I did some more testing on this using the Bit Test.

Using iTunes as playback software and QuickTime Player as recording software, the recorded signal from the DAC is bit perfect up to 24/192 regardless of Source being Optical or USB (Rec. opt.).

The signal flow between playback and recording software is as in the original post.

For playback, iTunes was set to full volume (slider all the way to the right) and all enhancements were disabled or set such that the signal is not altered by iTunes. For recording, on the QuickTime Player, the DAC was set as the microphone and the quality was set to maximum. The sample rate and word length (number of bits) for the SPDIF output and the sample rate of the DAC were set in the Audio MIDI Setup's Audio Devices such that the word length and sample rate were those of the bit test file being played back.

Playing back the 32 bit tests using USB, shows that iTunes truncates at 24 bits as the test passes for all sample rates but only at 24 bit. Using the tests at 16 and 24 bits and also using SPDIF, as it is limited to 24 bits, the test passes for both 16 bits and 24 bits for all sample rates for both SPDIF and USB, i.e. the signal from iTunes to the DAC is bit perfect for both USB and SPDIF up to 24/192.

Thus, the signal being sent to the DAC is bit perfect up to 24/192.

The bit perfect transmission from the DAC was tested by recording the incoming bit test (and bit perfect) signal and subsequently playing the recorded signal back in iTunes. This was done both for Source being Optical and Source being USB (Rec. opt.). All the recorded bit test signals resulted in the same pass as the original bit test signals regardless of Source being Optical or USB (Rec. opt.).

Thus, the recorded signal from the DAC is bit perfect up to 24/192 regardless of Source being Optical or USB (Rec. opt.).

Thanks, that made it work. Although I am not sure why the support didn't manage to provide that via mail.

Now, about my second post. The manual says on page 10

My testing suggest that this is not the case. Rather, it seems that the DAC records any SPDIF signal present at the selected playback/recording input and transmits it via USB if connected.

Even if the USB sample rate is the same as the SPDIF sample rate?

Habe ein ähnliches Problem: Digicheck zeigt nichts an. Digicheck darf Mikrofon benutzen. Macos Mojave.

Gibt es Vorschläge?
Danke

I made the error to have MATLAB not read the files in their native format but rather in its standard 64 bit double precision float. The recordings are 32 bit integer files while the 24 bit test file is 32 bit integer but the 16 bit test file actually is 16 bit integer. After correcting for the above, the comparison can thus only be made with the 24 bit test.

However, this returns the same result as before: No errors using both Optical and USB (Rec. opt.) for recording.