Audio, from zero Boring Solutions
Level 0 · Lesson 0.5

The uh-oh kit: no sound, hum, feedback, fixed fast

After this you can calmly triage the three most common live problems — no sound, hum, and feedback — by walking the chain in order instead of guessing.

First Sunday at the Board 9 min read

The hook

It's two minutes before the service. The worship leader steps up, the band's ready, and you bring up the first mic. Nothing. The lips are moving and the room is silent. Somewhere behind you a phone is already coming out to film the awkward part.

Here's the thing worth knowing before it happens: almost every live problem you'll hit is one of three, and none of them needs a panic. No sound, a hum or buzz that won't quit, or a squeal that takes over the room. Each one has a short, boring list of checks. You don't fix it by feel. You walk the chain in order, and the chain tells you where it broke.

This lesson is that list. Read it once now, tape a short version to the rack, and you'll never have to think your way out cold.

Video coming soon

The lesson

One idea sits under all three playbooks: the signal travels a path, and a problem lives at one spot on that path. You met the path in lesson 0.2 — mic, cable, channel, fader, out to the amp and speakers. When something's wrong, you don't poke at random. You walk the path from one end and find the broken link.

1. No sound

Work the chain from the mic to the speaker, in order. Stop the moment sound comes back — that's your culprit.

  1. Is the channel muted? Look for a lit MUTE button on the channel. This is the most common one. Unmute it.
  2. Is the fader up? A fader at the bottom sends nothing. Bring it to the 0 / unity mark.
  3. Is the gain up? If the fader's fine but the meter's dead, the gain (trim) was never set. Bring it up while they talk.
  4. Right input? Make sure the mic is plugged into the channel you're actually raising. Channel 4 won't move if the mic is in channel 5.
  5. Phantom power, for a condenser? A condenser mic needs +48V to work at all. No phantom, no sound. Switch it on for that channel and give it a second.
  6. Is the cable seated? Push the XLR in at both ends until it clicks. Half-seated cables are silent. A swap for a known-good cable rules it out.
  7. Is the amp or speaker on? If the whole room is dead, not just one channel, check that the amp or powered speakers are powered and turned up.

Nine times out of ten you stop at step one or two. The point of the order is that you never have to wonder what you've already ruled out.

2. Hum or buzz

A steady hum or buzz that's there whether or not anyone's talking is almost always a cable or a power problem, not a setting on the board. Run these quick checks:

  1. Swap the cable. Try a known-good cable on that channel first. A cracked cable or a failing connector is the single most common cause. This alone fixes most of them.
  2. Balanced, not the cheap stuff. A proper XLR or TRS cable is built to reject noise. A cheap unbalanced cable on a long run picks up hum like an antenna. Use the good cable.
  3. Laptop or DI on the same power? A laptop feeding the system — for lyrics, tracks, video — is a classic buzz source, especially on its charger. Run it through a DI box, or at least try it on the same power strip as the board.
  4. Anything electrical nearby? Light dimmers and lighting gear throw a nasty buzz into audio cables that run near them. Move the audio cable away from the lighting cable, or cross them instead of running them side by side.

If you've swapped to a good balanced cable and the hum's still there, you're likely looking at a ground issue between two pieces of gear. There's a real fix for that, and it gets its own treatment in a later level. For a Sunday, a good cable and a DI on the laptop clears most of it.

3. Feedback or squeal

Feedback is the rising squeal from lesson 0.4 — a mic hearing itself through the speakers and chasing the loop. When it starts, you don't diagnose. You kill it, then sort it out.

  1. Pull the offending fader. Find the channel that's ringing and bring its fader down. This breaks the loop instantly and quietly. If you're not sure which channel it is, pull the one you just raised, or pull the group/master a touch to calm the room while you find it.
  2. Bring the gain down a little. Once it's calm, the channel was probably running hotter than the room allows. Ease the gain back so it sits with more headroom under it.
  3. Move the mic or the source. Get the mic closer to the mouth (more voice for less level) and get it out of the line of the speakers. A mic pointed at a main speaker, or held out in front of a monitor, is feedback waiting to happen.

The instinct to fight a squeal by turning things up is exactly backwards. Down first, always. You can bring it back up carefully once the loop is broken.

Go deeperoptional

What hum actually is. The steady 60 Hz hum (50 Hz in much of the world) is the frequency of the AC power in the wall, leaking into your audio. It rides in two main ways. The first is a ground loop: when two pieces of gear are connected both through their audio cable and through their separate power grounds, that loop of wire acts like a single-turn transformer and a small 60-cycle current circulates in it, which you hear as hum. The second is induced noise: a power or lighting cable running alongside an audio cable couples its 50/60 Hz field (and its sharper harmonics — 120, 180 Hz, the buzzier edge) straight into the signal.

This is why balanced cables matter so much. A balanced line carries the audio twice, on two conductors with opposite polarity, plus a shield. Any hum induced along the run lands on both conductors equally. At the far end the gear takes the difference between the two and throws away anything they share — so the hum, being common to both, largely cancels. That trick is called common-mode rejection, and it's the whole reason pro audio runs balanced. An unbalanced cable has no second conductor to compare against, so whatever it picks up, you hear.

What feedback actually is. A feedback loop takes off when two conditions line up at once: the sound coming back to the mic is as loud as the sound that started it (the loop gain reaches 1), and it arrives back in phase, so each trip around stacks instead of cancelling. Miss either and it can't run away. That's why it locks onto one specific note — it's whichever frequency the room, the speakers, and the mic happen to keep both loud and in phase. Everything in playbook 3 is about dropping that loop gain back below 1: pulling the fader cuts it directly, backing off the gain lowers it, and moving the mic away from the speaker means less of the output gets back in to begin with.

Remember

  • Almost every live problem is one of three: no sound, hum, or feedback. Knowing that is half the calm.
  • Don't twiddle. Walk the chain in order, one check at a time. The chain tells you where it broke.
  • No sound: start at the mic, end at the speaker. Mute, fader, gain, input, phantom, cable, amp.
  • Hum is in the wiring (swap the cable first). Feedback is in the room (pull the fader first).
  • For feedback, down before up — always. You can bring it back once the loop is broken.

Your turn

  • Make your own uh-oh card: the three playbooks, short, on an index card. Tape it to the rack or the board.
  • Trace the no-sound chain on your actual board once, with the room empty, so the order is in your hands before you need it.
  • Cause a small, controlled bit of feedback during setup (mic toward a speaker, ease it up) so you know the sound and the fix before a Sunday.
  • Find which of your cables are balanced XLR/TRS and keep a known-good spare in the rack for the hum swap.