Just for me to understand as I have never used a RME unit. You mention an ADC, is that a separate box or the ADC in the RME? Is the SPDIF loop-back internal in the RME or did you connect SPDIF out to in, by cable on the RME. Or was the loop-back done in a separate box? If so, what was that?
I understand that SPDIF and AES are in principle the same save for the voltage level and one "control bit". The signal fed to the Okto was that SPDIF or AES and if SPDIF from the RME was is the same signal as the loop-back?
The RME is an interface with lots of analog and digital I/O, see here for more info -> https://archiv.rme-audio.de/en/products/fireface_800.php. A rough sketch of the hardware setup is shown below.
In this case I have the RME mixer set so that when I play to channel 1/2 it outputs to both the optical and coaxial SPDIF outputs. RME coaxial SPDIF output is AES compatible and is connected to the Okto via a coaxial to XLR cable to AES input 1-2. RME optical SPDIF output is routed to the RME optical input for use as a timing reference. Okto analog output 1 is routed to RME analog input 1 for use as the main measurement channel. In REW the left channel is used as the main measurement channel and the right channel is used as the timing reference.
Sorry for all the questions but since I'm mixing two different DAC's in the same system understanding why I got +2ms and you got 1,23ms is important in my system. I need to delay my other DAC's to compensate for the Okto latecy. And gain.
Important to note that the setup describe above was an attempt to quantify worst case absolute latency of the Okto. If I wanted to use the Okto in a system in conjunction with the RME analog output and wanted to determine relative latency between the Okto and RME analog outputs, I would have used the analog output of the RME as a timing reference, not the SPDIF output.
Can you please check levels also, ie what is the level out, at 100% volume, compared to input. Just a compare measure would be great. My finding of +5db sounds high.
I get 4.3 V from the Okto when fed a 0 dBFS sine at 100% volume.
A few questions for you. From your description you are sending an analog signal to the BSS, what specific hardware are you using to do this? I assume that this device also has an ADC that you are using for measurements? I assume your measurements are electrical, not acoustic via a microphone? What specific BSS DSP are you using?
Michael