[Ardour-Users] Removing hum from track

[Al Thompson]

On 04/29/2017 12:28 PM, Ralf Mardorf wrote:
> On Fri, 28 Apr 2017 14:43:50 -0400, Al Thompson wrote:
>> Everyone is missing the simplest, least obtrusive method to eliminate
>> 60Hz hum on multitrack.  Just flip the phase of some of the tracks.  As
>> long as the tracks aren't related to each other (i.e.- stereo pairs)
>> there should be no adverse affect, and you won't have to kill low end
>> response.
> Hi,
>
> this unlikely works very good, if at all.
>
> Assuming the hum on different tracks would be completely in sync, so
> that inverting the phase would cancel out the hum, it still requires
> that the hum and inverted hum have the same energy. In reality
> the hum of several tracks neither is in sync, nor do they have the same
> energy and apart from this the hum could be some kind of modulated,
> resp. interacting with the wanted signal.
>
> The situation of recoded individual recorded and mixed tracks, is
> completely different to the situation of a balanced cable.
>
> Regards,
> Ralf

Well, if you tracked a rhythm section, then all of the drum tracks, and
whatever else you tracked at that time should certainly be synced.  As
for other tracks, it should be a fairly simple (but time-consuming)
matter to nudge a track a few 10ths of a millisecond so that the 60Hz
lines up.  Trying different combinations of tracks to phase reverse
should get a substantial reduction in hum.  And without the phase
anomalies created by trying to use narrow notch filters, and also
without ruining the low end.

I'd much rather use a screwdriver to adjust a problem, rather than a
sledgehammer to beat the daylights of out it.

This is the advantage of a DAW.  You CAN make fine adjustments, and try
limitless things to fix a problem (and undo them if they don't work)
instead of being forced to rely on such sonically destructive things as
steep slope narrow band filters.