Re: invert phase

First off, you are not affecting the signal in time, so the proper phrase is "polarity", not "phase".

It's a common misnomer - phase is time-dependent (you adjust the positive/negative placement of the sound wave in time); polarity is purely mechanical (positive voltage/negative voltage) and does not deal with time.

Secondly, ground loop noise finds its base frequency at 60Hz (in the US) and 50Hz (Europe, etc.). There can be harmonics (overtones), but they are not always a problem. You'll want to use a parametric filter to notch out the offending frequency. Start at 60Hz, with a narrow Q/Bandwidth, and boost the filter. Adjust the frequency until you find the loudest humming happening - that is the fundamental frequency, the rest are harmonics. Apply cut to the filter until it disappears or is out of the way enough to not be troublesome. IF IT AFFECTS THE AUDIO NEAGTIVELY, YOUR Q/BANDWIDTH IS SET TOO WIDE. Narrow it down and try again.

You can also use Spectrum View to ascertain what the fundamental frequency is and zone in on a solution that way.

Wolf
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