Motu M2 giving weirdly horrible performance

[bachatero]

I am testing my Motu M2's ADC just to see how good it is because I'm thinking of getting something better. When I played my 1kHz test tone through its DAC to the ADC, I get this chart:

What happened? The 1st harmonic is only -70dB below the fundamental which is horrible compared to what the ASR review showed. I double checked that my PC isn't doing anything funky (it probably isn't) so I have no clue what might be the culprit. Note: I'm using a balanced cable and the input gain is as low as it can be while leaving the tiniest of headroom to not clip.

 

[bachatero]

Any ideas?

 

[Blumlein 88]

You using ASIO?

 

[bachatero]

I'm using Linux so there's only Pipewire and ALSA.

 

[Philbo King]

Is the motu clock set to external?

 

[bachatero]

The Motu M2 doesn't support external clocks so it has to be the internal one

 

[Keith_W]

Are you 100% sure the ADC is not clipping? I suggest you re-run the test at different gain settings. Something is clipping there.

 

[bachatero]

Are you 100% sure the ADC is not clipping? I suggest you re-run the test at different gain settings. Something is clipping there.

I just tried it again and it's looking a lot better:

What's insane is that my special DAC EQ effects were turned on this time which is what's causing all that ugly noise to the left. However, the 1st harmonic is now a full -100dB, exactly what I expected. I didn't actually turn down the gain because it was already at minimum.

 

[AnalogSteph]

So what exactly has changed between the two measurements? Have you unplugged / replugged any cables or the like? Excessive H2/H4 can be an indication for poor contact of an opamp to its supplies in an unbalanced signal path, not sure whether there's any that qualify though. Likewise, I assume poor contact one of the input signal pins could do it. Were there any jacks involved that you had never used before?