I had actually recently troubleshot the origin of the spurious 60 Hz mains noise to little more than the unshielded part of my in-ear mics, whereby even if completely driven off of my laptop, the tone would still show up on the RTA FFT, being expectedly highest near my desktop, diminishing further away within the house (though sometimes touching any part of my laptop or MOTU M2 may instead accentuate instead of attenuate the tone as though my body were behaving as an antenna), and being for the most part undetectable outside of the house though there are some power lines or other hanging around.
Otherwise, I would prefer for someone more technically experienced to chime on any theoretical merits of this device else properly debunk it.
For curiosity; 192 kHz sample rate used throughout:
Figure 1: A measurement I took with my in-ear mic from
https://audiosciencereview.com/foru...phone-measurements.18451/page-61#post-1956895 (post #1,210; I used the surviving right capsule in the left ear mount since the left capsule's wire snapped from wear) and a rough SPL calibration to acoustically confirm that my chain and Meze Elite were not introducing distortion sidebands hampering my ability to get past -36 dB on
https://www.klippel.de/listeningtes...+800Hz&outputDevice=Headphones&experience=Yes. Here, the irrelevant 60 Hz mains noise tone and its second harmonic are visible.
Figure 2: The result from letting the Klippel Listening Test introduce "-36 dB" distortion.
Figure 3: MOTU M2 outputting through a dual 6.35 mm TRS to 4.4 mm TRRRS adapter on the back input to my FiiO K9 Pro ESS's balanced line input, then outputting through a front 4-pin XLR to dual 3-pin XLR adapter and 6" 3-pin XLR extensions into a 1-to-3 3-pin XLR switchbox outputting to a dual 3-pin XLR to 4.4 mm TRRRS adapter hooked up to my 1.2 m Lavricables Grand (owned for bling and the opportunity to demonstrate acoustically immeasurable FR differences) that I use with my HE1000se, finally using what is technically a 3.5 mm to 6.35 mm TRS adapter to connect the left TS lead of the cable to the left mic input, its appearing to work just fine. Other than the initial input from the MOTU M2, this demonstrates the length of wire present in my usual listening.
Figure 4: Mic preamp gain set so that with that given volume knob setting, REW outputting a -12 dBFS 1 kHz tone is measured at a -12 dBFS level. As can be seen, there is no appreciable mains noise being picked up (though I don't know why 50 Hz is somewhat accentuated), just low-level spuriae and a 2 kHz harmonic possibly originating from the MOTU M2. I don't know where the 8 kHz and 16 kHz tones white are also present with no input are coming from. I don't know how the higher-impedance load of the mic preamp may be affecting the noise susceptibility compared to an actual 32 Ohm headphone load.
Figure 5: For additional curiosity, the result of playing a -6 dBFS (-5.1 dBFS was the minimum to not cause digital clipping, but -6 dBFS happened to be needed for the mic preamp to not clip) 1/10 decade multi-tone. I'd vie that these IMD spuriae originate from the MOTU M2 when loaded like this. Unless the behaviour has to do with the load, this may present an actual bottleneck for my multi-tone distortion measurements in
https://audiosciencereview.com/foru...phone-measurements.18451/page-61#post-1956895 (post #1,210).
Figure 6: Meze Elite mains noise measurement with my original unshielded in-ear mics.
Figure 7: Meze Elite mains noise measurement with my original unshielded in-ear mics while resting a hand on my MOTU M2.
Figure 8: Meze Elite mains noise measurement with my shielded in-ear mics and the same mic preamp gain. Again, per my multi-tone distortion measurement post, the problem was that these capsules had high second-order distortion at least when using the same VXLR+ adapter to power them. At least this is a decent proof of concept for the reduction of mains noise via appropriate microphone cable shielding.
Figure 9: The final result while resting a hand on the MOTU M2.