It's an old Fireface 400. Specs show AD/DA, -1 dB: 1 Hz - 80 kHz (sf 192 kHz).
And the headphone output even goes to zero Hz. Yes, you can generate a DC voltage up to 5V reliably. Higher too, but not as precise. I've used that to generate PWM square waves.
I've done the same with a Fireface 800 and 802. These interfaces come with a measurement software, called Digicheck. Oscilloscope, vector scope, frequency analyzer and a few other useful utilities, like a digital quality display.
All current RME's interfaces go up to that frequency. And even most of the older ones. And I think the Apogee, Lynx and others do too, but I've never measured those. Sometimes, the mic preamps don't because of RFI protection. Line inputs will be more linear. But the RME QuadMic, fi has a spec at -0,5 dB: 5 Hz - 200 kHz... No AD/DA, purely analog. That's in case you have an external 384 kHz sample rate converter.
The ADI-2 seems limited because it's a spec -1 +1 dB I think. It reaches 95 kHz, but with around -3 dB or so. RME is very precise with its specs...
They're German...
I have used these to record bats, rats and mice.
The biologists I was helping then later bought an italian ultrasonic USB mic because it was cheaper and handier. But that didn't exist when I got the FF400.
If you want uber performance, there's another German manufacturer that has a true 32 bit interface that goes up to 384 kHz. Starting at 12.000 € or so. I'd like to get my hands on one of those...
