zamproject
Well-known member
- Joined
- May 11, 2010
- Messages
- 1,512
Hello
I just purchase a motu PCIe card to update my motu PCI ring (24io), in short I have to replace my G5 which start to have some problem with a mac pro (on his way)
I have a good trade for a 2408mk3 coming with the PCIe card so I take it too
Now the point:
I hook up everything to my analogue setup (28 chn desk), and decide to compare 24io to 2408 when printing my mix master 2T
I split at patchbay and send master out to 2in at both converter.
Then I compare difference in audio files at daw with phase flip for on, instantly It was wrong !!! cancellation was a disaster (files are sample accurate...). Quick A-B test don't reveal drastic difference as the phase cancellation test might suppose ...
So I perform loop back directly for both converter, phase cancellation is excellent from source (by tweaking 0.01 or 0.02 dB) for each converter.
Then I perform two loopback 24io to 24io and 24io(same out as before, same cable) to 2408 and then I test by phase cancellation... disaster !!! for this last test I use 5Hz-20kHz 30 sec sweep and I notice the result of phase cancellation test is a perfect cancellation at low freq and NO cancellation at 20kHz. The cancellation "error" is linear (in log freq scale)
My conclusion is that one of the two converter continuously shift the phase from 0° to 180° in the 20Hz/20kHz freq range.
Is that due to how the AD chips and digital filter is handled ?
I just try to search and have some read about this, but I'm not expert in digital signal...
Can this be relater to the fact that one ADC have 128x oversampling and the other 64x
Any input and science (basics) welcome
Best
Zam
I just purchase a motu PCIe card to update my motu PCI ring (24io), in short I have to replace my G5 which start to have some problem with a mac pro (on his way)
I have a good trade for a 2408mk3 coming with the PCIe card so I take it too
Now the point:
I hook up everything to my analogue setup (28 chn desk), and decide to compare 24io to 2408 when printing my mix master 2T
I split at patchbay and send master out to 2in at both converter.
Then I compare difference in audio files at daw with phase flip for on, instantly It was wrong !!! cancellation was a disaster (files are sample accurate...). Quick A-B test don't reveal drastic difference as the phase cancellation test might suppose ...
So I perform loop back directly for both converter, phase cancellation is excellent from source (by tweaking 0.01 or 0.02 dB) for each converter.
Then I perform two loopback 24io to 24io and 24io(same out as before, same cable) to 2408 and then I test by phase cancellation... disaster !!! for this last test I use 5Hz-20kHz 30 sec sweep and I notice the result of phase cancellation test is a perfect cancellation at low freq and NO cancellation at 20kHz. The cancellation "error" is linear (in log freq scale)
My conclusion is that one of the two converter continuously shift the phase from 0° to 180° in the 20Hz/20kHz freq range.
Is that due to how the AD chips and digital filter is handled ?
I just try to search and have some read about this, but I'm not expert in digital signal...
Can this be relater to the fact that one ADC have 128x oversampling and the other 64x
Any input and science (basics) welcome
Best
Zam