Motu 828es Phase Issues

[GianlucaDelfino]

I agree: if MOTU could clarify this, it would be best.
However, I do not think this is going to happen anytime soon.

If you wonder what is the phase relationship of the various channel, from my tests I can say that there is a difference between front inputs (with preamplifier) and rear inputs. odd pairs at the back are perfectly in phase as well as even pairs. Each rear odd input show a one-sample delay compared to the any of the even channels.

The behavior of front inputs is mirrored: channel 2 shows a one-sample delay if compared to channel 1

[HCMarkus]

it might be interesting to see if this issue is common with a particular chipset or across different manufacturers' interfaces.

This.

[GianlucaDelfino]

I can tell you I tested:

Focusrite Saffire dsp 24
Soundcraft mtk 22
Soundcraft mtk 12
Behringer umc1820

And none of them showed phase alignment problems

[Phil O]

Dear Phil, thank you for your reply.

As stated earlier, I am not concerned with microphone placement.

Whether the problem is relevant or not, is a matter of what you use the interface for.

I am just trying to understand whether this is a fault in my unit or a design flaw.

Sorry, I didn't mean to come across as judgmental. But I am curious as to what your application is.
As far as your particular unit vs design flaw vs limitation of the converters used, my vote would be converter limitations. But of course I'm speculating. MOTU tech support is usually pretty good about issues like this, but sometimes a little nudge helps. I would ask if they were able to duplicate the problem.

Your friendly neighborhood Phil

[bayswater]

FWIW I tried to replicate on the Focusrite Scarlett 18i8 Gen 1, and DP, but all is tickety-boo.

[GianlucaDelfino]

Thank you Phil,

Don’t worry, your post was not judgmental in any way.

I am using my MOTU to record a mixdown of live sessions of electronic music performed on an allen&heath gl2800. I am recording the master LR output and four stereo subgroups as stems. The phase alignment of the master LR is important to avoid frequency misrepresentation of mono components, but the phase alignment of all inputs is fundamental when I try to mix (in my daw) the stems and the master. I started perceiving a slight comb filtering effect when I was mixing a drum track stem to the main LR, so I started checking all my signal flow and analyzing all the stages and the misalignment happens at the MOTU stage.

I am just trying to keep the discussion on track: I need people to test their MOTU 828es to understand what’s the problem.
I know there are workarounds and I have found one myself, but I want to know if this is a design flaw and why MOTU haven’t managed to give me any clue in more than four months. As a consequence, I may decide I should sell my 828es to someone who thinks this issue is not relevant and buy an RME.

It’s easy and should not take long: just feed the exact same signal to inputs 1&2 and check with MOTU Audio Tools phase analyzer (rectangular) whether it tilts or not (you may need to magnify x-axis resolution by a sensible amount).

As for the little nudge to MOTU support, I have been writing constantly, every 15 days since September 2023, with no result. My ticket is still open, but I was told not to expect any update soon. If you are interested in the issue, you may open a ticket yourself, I would really appreciate, thank you.

[EMRR]

I agree I would not feel great printing an analog mix back with this problem.

When i transfer cassette tapes with a phase meter open, I see that curve in the highs swimming around as tape alignment changes, looks like something pushed by a breeze. Audible too, though probably because it’s actively changing.

[HCMarkus]

I agree I would not feel great printing an analog mix back with this problem.

When i transfer cassette tapes with a phase meter open, I see that curve in the highs swimming around as tape alignment changes, looks like something pushed by a breeze. Audible too, though probably because it’s actively changing.

Assuming you are talking about a stereo mix, you may wish to consider using a pair of Even or Odd inputs, as our OP's research suggests..