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MOTU M2 loopback measurements

boXem

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I bought the M2 for some debug and EOL testing.
Amongst the "cheap" interfaces, it was the one that seemed to have the lowest noise. I didn't really care about distortion since for accurate work, I plan to use an harmonic cancellation software.
So, here we go:
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And finally, for the IMD hump fetishists
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Edit: new set of measurements with much better noise figures on post #20
 
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lc155

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From what I can see (I'm not too huge into reading these charts, so inexperienced), there appears to be some IMD hump, but it is really quite minor compared to the usual cases we've seen on ASR, correct? Fairly interesting given how the older chips are supposed to be fine at least from what I've read on the subject.
 

lc155

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Well, since it's loopback, the ADC accuracy plays a large role. So it's difficult to draw conclusions on the significance of the hump. We can see it, it's all we can say.

Fair enough. It's a little disappointing but then again I have never heard of a conclusive 'is this actually audible' argument here before, just the debate that it is annoying that they've regressed in quality.
 

MNMLSM

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Thanks for the input. Unfortunately those diagrams give me zero information, is there a link which explains the meaning? :)
I'd really like to get a MOTU, I read that the M4 is pretty impressive for it's price tag but I don't need the extra ports. Does The M2 also perform that great? I'm currently using the Behringer Q502 USB with my Mackie MR524 and I get a decent buzzing the whole time also I would like to get an aesthetically more pleasing unit.
Would you recommend the M2 in that price range? I would use it for my Mackies and the AKG K712 Pro a mic is in the planning.
Thanks guys!
 

Blumlein 88

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So pretty much noise limited on Sinad to around -87 db or so. Very low distortion.

What size FFT are you using?
 

lc155

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Yes, I am a bit disappointed by the noise level.

FFT 1M with 32 averages.

While that appears fairly bad with my rudimentary understanding, is it audible in practice? I presume SINAD isn't related to EIN, as this thing has been praised for extremely clean mic pres with low noise by those in the recording industry; enough gain and low noise enough to run dynamic mics like an SM7B without an external gain amp.

At this price point for a device that works as a 3-in-1, doing all three things (mic pre, monitor out, headphone out) extremely well, I don't know if you could ask for much more.
 
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boXem

boXem

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While that appears fairly bad with my rudimentary understanding, is it audible in practice? I presume SINAD isn't related to EIN, as this thing has been praised for extremely clean mic pres with low noise by those in the recording industry; enough gain and low noise enough to run dynamic mics like an SM7B without an external gain amp.

At this price point for a device that works as a 3-in-1, doing all three things (mic pre, monitor out, headphone out) extremely well, I don't know if you could ask for much more.
I didn't measure ADC noise by itself, so we don't know the noise source, could be the DAC.
When I am writing that I am disappointed, it's only because I will personally use it as an instrument for electronics testing. Not a judgement on intrinsic value as a sound card for musicians.

Now, as a normal user: looks cool, vu meter are cool too, even if quite slow, knobs are quite inaccurate.
 

Blumlein 88

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Just a question. On the TRS inputs, you have selected Line In, and not Guitar/Instrument? They both use the same plug. You'd get higher noise on guitar/instrument because it is 1 megohm input impedance.
 

Blumlein 88

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I didn't measure ADC noise by itself, so we don't know the noise source, could be the DAC.
When I am writing that I am disappointed, it's only because I will personally use it as an instrument for electronics testing. Not a judgement on intrinsic value as a sound card for musicians.

Now, as a normal user: looks cool, vu meter are cool too, even if quite slow, knobs are quite inaccurate.
A good way to measure ADC noise is to connect a 150 ohm resistor across the plus and minus leads on the TRS plug. Or 100 ohm or even 220 ohm. We know the thermal noise of that (it is in the -130 dbv range), and any additional noise above that will be the ADC. I'd check it at no gain and max gain (and maybe halfway in between). This will let you see what ADC noise is. You could do the same for the microphone inputs as well. This would let you determine EIN for those.

If you just test an open connection, you won't get values that tell you anything.

Also looking at your -60 db tests, it appears the dynamic range is about -112 db for the loopback. As the spec for the DAC and ADC is -115 db that is about as expected for both combined. This would make you think noise levels are modulated a bit by signal level at higher input levels.
 
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boXem

boXem

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Just a question. On the TRS inputs, you have selected Line In, and not Guitar/Instrument? They both use the same plug. You'd get higher noise on guitar/instrument because it is 1 megohm input impedance.
That's a good point.
Datasheet states that XLR input impedance is 2,65k, TRS is 1M.
Your hypothesis is making sense until we look at my measurements at 2V: noise is the same for TRS1->TRS1, TRS2->TRS2, TRS1->XLR1 (should not for this one), but is divided by two for TRS2->XLR2.
Doesn't make sense. Need to sleep on this.
 

lc155

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I didn't measure ADC noise by itself, so we don't know the noise source, could be the DAC.
When I am writing that I am disappointed, it's only because I will personally use it as an instrument for electronics testing. Not a judgement on intrinsic value as a sound card for musicians.

Now, as a normal user: looks cool, vu meter are cool too, even if quite slow, knobs are quite inaccurate.

Ah right, fair enough then. Yeah, I'm hoping to use it as a 3-in-1 as I described (mic, monitors, headphones). For the price point it seems almost too good to be true in that it can do all 3 things well, so I guess that is why I'm here seeing if that is indeed true or someone tears it apart, lol. I do have an o2dac but if I can simplify my setup without any discernable difference in quality I'll definitely jump at the chance.

Knobs being inaccurate is interesting but really not a big deal in the grand scheme so that's whatever for me.
 

Ykar

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Not really sure how to compare that but this is a loopback measurement from my Scarlett 2i2 Gen 2, TRS to TRS (right or left are same)


2020 05 01-DAC ADC Scarlett 2i2 loopback RCA droite %.jpg
 

Ykar

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Quite detailed video, thanks. By the way he's testing headphone output, so DAC + Amp while in the loopback measurements above it's DAC line out + ADC input. But still, given how Motu M2 performs, I can't believe loopback could measure worse than Scarlett 2i2 Gen 2. so I would bet on an issue in OP's measurement setup ?
 

lc155

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Looks like for those wanting a powerful headphone output into lower impedance phones the SSL 2 is the way to go according to the video above.

That's not what I gathered, he said the SSL2 sucks at <80ohm headphones due to high distortion.
 

Blumlein 88

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That's not what I gathered, he said the SSL2 sucks at <80ohm headphones due to high distortion.
Yeah that is why I removed the comment upon reflection.

BTW, when I've recorded and been in the room with the band, my solution was to use some very efficient in ear phones which could play on nearly no power. Put them in and cover my ears with passive or later noise canceling protective earphones. This got rid of the ambient sound almost completely and let you use the wimpy on-board phone outputs interfaces usually have. Some interfaces have very good sounding phone outs, but not many have powerful phone outs.
 
OP
boXem

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After installing latest REW beta + reinstalling JRE + cycling output gain knob max->min->max (yes, this was the trigger to get 10 dB lower noise!) I got much better noise figures. I also could measure multitone and jitter. And distortion figures in dB too :).
REW has become a fantastic tool.
I insert only channel 2 loopback, channel 1 has the same figures.
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I also measured SNR @ 115 dB as advertised.

Now I am happy of my purchase :cool:.
 
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