Reported by Anonymous

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The U7 is an external USB 2.0 sound card according to UAC-2 standard. It has a stereo analog input, a stereo headphone output, a digital (SPDIF) output, 24 bit, analog 7.1 cinch outputs with 690 Ω output impedance. The AD converter is a CS5361 with 192 kHz. The headphone output has an output impedance of 21 Ω and is only recommended up to an impedance of 200 Ω, not quite a quality label. The operational amplifiers are by no means a bad choice, LME49726 from TI are built in, which can produce an impressive 300 mA output current, and the noise density is typically 8.3 nV / √Hz. The -3 dB bandwidth on both the headphones and the cinch output is measured at 53 kHz, at 90 kHz the level is -18 dB. The combined microphone / line input is often criticized and is often the cause of problems. thumbs down. A volume control for the output level is a very user-friendly feature, so you don't have to bother with the mouse or the "up" and "down" keys but can set the volume very intuitively and quickly. Under Windows 10, the microphone input shows an impedance of 4 kΩ and a full scale at approx. 0.9 V s . The line input has full modulation at 2.82 V s and an impedance of 50.0 kΩ. Behavior is somewhat different under Linux with ALSA (UAC-2). The line input behaves the same as under Windows, but the microphone input has the same modulation limit and sensitivity as the line input. The input impedance is 50.06 kΩ at 1 kHz. Switching to 'Mic' switches a DC supply voltage of approx. 2.5 V to the inputs. The input level is reduced by 0.3 dB. The distortions at full level increase in Mic mode. The U7 does not have a physical microphone amplifier, the windows driver does just a software amplification, which greatly reduces the s/n ratio. If you want to use microphone, don't buy the U7. With subsonic signals, the distortion increases below 20 Hz, with a serious peak at 5 Hz, very strange, but you must avoid signals below 10 Hz with the U7. The sampling bandwidth under Linux and ALSA corresponds to the expectations for 192 kHz sampling rate. The inherent noise looks like the application of noise shaping, which is well done. Here with 50 Ω at the line input and with an open input. The mirror frequencies are safely kept out of the listening area. The plastic housing is shabby: a hum is clearly visible in the spectrum, which disappears completely if you simply wrap the device in aluminum foil.
If you don't need the microphone input and headphone output, you still have a good sound card with high resolution and very low noise.

Reported by Dan

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Tried Asus Xonar U7 MKII on Linux Mint 20 Ulyana.
It works out of the box without installing anything (only stereo output tested).
There is no noise, sound quality seems good, no distortions. One might think the limit is the quality of the recording.
However, when comparing same music and same hardware configuration, but under Windows 10, there is a significant difference:
Under Windows 10:
- sound is much louder
- there are more details (sound quality is great under Windows; love it)
I believe the Linux driver lowers the bit depth before rendering.

On my current system I have Xonar U7 MKII connected to dedicated amplifier with speakers and HDMI monitor with speakers.
When comparing under Linux, the Xonar + dedicated speakers seems to me to have less details than HDMI monitor speakers (however, much lower distortions)

Also, the buttons and the volume knob on the sound card don't work under Linux, but that's not the problem. (reduced 1.5 stars for the sound quality, nothing for this)