The Mudcat Café TM
Thread #155388   Message #3654850
Posted By: Mr Red
29-Aug-14 - 05:12 AM
Thread Name: Tech: Removing hum from old tapes
Subject: RE: Tech: Removing hum from old tapes
If it is on the tape you have a problem.
If it is in the digitising process there are things you can do.
1) check your earth loops.
2) run on batteries where possible (I do this for cassettes.)
3) I run the laptop on battery.
4) I have a Sweetex USB audio dongle which seems to isolate the audio better than on-board audio, but it is not entirely perfect. But any that brag of optical isolation will be best.
5) I put the laptop on a earthed metal plate (Tower side panel)

now the tape
If it was important enough I would investigate the possibility of subtracting the hum. (invert and add in Audacity, Cool Edit etc)
If you have enough footage that is without the desired audio, lead-in etc, then try to generate a waveform that is the same as the hum and subtract (invert & add). But it has to be said this is going to be an iterative process and need tweaking for level on each harmonic and phase for each harmonic (fundamental included). Being methodical would pay dividends. How important is it? How much patience have you got?
Thought not!