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Before I packed my Omnimic away again, I thought I'd take a quick comparison of distortion result between the Omnimic and my current setup consisting of a Line Audio OM1 and a Steinberg UR22mkii USB interface.
I always knew the Ominimic had a poor noise floor, so distortion measurements always had to be completed at a fairly high SPL just to get the harmonic products above the noise floor. It is just a basic integrated USB audio codec after all.
Comparing to the OM1, I completed sine sweeps at the same SPL, and adjusted the scaling and colours in ARTA so that the graphs can be directly compared. The SPL was fairly low, but just high enough to see something discernible above the noise floor in the Omnimic. At low frequency, the result is similar, but at high frequency there is a good 10dB+ advantage to the OM1.
As a double check of the noise floor, I simply ran the measurements with the output disconnected. There is probably even some further room for improvement on the OM1 with some gain adjustments to maximize SNR.
Dayton could really do with an update to the Omnimic, include a better USB codec like miniDSP did with their UMIK, and update the software to fix some of the bugs and reduce some of the annoyances. For example I shouldn't have to rerun a measurement to change the smoothing, and I should be able to select "play from soundcard" without hitting the play button first.