Don‘t worry, I‘ve used a variety of USB cables with ADI-2, all generic and nothing fancy, without any problem.
Even some 15 m active ones worked well.
ADI-2‘s not picky, only it should be USB 2.
If you want to check, repeatedly run ADI-2 Bit Test (manual page 67).
It‘s very simple, it’s just playing certain files downloadable from RME.
From the DAC manual page 67:
31.14 Bit Test
A bit test is used to check the playback path for unwanted changes in the playback data. Playback software can cut bits, add dither, or change the level - without these changes becoming noticed easily. A poorly programmed driver can manipulate bits, and a playback hardware could be both badly designed and defective (hanging bits, swapped bits). Even such features as proper channel assignment, left/right synchronicity and polarity can be tested by a well-made bit test.
With a bit test, such errors can be detected and - more importantly - excluded.
How does it work?
Most bit tests take some time and are loud and unpleasant when playing through headphones or speakers. RME uses a unique bit pattern, with defined levels and pauses. This consists of only 400 samples (<10 ms), and sounds like a dull, medium-loud click - harmless for ears and equipment. The short, but efficient test sequence allows to check for the following changes and errors:
Level changes, equalization, dynamic processing, polarity, channel swapping, sample offset, hanging or twisted bits, dither, bit reduction.
The signal reaches the ADI-2 DAC via USB, AES or SPDIF/ADAT. The unit has three continuously running check circuits. If the test signal is detected correctly, the device's display shows a message: Bit Test 16 bits, 24 bits or 32 bits passed, depending on the detected signal. If the transmission path is not bit-transparent or bit-accurate, the signal only minimally changed, the message is not shown, the bit test failed. There is no error notice.
RME provides several audio files as free download: 44.1, 96 and 192 kHz in 16 bit, 24 bit and 32 bit. These files in WAV format can be played easily on Windows, Mac OS X and Linux. For ease of use (looping, players with fade in/out), the files contain the bit pattern several times. Runtime is about 4 seconds.
The Zip archive contains:
441_16_adi2pro_bittest.wav 441_24_adi2pro_bittest.wav 441_32_adi2pro_bittest.wav
192_16_adi2pro_bittest.wav 192_24_adi2pro_bittest.wav 192_32_adi2pro_bittest.wav
Theoretically, the use of the 32 bit file is sufficient. If the lower bits on the transmission path are simply truncated, the corresponding message appears with the respectively recognized bit resolution, i.e. 24 or 16 bits.
iOS, AES, SPDIF and ADAT are limited to 24 bit.
Some players in Mac OS X offer a Direct Mode, using 32 bit integer in non-mixable format.
The 32 bit test might still fail. HQPlayer 3.20 and up is known to pass.
SPDIF/ADAT (AES) are checked behind clocking. Therefore the unit needs to be synchronized correctly to the digital input signal.