headphone's keeps the interaction under about 1 dB. The checker works it out for any pair.

Of the 280 sources here, 40 do everything the RME Babyface Pro FS does as a headphone output: reach 100 dB on every headphone it reaches, stay inside the one-eighth rule wherever it does and stay under the audible-hiss threshold wherever it does. The cheapest of them is the FiiO KA11 at $29, against this one’s $899 — $870 less, and a USB dongle rather than an audio interface.

This counts a headphone output and nothing else. Inputs, converters, microphone preamps, balanced outputs, the volume control, the case and the warranty are all outside it, and any of them can be the reason to buy the dearer box. What the count does say is that the three numbers a maker can be held to do not separate them.

Worked out in advance against its closest rivals: vs Apogee Duet 3 · vs Audient EVO 16 · vs Audient iD44 MkII · vs RME ADI-2 DAC FS · vs RME ADI-2 Pro EX · vs RME ADI-2 Pro FS R · vs RME Fireface UCX II · vs RME Fireface UFX II · vs RME Fireface UFX III. Each of those pages lists the headphones that tell the two apart.

Or put any two side by side in the source comparison tool, or run your own headphones through the amplifier matcher. Or see every RME source in the database, and how much of what this site says about them came from RME’s own documents.