RME ADI-2 DAC Bit-perfect test files wrong bit depth?

Question to anyone with an RME ADI-2 DAC (firmware V.24).
When playing the RME bit perfect test files through roon I am getting a possibly odd behavior.
Regardless of the sample rate the results on the ADI-2 DAC show ‘Bit test 24 bit passed’ with the 16 bit files, ‘Bit test 32 bit passed’ with the 24 bit file and nothing with the 32 bit file. Same results for 44.1, 96k and 192k sample rates.

If anyone with an RME ADI-2 DAC can check and confirm similar behavior I would be interested.

This is when playing via USB directly from ROCK or from Pi3b+ running Roonbridge.

Not sure if this is a roon issue or if it is the latest (V.24) firmware. All the files showed bit perfect last time I checked, but that was older firmware from LMS to a picoreplayer USB to the RMI.

Zero padding, most likely. For example, 16 bit signals are being padded with zeros that occupy the eight LSBs to form 24 bit samples. Technically, the binary values have not changed – just as decimal values can be zero padded to the left (5 = 0005).

Some DACs detect zero padding, disregard the padded zeros in the physical bit depth, and report only the logical bit depth. Other DACs count the padded zeros as part of the logical bit depth.


Response from the RME forum. It is an issue with latest firmware and will be fixed.
The DAC firmware 26/24 shifts the display of the bit test result by one: 16 Bit is shown as 24 Bit, 24 as 32, and 32 not at all.

Roon and the RME-ADI-2 DAC are both behaving correctly.