Topic: Distortion problem one channel at 192 kHz
I have a MADI HDSPe card with the latest driver 4.38 and two ADI-642 MADI to AES peripherals. A third 642 spare is available and I've used it for debugging. I so rarely work at 192 kHz, but I have not been able to work at 192k for a very long time. Using an external ADC/DAC converter pair I send audio out 2 channels of a 642 to a DAC for analog processing and then back to the ADC which returns on two channels of a 642.
Things work fine at 96 kHz. The problem at 192k is sometimes distortion on the right channel, or considerable white noise measuring around -56 dBFS on the digicheck meters in both channels. Clearly that is that white noise that I hear. I always see the noise on the ADC return at around -56 dBFS in Sequoia. Strangely, the noise is visible but it is inaudible if I route it to my monitor DAC. However, if I route the ADC return to an RME loopback, and then to the monitors, then I can hear the white noise quite obviously.
Measurements correspond with the noise issue. The ADC return measures around -110 dBFS in Digicheck's bit statistic and noise meter and this is inaudible. But as I said, the ADC return shows around -56 dBFS on both channels in Sequoia. Only if I route the ADC out to an RME loopback channel and then return it -- then I can hear and see the noise and Digicheck measures around -56 dBFS on the loopback return, 20-20 khz. Again, all of this goes away at 96 kHz sampling.
Wordclock is generated by the ADC on internal sync, goes to the MADI card and then the MADI card feeds WC to the 642s, which are all locked to word clock. Of course I am using 48k frame. The problem does not go away if I lock the 642's to MADI instead of WC.
I need to isolate this problem. Could it be the HDSP card (SMUX problem?). It can't be one of the 642s as I have a spare 642 and replaced one of them so far and the problem persists. I am wiling to buy another MADi card and test it if you think it might be the card.