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MOTU M4 Loopback Measurements

isabido

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I do see your point now, sorry I didn't got it in the first place. It's kinda big roll-off @20Hz, maybe I'll give it a try to mine and check if it has the same behaviour too.
Hi TRL, were you able to check? I bought the card on Amazon and I could request a refund, but I doubt it is a specific problem with my card.

Occurring on both input channels equally, I'm pretty sure it's a design "fault".

Thanks in advance.
 
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L0rdGwyn

L0rdGwyn

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At some point I will try to check on my unit. I am suspecting it is a real problem, it would explain why I was seeing such significant bass rolloff when I was measuring an RIAA, rolloff that clearly was not audible and my math was correct on the filter...
 

trl

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Hi TRL, were you able to check? I bought the card on Amazon and I could request a refund, but I doubt it is a specific problem with my card.

Occurring on both input channels equally, I'm pretty sure it's a design "fault".

Thanks in advance.
I'm sorry mate, haven't got time yet, but I promise you that next week I will be on top of it. Thanks for understanding!
 

isabido

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Hi @trl I have taken the measurements again and the same results.

Here you can see very clearly. The output is always OUTPUT3 with the same cable.

It is rare for a card of this "level" to have such a noticeable flaw.

@amirm can this be? I am doing something wrong? I have doubts if it is a problem of impendances in the front inputs. channels 1-2.

Thanks in advance!



1651425159981.png
 

trl

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Hello,

Unless I did something wrong, I see only 0.3 dB @ 20 Hz and 0.8 dB @ 10 Hz difference between Input #3 and Input #1.

MOTU_M4_20Hz.png


MOTU_M4_10Hz.png


Inputs # 3 & 4 are probably direct coupled, while Inputs # 1 & 2 are most likely capacitors coupled.

I don't think there's something wrong with M4, but feel free to share your measurements details, in case I need to reproduce them exactly.

Thanks!
 

isabido

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Gracias @tlr, por tomarse la molestia de hacer las pruebas. En mi caso las diferencias son mas notables, no se que versión de hardware tendrá tu MOTU M4.

Creo que no es una buena respuesta la que ofrece mi MOTU M4 en mis canales de entrada 1-2. Mi viejo EMU-0404 USB tiene mejor respuesta que este.

1651438278244.png


1651438306796.png

To make this comparison easier, to take the measurements it is ideal to do it from PREFERENCES ---> Calibrate soundcar.

It directly returns the value to -3b.


1651438742087.png
 
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isabido

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HI @trl,

Here I leave the measurement of my old EMU-0404 USB. Much better than this new MOTU 04.

I want to assume that my MOTU 04 unit has no problem, and it is a design flaw in this latest hardware revision.

1651509871250.png


1651510305308.png
 

isabido

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Please, I would need some colleague who has the most recent hardware version purchased recently, to perform a loopback measurement between output 3 and input 1. I would like to rule out that my own card had any problem in order to make a return.

If you need help to perform this test I will be happy to help.

Let's see if together we can find out if Motu has made any design errors in these latest hardware changes. Thank you
 

isabido

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The puzzle is now solved!

The INPUT 1 jack must be a high-impedance instrument-only input, I was using a JACK-JACK cable.

I've tried using the XLR connector, and now you do get a decent response. Not as good as INPUT 3, but it makes sense!

Be careful using INPUT 1 XLR, as line input, because if we press phantom power we can cause a problem.


1651961003259.png
 

isabido

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Hi guys, new M4 owners could you please do a loopback test with TRS cable? (output 3 and input 1) Thanks!
 

137tmxth

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I finally ran this test on my unit which is either a rev2 or rev3, probably rev2. I'd open it check which chips it's actually using right now, but I don't have the correct bit for those hexagon head screws without buying one first.

Seems I have the exact same problem as @isabido, and I did notice earlier that the sound wasn't quite right when I tried to capture audio from an old MIDI synth module using the front inputs, but I thought the culprit might have just been my cables or RCA->TRS adapters.

m4_results.png

Now what to do about it? Even if I could get Thomann or MOTU to acknowledge there's a problem and agree to a swap I don't really want to go to rev1. I wonder, does rev3 fix it, assuming my unit is a rev2? Is there a rev4 yet?

I don't think using XLR cables for line sources is a proper solution. The manual specifically tells to NOT do it, and the signal will be degraded slightly because it goes through additional unnecessary preamps. Accidentally activating phantom power while there's a line device connected via XLR to the front inputs is also a real possibility...

The unit is quite nice otherwise and thankfully I don't really ever need four line inputs active at the same time, but the gain adjustments available only on inputs 1-2 could be really useful sometimes because I have much "consumer" grade gear which output relatively quiet "line" signals, and sometimes I'd like to monitor the signal from them at a reasonable level without going through the host computer to apply gain in software.

Has anyone contacted MOTU support about this yet? I might try and see what they say. The unit is supposed to have 4 fully usable line inputs, it was always marketed as such, and we know the first hardware revision did not really have this problem.
 

isabido

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Thanks for sharing your results, indeed you have exactly the same answer in frequency in each of your two tests.

If you review the tests carried out by @amirm, at no time does it test IN1/IN2, it only does so with the TRS connections. So the only real proof that rev1 is not affected is the action taken by @trl
 
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