A hum shows up mid-show. Ground lift? Cable swap? Switch over to battery? What's the panel's 30-second triage order when you're on the air?
ASKED BY · Paul Valhus · AUSTIN, TEXAS · 24 OCT 2026 · ▶ 00:24:02
Isolate the hum source; if from a specific input, use a notch filter at 60 Hz; if system-wide, test if unplugging the laptop power supply eliminates it, then use a ground lift adapter; laptop switching power supplies are common culprits.
Test and check equipment before shows to prevent surprises; use short quarter-inch cables into DI boxes to immediately balance unbalanced keyboard outputs.
Most hum comes from guitar cables or pedalboard connections; mute the first pedal board element to isolate; ensure proper sound checks beforehand; use DI boxes between laptops and soundboards; verify phantom power settings on microphones.
Summarised by AI from what the panel said. Watch the moment for the full answer.
From the transcript.
Machine-transcribed, so it may contain errors. Every timestamp opens the episode at that second.
23:38So that's a great place to be. All right. Let's move on. Courtney, what do we got next? From Paul Valhus in Austin, Texas. He says, a hum shows up mid-show. Ground lift? Cable swap? Switch over to battery? What's the panel's 30-second triage order when you're on the air? Oh, that's a tough one. Never something you want to have to deal with in the middle of a show.
24:05Courtney, what do you think? Obviously, this could be a lot of different things. Hum shows up mid-show. The singer has forgotten the lyrics, and you need to turn the teleprompter back on. No. You do have a problem at a live show because a hum, AC hum especially, 60 hertz hum or 120 hertz hum, usually is coming in over your AC power line.
24:27And you don't want to unplug your AC power line to anything that is carrying something like a live signal over the air to lift the power, lift the ground, unless you have ground lift, special ground lift switches in line already. So I would say the only way to deal with that is one, isolate this. See if you can isolate the source if it's coming in over an external audio source, like over one of the inputs to your mixer suddenly plugged something in and now it's coming in over a specific channel in your mixer.
24:59try and do a notch filter at 60 hertz on that particular input. If it's in general, in your PA in general, you've got a problem, you would have to take the power down to lift the ground. The other thing you can do is, if you're running off of a laptop, I find a lot of times laptop power supplies are the source of the hum. And if you've got a good battery in your laptop
25:22and you can unplug it to see if the hum goes away when you unplug the power supply to your laptop, And if it does, then try and lift the ground, put in a ground lifter, you know, one of those three to two adapters, AC adapters that we have in the United States. And if you're somewhere else, well, you're in Texas, that's kind of in the United States.
25:43Then you can put one of those in line and see if that solves the problem. A lot of times switching power supplies can generate noise and get leaky after a while. So a lot of times I've found that ground hum is coming from my laptop's power supply and I run off the batteries. And Ronny? I thought ground hum came from the ground, but it probably doesn't. So most of
26:08these situations that we experience is the bass guitarist has used his cable for something else that it should be used for, or the lead guitarist is using or leaving his cables with their kids using as a jump rope. So there are different ways, but eventually everything that we mostly experience is based on the stage floor right in front of the guitarist. They have these amazing
26:37pedal boards that do all this amazing stuff that only a scientific degree person is able to understand. And sometimes they have that linked to another pedal board with another set of pedals pedals that do all more amazing stuff. And all these pedal boards have a connection between them because there is a thing going through everything. And the easy check to check if that's the cable coming from the guitar or the guitar
27:03itself into the first pedal board is to just mute the first box on the pedal board and see if the hum is still there. If it's still there, well, then it's not the guitar cable. and then we have to of course find the faults in the pedalboard and a couple of weeks back we just asked the guitarist to change the cable and go directly into the amp and just jump over all the
27:30pedal boards and the hum were disappearing magically. So these are things that of course are really difficult to find out during the show. You should be able to have good sound checks before that and do really good line checks, not just seeing that there is a signal coming in, but actually listening to that and listening to what the signal is actually giving.
27:54If there is some hum, you address that immediately during the sound checks and try to prevent them from appearing in the show. And if you have a temporary thing that goes on during the sound check, you really should be aware because that can jump into and bite you during the show. And then of course you have what Courtney was talking about. Going from a laptop,