I use Line Level Shifters on all my equipment which also remove ground loop hum.
The best way to get control over hum is so make (solder) your own audio (cables and jacks). That way you have control on which jacks on the audio cable should have the ground wire cut plus you get the perfect length. I use multi cables with 16 or 24 cables inside so that you don't have hundreds och cables all over the room.
We are talking about jacks (1/4" or XLR) on audio cables. Do not remove ground on power cables or ground inside equipment!!
Jacks on the audio cable connected to an audio output of a device should have the ground wire connected (soldered).
Jacks on the audio cable connected to an audio input e.g. mixer should not have the ground wire soldered only the audio wires. Cut the ground wire and make sure you the complete ground wire. If you have some leads left and it touch theinside of the jack you can get hum. I usually pull and extend the plastic insulation cable, the outside cable a bit over the audio wires.
Hum can also occur in old equipment due to old capacitor in the power supply. Capacitor has a lifespan of about 30 years. If your 30 year old vintage synth, pre-amp start to hum, turn it off and replace the capacitors at ones.
You don’t want a capacitor blow up inside your expensive equipment… it is very messy and can ruin it.
How to avoid hum caused by ground loops: don't form ground loops. Use balanced signals wherever possible not just for noise immunity, but so you can "lift" the ground at any points that may cause trouble.